No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Characterization of the human quadriceps muscle in active elders
Abstract
To compare muscle activation deficits and muscle physiology in older versus younger adults.
A maximal volitional isometric contraction of the quadriceps muscle with burst-superimposition was used to assess strength and activation. In addition, force-frequency testing during fresh, fatigue, and recovery conditions and electrically elicited fatigue testing were performed.
Muscle performance laboratory.
Healthy, active young (age range, 20-28 yr) and older (age range, 66-83 yr) subjects.
Torque production, activation of the quadriceps, F50 values from the force-frequency relationships (frequency at which 50% of the maximum normalized force is produced), and the average amount of fatigue.
Older subjects were weaker (574.4 +/- 156 N) than younger subjects (900.9 +/- 295 N) and had significantly greater deficits in central activation in the quadriceps muscles (elderly = 95.5% activation; younger = 98.1% activation). The force-frequency curves for the elderly were to the left of the younger subjects for all 3 testing conditions. Aged muscles fatigued to the same extent as younger muscle (young = 49.8% +/- 2.6%, elderly = 51.1% +/- 2.8%).
These results can be used to modify high-intensity strength training protocols designed to optimize sustainable strength gains in the elderly during rehabilitation.
... However, in other studies that used a recovery time between contractions of 2-s, no difference was seen in fatigue profiles of young and older men. [13][14][15] It is unclear whether age-related differences in fatigue would be seen if the contraction and relaxation durations were both reduced to 2-s. It also remains to be determined whether sex differences similar to those seen in young individuals following intermittent fatiguing contractions 16 are also present in old, or whether such differences diminish, as was the case for sustained contractions of the arm flexors. ...
... 3 Quadriceps muscle fatigue following intermittent activation has been studied using voluntary 12,13 as well as electrically stimulated activation. [14][15][16] Electrical stimulation protocols have the advantage that they bypass possible bias related to central activation of muscle, such as the possibility that older people show greater decline in central activation 13,17 or a different response of the motor unit firing rate during fatiguing contractions. 11 They, therefore, provide a greater focus on factors at or distal to the neuromuscular junction and in the muscle itself as causes of fatigue. ...
... The torque-frequency relationship was determined using pre-set pulse width, voltage, and current (200 ms, 400 V, and the current, which differed between subjects, that elicited 25% MVC at 30 Hz). The muscle was stimulated at 7 different frequencies (1,10,15,20,30,50, and 100 Hz) in random order, separated by 60s, and with the tetani lasting 2-s. The maximal torque output at each frequency was recorded and expressed as a percentage of torque elicited at 100 Hz. ...
Introduction:
Susceptibility to muscle fatigue during aging could depend on muscle activation patterns.
Methods:
Young (mean age, 22 years) and older (mean age 70 years) men and women completed two fatigue tests of knee extensor muscles using voluntary and electrically stimulated contractions.
Results:
Older subjects displayed a shift to the left of the torque-frequency relationship and held a sustained voluntary isometric contraction at 50% maximal strength for significantly longer than young (P < 0.001). Young and old showed similar fatigue during electrically induced, intermittent isometric contractions (1-s on, 1-s off for 2 min), but women fatigued less than men (P = 0.001). Stronger muscles fatigued more quickly, and slower contractile properties were associated with longer sustained contractions.
Conclusions:
The slowing and weakness of older muscle was associated with superior fatigue resistance during sustained isometric contractions. Young and old showed similar fatigue following a series of brief, intermittent contractions, but women fatigued less than men.
... Impairments in voluntary muscle activation may contribute to the weakness commonly found in older adults. 4,6,18,21,26 Some studies have found age-related deficits in voluntary muscle activation, 4,6,9,19,22,26 but others have not. 3,10,16,17,24 This discrepancy may be explained by differences in the techniques used. ...
... 19 All the studies that found differences in voluntary muscle activation between young and older adults used a technique that delivered a high-frequency train of electrical pulses to the muscle during the contraction. 4,6,9,19,22,26 In contrast, all but one of the studies that found no such difference used a technique in which a single pulse was delivered to the contracting muscle. 3,10,16,17,24 When delivered at the same current amplitude, the high-frequency train of electrical pulses elicits a larger force response than the single pulse; thus, the high-frequency train may better resolve deficits in voluntary muscle activation. ...
... 2,20 Thus, at near maximum contraction intensities, only small changes in CARs were seen when there were large changes in relative force (%MVC). 18,20 In addition, because older adults have small but significant deficits in their CARs compared to young adults, 19,22 and because of the curvilinear relationship between the CAR and %MVC force, previous reports may have underestimated the actual differences in voluntary activation between young and old adults. An equation that describes the curvilinear relationship between the CAR and %MVC force has recently been developed for old and young adults. ...
The relationship between the central activation ratio (CAR) and contraction force is curvilinear, not linear as was previously believed. Voluntary quadriceps femoris muscle activation from previously collected data sets in 46 older adults (64-84 years) and 46 young adults (18-32 years) were therefore reexamined using a curvilinear model of the voluntary muscle activation-percent maximum voluntary force relationship. This method revealed lower voluntary muscle activation in older adults (0.868 +/- 0.018) than younger subjects (0.978 +/- 0.005). The mean difference between older and younger adults was 11%, which may be more meaningful than previous reports of 2-4% because it could explain the greater rate of strength loss as compared to loss of muscle mass as humans age.
... 7 Ten recent investigations have assessed the ability of young and older adults (Ն65 years of age) to activate their muscles during isometric maximum voluntary contractions (MVCs). 2,3,8,9,15,19,21,22,24,25 In half of the studies, no differences in voluntary muscle activation were found between young and older adults. 2,9,15,19,24 In the others, however, older adults were found to have lower measures of voluntary muscle activation than younger adults (e.g. ...
... 2,9,15,19,24 In the others, however, older adults were found to have lower measures of voluntary muscle activation than younger adults (e.g. 0.98 for young adults and 0.94 -0.95 for older adults 21,22 ). 3,8,21,22,25 One major methodological difference appears to explain this disparity: all the studies that found a difference used a high-frequency train of electrical pulses (or burst). ...
... 0.98 for young adults and 0.94 -0.95 for older adults 21,22 ). 3,8,21,22,25 One major methodological difference appears to explain this disparity: all the studies that found a difference used a high-frequency train of electrical pulses (or burst). In contrast, all but one of the studies that found no differences used a single electrical pulse delivered to the muscle when assessing voluntary muscle activation. ...
The purposes of this study were to develop and test a model describing the relationship between the central activation ratio (CAR; a measure of voluntary muscle activation) and percent maximum voluntary contraction (%MVC) force for old adults and to provide a method for more accurate determination of voluntary muscle activation failure. Twenty-one adults (ages 64-81) performed isometric testing of the quadriceps at 25%, 50%, 75%, and 100% MVC. During each contraction, a 100-HZ, 120-ms train of electrical pulses was delivered to the quadriceps muscle to quantify voluntary muscle activation. Similar to a young, healthy population (ages 20-35), a curvilinear relationship existed between the CAR and %MVC force for older adults. Predictions of subjects' MVCs using the linear model of CAR-%MVC force relationship generally demonstrated poor agreement with actual MVCs. Predictions of MVC from submaximal contractions (25%, 50%, and 75%) using a previously identified curvilinear young adult CAR-%MVC relationship were good [ICC (2,1): 0.81, 0.96, and 0.82, respectively]. Similar agreement was obtained from the curvilinear older adult CAR-%MVC relationship. These data suggest that the CAR-%MVC relationship is similar in young and older adult subjects and that curvilinear models of this relationship can predict MVC forces in older adults more accurately. Reexamination of the relationship between the CAR and %MVC force may allow a more accurate determination of how failure of voluntary muscle activation contributes to weakness in old adults.
... However, the impact of MU synchronization on VA has been recently brought into question [23]. Furthermore, given that the descending neural drive to the muscle precedes the onset of skeletal muscle contraction, it may be plausible that any preceding impairments along the descending neuroaxis impairs the subsequent activation of skeletal muscle and VA [24][25][26][27][28][29]. Hence, decreases in the descending neural drive could disallow activation of HT-MUs [30][31][32][33][34], thereby inducing losses of HT-MUs in older adults, increasing the risk of falls and decreasing physical performance [2,[27][28][29]. ...
... Furthermore, given that the descending neural drive to the muscle precedes the onset of skeletal muscle contraction, it may be plausible that any preceding impairments along the descending neuroaxis impairs the subsequent activation of skeletal muscle and VA [24][25][26][27][28][29]. Hence, decreases in the descending neural drive could disallow activation of HT-MUs [30][31][32][33][34], thereby inducing losses of HT-MUs in older adults, increasing the risk of falls and decreasing physical performance [2,[27][28][29]. The latter underlines the importance of preserving adequate functioning throughout all levels of the descending neuroaxis during the aging process to preserve physical performance and strength. ...
Age-related decline in voluntary force production represents one of the main contributors to the onset of physical disability in older adults and is argued to stem from adverse musculoskeletal alterations and changes along the descending neuroaxis. The neural contribution of the above is possibly indicated by disproportionate losses in voluntary activation (VA) compared to muscle mass. For young adults, resistance training (RT) induces muscular and neural adaptations over several levels of the central nervous system, contributing to increased physical performance. However, less is known about the relative neuroadaptive contribution of RT in older adults. The aim of this review was to outline the current state of the literature regarding where and to what extent neural adaptations occur along the descending neuroaxis in response to RT in older adults. We performed a literature search in PubMed, Google Scholar and Scopus. A total of 63 articles met the primary inclusion criteria and following quality analysis (PEDro) 23 articles were included. Overall, neuroadaptations in older adults seemingly favor top-down adaptations, where the preceding changes of neural drive from superior levels affect the neural output of lower levels, following RT. Moreover, older adults appear more predisposed to neural rather than morphological adaptations compared to young adults, a potentially important implication for the improved maintenance of neuromuscular function during aging.
... Joint components that undergo changes due to aging also contribute to the degeneration of hyaline cartilage. Osteoporosis or the weakening of the quadriceps muscle of the thigh leads to the dysfunction of the femorotibial joint, increasing the maximum stresses on the cartilage [36][37][38]. In the analysis of this study, a significant relationship was found between the presence of greater chondromolytic changes and increasing age for this group. ...
... It should be noted that obesity is not only associated with osteoarthritic changes of the knee joint in the mechanical but also in the metabolic background [39][40][41]. Through research, adipokines, leptin, and resistin, which have endocrine functions in adipose tissue, have been identified [38]. In vivo, findings have indicated that there is a detrimental effect on chondrocyte proliferation as well as the initiation of extracellular matrix metalloproteinase expression, resulting in reduced cartilage volume [42]. ...
Background and Objective: Magnetic resonance imaging (MRI) enables the effective evaluation of chondromalacia of the knee joint. Cartilage disease is affected by many factors, including gender, age, and body mass index (BMI). The aim of this study was to check the relationship between the severity of chondromalacia of the femoro-tibial joint and age, gender, and BMI assessed with 1.5T and 3.0T MRI scanners. Materials and Methods: The cross-observational study included 324 patients—159 (49%) females and 165 (51%) males aged 8–87 (45.1 ± 20.9). The BMI of study group was between 14.3 and 47.3 (27.7 ± 5.02). 1.5T and 3.0T MRI scanners were used in the study. The articular cartilage of the knee joint was assessed using the Outerbridge scale. Results: The age of the patients showed a significant correlation with Outerbrige for each compartment of the femorotibial joint (Spearman’s rank correlation rho: 0.69–0.74, p < 0.0001). A higher correlation between BMI and Outerbridge was noted in the femur medial (rho = 0.45, p < 0.001) and the tibia medial (rho = 0.43, p < 0.001) than in the femur lateral (rho = 0.29, p < 0.001) and the tibia lateral compartment (rho = 0.34, p < 0.001). Conclusions: The severity of chondromalacia significantly depends on age and BMI level, regardless of gender.
... Au contraire, chez les sujets fragiles, la perte de la fonction peut être atteinte plus précocement [Pendergast et al., 1993]. Neder et al. [1999] et Stevens et al. [2001] ont montré que la force du quadriceps, testée en isocinétique, est significativement réduite chez les sujets âgés comparativement aux sujets jeunes. De plus, ces derniers ont fait la preuve d'un recrutement central moindre chez les sujets âgés (95,5 % contre 98,1 %) [Stevens et al., 2001]. ...
... Neder et al. [1999] et Stevens et al. [2001] ont montré que la force du quadriceps, testée en isocinétique, est significativement réduite chez les sujets âgés comparativement aux sujets jeunes. De plus, ces derniers ont fait la preuve d'un recrutement central moindre chez les sujets âgés (95,5 % contre 98,1 %) [Stevens et al., 2001]. Les effets de la fatigue sont également plus importants pour les muscles des sujets âgés. ...
The ageing of cognitive, sensory, and motor systems, involved in postural control, induces a reduction of the functional capacities in the elderly, leading to an increased risk of falling. The consequences in terms of human and economic costs justify a growing interest in prevention. The general aim of this doctoral dissertation was to assess the efficiency of various physical therapies on the control of posture in elderly people. After evaluating various methods of clinical and instrumental investigation, we studied, on the one hand, the short- and medium-term effects of a program of sensorimotor, educational physical therapy of group, associating technical and cognitive handling. On the other hand, we selectively tested the short-term effects of various regional techniques usually practised by the physical therapists (massage and stretching) as well as self-training techniques. Overall, our results showed a positive effect on the clinical performances and control of short-term posture for the techniques taken separately, and in the medium- and long-term, for the program of physical therapy. The transfer to functional situations of everyday life and the reduction of the risk of falling remain to be studied.
... Au contraire, chez les sujets fragiles, la perte de la fonction peut être atteinte plus précocement [Pendergast et al., 1993]. Neder et al. [1999] et Stevens et al. [2001] ont montré que la force du quadriceps, testée en isocinétique, est significativement réduite chez les sujets âgés comparativement aux sujets jeunes. De plus, ces derniers ont fait la preuve d'un recrutement central moindre chez les sujets âgés (95,5 % contre 98,1 %) [Stevens et al., 2001]. ...
... Neder et al. [1999] et Stevens et al. [2001] ont montré que la force du quadriceps, testée en isocinétique, est significativement réduite chez les sujets âgés comparativement aux sujets jeunes. De plus, ces derniers ont fait la preuve d'un recrutement central moindre chez les sujets âgés (95,5 % contre 98,1 %) [Stevens et al., 2001]. Les effets de la fatigue sont également plus importants pour les muscles des sujets âgés. ...
Le vieillissement des systèmes sensoriels, effecteurs et cognitifs, participant au contrôle postural, induit une diminution des capacités fonctionnelles pouvant conduire à la chute chez la personne âgée. Les conséquences en terme de coût humain et économique justifient l’intérêt qui est porté aujourd’hui à leur prévention. L’objectif général de ce travail doctoral rentre dans cette problématique, en se focalisant plus particulièrement sur l’évaluation de l’efficacité de différentes prises en charge kinésithérapiques sur le contrôle de la posture des personnes âgées. Après s'être assuré de l'intérêt de diverses méthodes d'évaluation clinique et instrumentale, nous avons, d'une part, étudié l'effet à court et moyen terme d'un programme de kinésithérapie de groupe associant techniques sensorimotrices, éducatives et manipulations cognitives et, d’autre part, testé sélectivement les effets à court terme de différentes techniques régionales couramment pratiquées par les kinésithérapeutes (techniques de massage et étirements) et d’une technique d’autoentraînement. Dans leur ensemble, les résultats montrent un effet positif sur les performances cliniques et le contrôle de la posture à court terme pour les techniques prises isolément et à moyen et long terme, pour le programme de kinésithérapie. La traduction dans les situations fonctionnelles de vie quotidienne et la diminution du risque de chute restent à étudier.
... Stimulation patterns that reduce fatigue and optimize force output have been identified in several studies, but most tested young, able-bodied adults (Chou et al., 2008;Dreibati et al., 2010;Kaczmarek et al., 2010;Kesar and Binder-Macleod, 2006;Maladen et al., 2007). Only a limited number of studies have tested whether the motor response to stimulation found in young healthy adults are comparable to those seen in older adults Rice, 2001,2004;Klein et al., 1988;Narici et al., 1991;Stevens et al., 2001). Because disabling conditions such as stroke, Parkinson's Disease, and osteoarthritis primarily impact persons in middle to older ages (Hughes et al., 2010;Lloyd-Jones et al., 2009;Parkinson's Disease Foundation, 2010), it is critical that NMES rehabilitation regimens be customized to the unique motor behavior of older muscle. ...
... Less fatigue was observed in the thumb muscle of older compared to younger adults during a half-minute 30 Hz stimulation protocol (Narici et al., 1991). In contrast, no difference was seen in the fatigue response of older and younger individuals when the quadriceps was stimulated with a 40 Hz, 2.5-min protocol (Stevens et al., 2001) or when the triceps surae was stimulated with a 20 Hz protocol for 10 min (Klein et al., 1988). ...
a b s t r a c t Neuromuscular electrical stimulation (NMES) is typically used with older adults receiving rehabilitation therapies, but little is known about the stimulation patterns that maximize force output and minimize fatigue in this population. The purpose of this study was to apply variable patterns of stimulation to the thenar muscles of the hand in younger and older adults to determine if force production and neuro-muscular fatigue effects were similar. Three submaximal stimulation patterns were administered: A 20 Hz constant frequency pattern, a pattern that increased from 20 to 40 Hz, and a pattern that incorpo-rated two closely spaced (5 ms) doublet pulses. The doublet stimulation produced significantly higher average forces and force–time integrals (FTIs) than the constant frequency and increasing frequency pat-terns in both age groups. Additionally, older adults showed less fatigue than the younger group during isometric contractions performed after the fatiguing stimulation patterns. These results suggest that var-iable pulse NMES patterns enhance force production in the hand in both younger and older individuals better than constant frequency patterns, which are typically used in clinical applications. Also, greater fatigue resistance to electrical stimulation protocols may exist in the older population; this is critical information for the design and application of NMES rehabilitation regimens used with older adults.
... The activation level of the agonist quadriceps muscles significantly decreased with age (−12 %). This result was in agreement with part of the literature (Stackhouse et al. 2001;Stevens et al. 2001) and in disagreement with another part (Roos et al. 1999). In fact, it has been reported that voluntary activation in older adults could depend on the testing methods (De Serres and Enoka 1998) and/or the muscular group tested (De Serres and Enoka 1998;Kent-Braun and Ng 1999;Roos et al. 1999;Bilodeau et al. 2001;Stackhouse et al. 2001;Jakobi and Rice 2002;Morse et al. 2004). ...
... *p<0.05 and **p<0.01 significant difference between EMG coactivation level and mechanical ratio, respectively study showed that the decrease in activation level with age can be one of the parameters of the strength decrease in older men (Stackhouse et al. 2001;Stevens et al. 2001;Klass et al. 2007). Therefore, reduction in KE maximal agonist torque in older adults can be due to both contractile material alterations and neural impairments. ...
While it is often reported that muscular coactivation increases with age, the mechanical impact of antagonist muscles, i.e., the antagonist torque, remains to be assessed. The aim of this study was to determine if the mechanical impact of the antagonist muscles may contribute to the age-related decline in the resultant torque during maximal voluntary contraction in knee flexion (KF) and knee extension (KE). Eight young (19-28 years old) and eight older (62-81 years old) healthy males participated in neuromuscular testing. Maximal resultant torque was simultaneously recorded with the electromyographic activity of quadriceps and hamstring muscles. The torque recorded in the antagonist muscles was estimated using a biofeedback technique. Resultant torques significantly decreased with age in both KF (-41 %, p < 0.005) and KE (-35 %, p < 0.01). Agonist and antagonist torques were significantly reduced in KF (-44 %, p < 0.05; -57 %, p < 0.05) and in KE (-37 %, p < 0.01; -50 %, p < 0.05). The torque elicited by double twitch stimulation (-37 %, p < 0.01) and the activation level (-12 %, p < 0.05) of quadriceps was significantly lower in older men compared to young men. This study showed that antagonist torques were not responsible for age-related declines in KF and KE resultant torques. Therefore, decreased resultant torques with age, in particular in KE, can primarily be explained by impairments of the peripheral factors (excitation-contraction coupling) as well as by decreased neural agonist activation.
... Stimulation patterns that reduce fatigue and optimize force output have been identified in several studies, but most tested young, able-bodied adults (Chou et al., 2008;Dreibati et al., 2010;Kaczmarek et al., 2010;Kesar and Binder-Macleod, 2006;Maladen et al., 2007). Only a limited number of studies have tested whether the motor response to stimulation found in young healthy adults are comparable to those seen in older adults Rice, 2001,2004;Klein et al., 1988;Narici et al., 1991;Stevens et al., 2001). Because disabling conditions such as stroke, Parkinson's Disease, and osteoarthritis primarily impact persons in middle to older ages (Hughes et al., 2010;Lloyd-Jones et al., 2009;Parkinson's Disease Foundation, 2010), it is critical that NMES rehabilitation regimens be customized to the unique motor behavior of older muscle. ...
... Less fatigue was observed in the thumb muscle of older compared to younger adults during a half-minute 30 Hz stimulation protocol (Narici et al., 1991). In contrast, no difference was seen in the fatigue response of older and younger individuals when the quadriceps was stimulated with a 40 Hz, 2.5-min protocol (Stevens et al., 2001) or when the triceps surae was stimulated with a 20 Hz protocol for 10 min (Klein et al., 1988). ...
Neuromuscular electrical stimulation (NMES) is typically used with older adults receiving rehabilitation therapies, but little is known about the stimulation patterns that maximize force output and minimize fatigue in this population. The purpose of this study was to apply variable patterns of stimulation to the thenar muscles of the hand in younger and older adults to determine if force production and neuromuscular fatigue effects were similar. Three submaximal stimulation patterns were administered: A 20Hz constant frequency pattern, a pattern that increased from 20 to 40Hz, and a pattern that incorporated two closely spaced (5ms) doublet pulses. The doublet stimulation produced significantly higher average forces and force-time integrals (FTIs) than the constant frequency and increasing frequency patterns in both age groups. Additionally, older adults showed less fatigue than the younger group during isometric contractions performed after the fatiguing stimulation patterns. These results suggest that variable pulse NMES patterns enhance force production in the hand in both younger and older individuals better than constant frequency patterns, which are typically used in clinical applications. Also, greater fatigue resistance to electrical stimulation protocols may exist in the older population; this is critical information for the design and application of NMES rehabilitation regimens used with older adults.
... In the studies of first dorsal interosseus muscle, the discharge rate of motor units has been found to be more variable (33) and the maximal discharge rate to be smaller (29). Moreover, it is likely that the force-frequency curve of a muscle is modified with age (9,50,51,58). Additionally, monosynaptic reflexes in a hand muscle have been shown to be smaller, whereas longer latency responses are unchanged (12). ...
... force-frequency curve in combination with decreased discharge rate of motor units. It is not clear whether the force-frequency curve shifts to the left with age [adductor pollicis (50), quadriceps (58), tibialis anterior (9)] or not [tibialis anterior (51)]. But steeper slope in the force-frequency curve of the elderly has been reported for tibialis anterior muscle (9,51). ...
The objective of the study is to examine the effects of age and gender on finger coordination. Twelve young (24 +/- 8 yr; 6 men and 6 women) and 12 elderly (75 +/- 5 yr; 6 men and 6 women) subjects performed single-finger maximal contraction [maximal voluntary contraction (MVC)], four-finger MVC, and four-finger ramp force production tasks by pressing on individual force transducers. A drop in the force of individual fingers during four-finger MVC tasks compared with single-finger MVC tasks (force deficit) was larger, whereas unintended force production by other fingers during single-finger MVC tasks (enslaving) was smaller, in elderly than in young subjects and in women than in men. Force deficit was smaller and enslaving was larger in subjects with higher peak force. During the ramp task, the difference between the variance of total force and the sum of variances of individual forces showed a logarithmic relation to the level of total force, across all subject groups. These findings suggest that indexes of finger coordination scale with force-generating capabilities across gender and age groups.
... 41) In addition, the decline in muscle strength associated with aging may be owing to factors beyond muscle mass, such as de-creased proportion of fast type II fibers and reduced muscle excitatory neural activation. [42][43][44] Moreover, coactivation, which refers to opposing muscle mechanical action, is higher in older adults, resulting in reduced force production. 45) The assessment of grip strength using a HGS is a practical approach for evaluating muscle strength in clinical contexts. ...
Background:
The use of ultrasonographic echo intensity (EI) to evaluate skeletal muscle quality and its effects on strength, explosive power, and physical function (PF) in older individuals remains unclear. This meta-analysis evaluated the associations among EI, muscle strength (MS), and PF in older individuals.
Methods:
We conducted a systematic search of the PubMed, Embase, Web of Science, SPORT Discus, and CINAHL databases through October 2022 to identify primary studies examining the association between EI and MS/PF. Effect sizes were computed using a random-effects model and presented using forest plots. Pearson's r-values and I2 statistics were used to measure heterogeneity.
Results:
This meta-analysis included 24 patients. EI demonstrated a negative association with maximal strength (r = -0.351, 95% confidence interval [CI]: -0.411 to -0.288, P < 0.001) and explosive power (r = -0.342, 95% CI: -0.517 to -0.139, P = 0.001) in older individuals. Handgrip strength also showed a significant negative correlation with EI (r = -0.361, 95% CI: -0.463 to -0.249, P < 0.001). However, we observed only a small and non-significant negative association between EI and gait speed (r = -0.003, 95% CI: -0.083 to -0.077, P = 0.943), and a weak non-significant correlation with the chair stand test (r = 0.072, 95% CI: -0.045 to 0.187, P = 0.227).
Conclusion:
Increased EI was associated with lower strength and power but not with gait speed or chair test performance in older individuals. Further large-sample studies with long-term follow-up are needed to improve frailty prediction and risk assessment in this population.
... Many age-dependent factors such as gradual strength loss of quadriceps muscle and increased oxidative stress in the knee joint microenvironment contribute to this process [30][31][32][33][34]. ...
Background and Objectives: Osteoarthritis (OA) of the knee is a degenerative disorder characterized by damage to the joint cartilage, pain, swelling, and walking disability. The purpose of this study was to assess whether demographic and radiologic parameters (knee diameters and knee cross-sectional area from magnetic resonance (MR) images) could be used as surrogate biomarkers for the prediction of OA. Materials and Methods: The knee diameters and cross-sectional areas of 481 patients were measured on knee MR images, and the corresponding demographic parameters were extracted from the patients’ clinical records. The images were graded based on the modified Outerbridge arthroscopic classification that was used as ground truth. Receiver-operating characteristic (ROC) analysis was performed on the collected data. Results: ROC analysis established that age was the most accurate predictor of severe knee cartilage degeneration (corresponding to Outerbridge grades 3 and 4) with an area under the curve (AUC) of the specificity–sensitivity plot of 0.865 ± 0.02. An age over 41 years was associated with a sensitivity and specificity for severe degeneration of 82.8% (CI: 77.5–87.3%), and 76.4% (CI: 70.4–81.6%), respectively. The second-best degeneration predictor was the normalized knee cross-sectional area, with an AUC of 0.767 ± 0.04), followed by BMI (AUC = 0.739 ± 0.02), and normalized knee maximal diameter (AUC = 0.724 ± 0.05), meaning that knee degeneration increases with increasing knee diameter. Conclusions: Age is the best predictor of knee damage progression in OA and can be used as surrogate marker for knee degeneration. Knee diameters and cross-sectional area also correlate with the extent of cartilage lesions. Though less-accurate predictors of damage progression than age, they have predictive value and are therefore easily available surrogate markers of OA that can be used also by general practitioners and orthopedic surgeons.
... Quadriceps ekstansiyon kas kuvveti, dinamometreye bağlı ayak bileğinden uygulanan kuvvet ile ölçülür (52) . Yaş, boy ve cinsiyete göre referans değerleri vardır (53) . ...
... This is supported by the reduced leg stiffness values with raising box height (i.e., task demand) even in younger adults. However, based on the current findings we cannot exclude that the middle-aged adults were not able to stiffen their lower limb joints to the same amount as younger adults, due to deficits in leg extensor muscle activation, for example (Stackhouse et al., 2001;Stevens et al., 2001;Morse et al., 2004;Clark et al., 2013). ...
Reductions in muscular power output and performance during multi-joint motor tasks with aging have often been associated with muscle weakness. This study aimed to examine if matching younger and middle-aged adults for triceps surae (TS) muscle strength and tendon stiffness eliminates age-related differences in muscular power production during drop jump. The maximal ankle plantar flexion moment and gastrocnemius medialis tendon stiffness of 29 middle-aged (40–67 years) and 26 younger (18–30 years) healthy physically active male adults were assessed during isometric voluntary ankle plantar flexion contractions using simultaneous dynamometry and ultrasonography. The elongation of the tendon during the loading phase was assessed by digitizing the myotendinous junction of the gastrocnemius medialis muscle. Eight younger (23 ± 3 years) and eight middle-aged (54 ± 7 years) adults from the larger subject pool were matched for TS muscle strength and tendon stiffness (plantar flexion moment young: 3.1 ± 0.4 Nm/kg; middle-aged: 3.2 ± 0.5 Nm/kg; tendon stiffness: 553 ± 97 vs. 572 ± 100 N/mm) and then performed series of drop jumps from different box heights (13, 23, 33, and 39 cm) onto a force plate (sampling frequency 1000 Hz). The matched young and middle-aged adults showed similar drop jump heights for all conditions (from lowest to highest box height: 18.0 ± 3.7 vs. 19.7 ± 4.8 cm; 22.6 ± 4.2 vs. 22.9 ± 4.9 cm; 24.8 ± 3.8 vs. 23.5 ± 4.9 cm; 25.2 ± 6.2 vs. 22.7 ± 5.0 cm). However, middle-aged adults showed longer ground contact times (on average 36%), lower vertical ground reaction forces (36%) and hence lower average mechanical power (from lowest to highest box height: 2266 ± 563 vs. 1498 ± 545 W; 3563 ± 774 vs. 2222 ± 320 W; 4360 ± 658 vs. 2475 ± 528 W; 5008 ± 919 vs. 3034 ± 435 W) independent of box height. Further, leg stiffness was lower (48%) in middle-aged compared to younger adults for all jumping conditions and we found significant correlations between average mechanical power and leg stiffness (0.70 ≤ r ≤ 0.83; p < 0.01). Thus, while jumping performance appears to be unaffected when leg extensor muscle strength and tendon stiffness are maintained, the reduced muscular power output during lower limb multi-joint tasks seen with aging may be due to age-related changes in motor task execution strategy rather than due to muscle weakness.
... Particularly, for normal function of the knee joints, balance of the vastus medialis and vastus lateralis muscles is very important (Stevens, et al., 2010). Most previous studies have looked at contribution degree of muscles that passed the quadriceps muscle and knee joints for the strengthening of the lower limb muscles and examined knee extension, weight bearing terminal knee extension, step exercise, and semi-squat as desirable exercise methods for the balance of the quadriceps muscle (Libingston, 1998). ...
PURPOSE: This study intends to examine the effects of change of anatomical position of the ankle joint in open kinematic chain, an appropriate position for selective muscle training, on vastus lateralis obliques, rectus femoris, vastus medilais obliques, and rectus abdominalis muscle activation and to present an effective method of muscle training for patients and normal people. METHODS: The participants of this study were Korean healthy adult in their 20s. The 8 channel surface electromyography was used to measure muscle activation while the subjects raised their legs under each condition. Under each condition, while the subjects raised the leg to hip joint flexion at 60^{\circ} along the arch. RESULTS: The analysis result of muscle activation by each section and position during leg rising. There were significant differences. CONCLUSION: For independent strengthening of each muscle, muscle activation was measured according to leg raising angles and the result differed according to each section and position. If this study result is applied to muscle training for patients who need selective muscle training, more effective muscle strengthening will be made possible.
... 57 Reference values are available. 58 ...
In patients with chronic obstructive pulmonary disease (COPD), skeletal muscle dysfunction is a major comorbidity that negatively impacts their exercise capacity and quality of life. In the current guidelines, the most recent literature on the various aspects of COPD muscle dysfunction has been included. The Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) scale has been used to make evidence-based recommendations on the different features. Compared to a control population, one third of COPD patients exhibited a 25% decline in quadriceps muscle strength, even at early stages of their disease. Although both respiratory and limb muscles are altered, the latter are usually more severely affected. Numerous factors and biological mechanisms are involved in the etiology of COPD muscle dysfunction. Several tests are proposed in order to diagnose and evaluate the degree of muscle dysfunction of both respiratory and limb muscles (peripheral), as well as to identify the patients' exercise capacity (six-minute walking test and cycloergometry). Currently available therapeutic strategies including the different training modalities and pharmacological and nutritional support are also described.
Copyright © 2014 SEPAR. Published by Elsevier Espana. All rights reserved.
... This is a protective mechanism prevent future reinjury. Stevens et al. found the incidence of activation failure in young healthy subjects is approximately 10% [77]. In ACL-deficient subjects the incidence of complete inactivation is approximately 30% and can be bilateral [78]. ...
The rehabilitation of patients undergoing anterior cruciate ligament (ACL) reconstruction requires symmetry in bilateral quadriceps strength and adequate proprioception capabilities prior to return to preoperative level of activity or sport. This is the limiting factor and can delay the time that patients can return to play. There is little literature on pre-operative physiotherapy or prehabilitation of patient with ACL injury. This paper discusses the anatomy, biomechanics, surgical decision making, and the current knowledge of preoperative training or “prehabilitation” in patients awaiting ACL reconstruction.
... Subchondral bone softening, which occurs during age-related osteoporosis [78], is predicted to alter the biomechanics of the tibiofemoral joint by increasing the maximum tensile strains in cartilage and the magnitudes of joint contact pressure [79]. In addition, due to the aged less activity, the declined quadriceps strength may be another factor responsible for altered joint loading patterns as a consequence of joint laxity [80]. Nonphysiological load or less mechanical load exerted on chondrocytes would induce catabolic signaling and cartilage tissue breakdown [59]. ...
Osteoarthritis (OA) is closely associated with aging, but its underlying mechanism is unclear. Recent publications were reviewed to elucidate the connection between aging and OA. With increasing OA incidence, more senior people are facing heavy financial and social burdens. Age-related OA pathogenesis is not well understood. Recently, it has been realized that age-related changes in other tissues besides articular cartilage may also contribute to OA development. Many factors including senescence-related secretory phenotypes, chondrocytes' low reactivity to growth factors, mitochondrial dysfunction and oxidative stress, and abnormal accumulation of advanced glycation end products (AGEs) may all play key roles in the pathogenesis of age-related OA. Lately, epigenetic regulation of gene expression was recognized for its impact on age-related OA pathogenesis. Up to now, few studies have been reported about the role of miRNA and long-noncoding RNA (lncRNA) in age-related OA. Research focusing on this area may provide valuable insights into OA pathogenesis. OA-induced financial and social burdens have become an increasingly severe threat to older population. Age-related changes in noncartilage tissue should be incorporated in the understanding of OA development. Growing attention on oxidative stress and epigenetics will provide more important clues for the better understanding of the age-related OA.
... It has been observed that a decline in isometric voluntary strength with ageing may be accompanied by a decrease in the capacity for the neural activation of the muscles (Doherty, Vandervoort, & Brown, 1993;Stevens, Binder-Macleod, & Snyder-Mackler, 2001). However, the present study indicated no signifi cant differences in twitch PT/voluntary strength ratio in physically active women with increasing age. ...
Twitch contractile properties of the plantar flexor muscles were compared between the groups of women of the 3 rd , 5 th , 6 th and 8 th decade participating in regular recreational physical activity. An isometric twitch was evoked by supramaximal electrical stimulation of the tibial nerve in the popliteal fossa by a rectangular pulse of 1 millisecond duration. A significant decrease was found in the twitch peak force, the maximal rates of force development and relaxation from the 6 th decade onwards. A significant prolongation in twitch contraction time was observed from the 5 th decade onwards. The 3 rd decade group showed a significant post-activation potentiation, while the three older groups did not. No significant age-related changes were observed in the isometric twitch peak force and voluntary strength ratio, and the twitch half-relaxation time in women participating in regular recreational physical activity. It was concluded that the marked decrease in twitch force-potentiation and prolongation of the contraction time of the plantar flexor muscles in physically active women seem to begin after 40 years of age, while a reduction in the maximal voluntary and twitch force-generating capacity, and twitch contraction kinetics occurs after 50 years of age.
... However, in our study, although statistically significant, the influence of muscle quality assessed from EI on muscle strength was relatively low, accounting for 16% of the variance. These data suggest that age-related decreases in muscle strength may be associated with factors other than muscle quality, including a reduced proportion of fast type II fibers (Larsson 1997;Sipilä et al. 2004) and decreased neural activation of the agonist muscle (Stevens et al. 2001). In addition, coactivation (the opposing mechanical action of the antagonist muscle) is reported to be higher in elderly adults and may contribute to reduced force production (Izquierdo et al. 1999;Macaluso et al. 2002). ...
Enhanced echo intensity (EI) on an ultrasound image of skeletal muscle indicates changes in muscle quality, including increases in intramuscular fibrous and adipose tissues. However, it is not known whether muscle quality assessed from the EI of computer-aided gray-scale analysis of an ultrasound image is associated with the muscle strength or body composition of a subject. The objectives of this study were to investigate whether muscle quality assessed from EI measured using gray-scale analysis is associated with muscle strength independently of age or muscle thickness (MT), and to examine the relationship between muscle EI and body composition. Ninety-two healthy women with a mean age of 70.4 ± 5.5 years (range, 51-87 years) dwelling in Kyoto, Japan, participated in the study. The MT, subcutaneous fat thickness (FT), and EI of the quadriceps femoris on the right extremity were assessed from transverse ultrasound images. Knee extensor isometric strength was used as a measure of the quadriceps femoris muscle strength. EI was significantly correlated with quadriceps strength independently of age or MT, and stepwise regression analysis revealed that MT and EI were independently associated with quadriceps strength. Importantly, EI showed no significant correlations with FT, percentage of body fat (%BF), or body mass index (BMI), while FT, BMI, and %BF did not significantly influence muscle strength. These data suggest that muscle quantity (i.e., MT) and muscle quality assessed from EI measured using computer-aided gray-scale analysis independently contribute to muscle strength in middle-aged and elderly persons.
... Studies reporting on the quadriceps have stated that 90% to 100% represents the range of normal voluntary activation values among the general population. 17,18 Conversely, values below 90% are considered clinically meaningful deficits. In this study the nonfatigued voluntary activation of the infraspinatus was 96%, and voluntary activation dropped to 89% in the fatigued state. ...
Neuromuscular inhibition of the infraspinatus would be greater and external rotation muscle force would be lower after a simulated game compared with pregame values.
The sample included 21 uninjured, asymptomatic high school-aged baseball pitchers. Maximum volitional shoulder external rotation strength was assessed before and after a simulated game with a clinical dynamometer. Voluntary activation of the infraspinatus was assessed during strength testing by a modified burst superimposition technique. Performance-related fatigue was assessed by monitoring pitch velocity, and global fatigue was assessed by subject self-report before and after the game. Statistical testing included paired and independent t tests, with α ≤ .05.
There was no difference between throwing and non-throwing shoulder external rotation strength (P = .12) or voluntary infraspinatus activation (P = .27) before the game. After the game, voluntary activation was significantly lower in the throwing limb compared with pregame activation levels (P = .01). Lower external rotation strength after the game approached statistical significance (P = .06). Pitch velocity was lower in the final inning compared with first-inning velocity (P = .01), and fatigue was significantly greater after the game (P = .01).
Voluntary infraspinatus muscle activation is a mechanism contributing to external rotation muscle weakness in the fatigued pitcher. Understanding mechanisms contributing to muscle weakness is necessary to develop effective injury prevention and rehabilitation programs. Treatment techniques that enhance neuromuscular activation may be a useful strategy for enhancing strength in this population.
... Maximal voluntary isometric contraction (MVIC) of the quadriceps muscle was measured on a Kin Com dynamometer (KinCom, Chattanooga, Hixon, TN). 5,7,19 Participants were seated with their hips flexed to 85° and their knees flexed to 75°. Prior to testing, participants practiced using submaximal contractions at 50% and 75% of their maximal effort to familiarize themselves with the testing procedure. ...
Many older individuals have persistent quadriceps strength impairments after a total knee arthroplasty (TKA). A combination of muscle atrophy and neuromuscular activation deficits apparently contributes to residual strength impairments. The purpose of this short report is to describe the contribution of quadriceps muscle activation and muscle volume to impaired muscle strength in older individuals an average of 21 months following a TKA.
Seventeen individuals (males: 3, females: 14; mean age: 68 yrs +/- 8.7; BMI: 33 +/- 4.8 kg/m2; number of TKA: 24; average postoperative months: 21 +/- 11.3) recruited from an orthopaedic surgeon's practice provided their written consent and participated in this study. Quadriceps strength (MVIC) and voluntary quadriceps muscle activation (QA) were measured with use of a burst-superimposition technique in which a supramaximal burst of electrical stimulation is superimposed on an MVIC. Quadriceps volume (QV) was assessed from magnetic resonance images of the quadriceps.
The mean quadriceps strength was 107.3 Nm +/- 36.4 (range: 43.22 - 205.2). The mean QA (as described with a central activation ratio) was 0.97 +/- 0.04 (range: 0.83 - 1.00). The mean QV was 1093 cm3 +/- 311.80 (range: 653.66 - 1706.56). QA and QV explain 85% of the variance in quadriceps strength (R2 = .85, p < 0.001), with QV having the greatest contribution to strength (R2 = .77, p < 0.001).
QV is a much stronger predictor of quadriceps strength than QA in individuals more than 1 year following TKA. Activation levels contributed little to strength one year following TKA, compared to its profound contribution in the first few postoperative months. Physical therapy interventions focused on improving muscle size in this population should be considered more relevant than countermeasures addressing neuromuscular activation.
... Both groups demonstrated slightly reduced values for muscle strength, 24 both for the MVC-Q, which was 32. Table 1. ...
Previous studies have used electrical neuromuscular stimulation as a physical training method in patients with severe COPD. We introduce the use of the more tolerable magnetic stimulation for the same purpose, investigating the effectiveness of an eight-week protocol.
Eighteen patients with severe COPD were randomly assigned to a magnetic stimulation training protocol, n=10, FEV(1)=30% (SD: 7) or to parallel clinical monitoring, control group, n=8, FEV(1)=35% (SD: 8). During eight weeks, patients were stimulated for 15min on each quadriceps femoris, three times per week. Quadriceps muscle strength and endurance measurements, quality-of-life questionnaires (SF36, SGRQ) and a six-minute walking test were all carried out before and after the training period in the stimulated and control subjects.
All patients completed the training with increasing intensity of stimulation, displaying a significant improvement in voluntary quadriceps strength (17.5% of the baseline value) and exercise capacity, with a mean increase of 23m in the six-minute walking test. The questionnaire scores showed greater increases in quality-of-life scores in the trained subjects compared to the controls, particularly in the physical function areas: mean increments in SF36 in "physical function": +26, "role limitations due to physical problems": +40 and "vitality": +17.5, while +13, -4 and +1, respectively in controls. Saint George's "Activity" score improved by 19.6 points, for 11.5 in controls.
In COPD patients who are limited due to dyspnoea, magnetic neuromuscular stimulation of the quadriceps constitutes a feasible training method for the lower limbs, with positive effects on the muscle function, effort capacity and perception areas.
... Quadriceps strength and activation testing. Quadriceps strength and volitional muscle activation were measured using a burst superimposition technique (22), which is a validated quadriceps strength assessment widely used in a variety of populations with and without knee pathologies (6,(23)(24)(25)(26). Briefly, subjects' knees were stabilized in 75°of flexion on a dynamometer (KinCom). ...
To determine the effectiveness of progressive quadriceps strengthening with or without neuromuscular electrical stimulation (NMES) on quadriceps strength, activation, and functional recovery after total knee arthroplasty (TKA), and to compare progressive strengthening with conventional rehabilitation.
A randomized controlled trial was conducted between July 2000 and November 2005 in an academic outpatient physical therapy clinic. Two hundred patients who had undergone primary, unilateral TKA for knee osteoarthritis were randomized to 1 of 2 interventions 4 weeks after surgery, and 41 patients eligible for enrollment who did not participate in the intervention were tested 12 months after surgery (standard of care group). All randomized patients received 6 weeks of outpatient physical therapy 2 or 3 times per week through 1 of 2 intervention protocols: an exercise group (volitional strength training) or an exercise-NMES group (volitional strength training and NMES). Treatment effects were evaluated by a burst superimposition test to assess quadriceps strength and volitional activation 3 and 12 months postoperatively. The Medical Outcomes Study Short Form 36 and Knee Outcome Survey were completed. Knee range of motion, Timed Up and Go, Stair-Climbing Test, and 6-Minute Walk were also measured.
Strength, activation, and function were similar between the exercise and exercise-NMES groups at 3 and 12 months. The standard of care group was weaker and exhibited worse function at 12 months compared with both treatment groups.
Progressive quadriceps strengthening with or without NMES enhances clinical improvement after TKA, achieving similar short- and long-term functional recovery and approaching the functional level of healthy older adults. Conventional rehabilitation does not yield similar outcomes.
... Quadriceps activation was estimated by utilising the burstsuperimposition technique on a maximum voluntary isometric contraction (MVIC). The burst-superimposition technique provides the muscle with a percutaneous supramaximal stimulus to recruit any remaining muscle fibres which have not been stimulated (Rutherford et al., 1986;Snyder-Mackler et al., 1994;Stevens et al., 2001). A superimposed burst (100 pulses/s, 600 ms pulse duration, 10 pulse tetanic train, 125 V, 100 ms duration) was manually applied to the quadriceps approximately 2 s after the beginning of the MVIC when the experimenter determined a plateau in force had occurred. ...
Lumbopelvic joint manipulation has been shown to increase quadriceps force output and activation, but the duration of effect is unknown. It is also unknown whether lower grade joint mobilisations may have a similar effect. Forty-two healthy volunteers (x+/-SD; age=28.3+/-7.3 yr; ht=172.8+/-9.8 cm; mass=76.6+/-21.7 kg) were randomly assigned to one of three groups (lumbopelvic joint manipulation, 1 min lumbar passive range of motion (PROM), or prone extension on elbows for 3 min). Quadriceps force and activation were measured using the burst-superimposition technique during a seated isometric knee extension task before and at 0, 20, 40, and 60 min following intervention. Collectively, all groups demonstrated a significant decrease (p<0.001) in quadriceps force output without changes in activation (p>0.05) at all time intervals following intervention. The group that received a lumbopelvic joint manipulation demonstrated a significant increase in quadriceps force (3%) and activation (5%) (p<0.05) immediately following intervention, but this effect was not present after the 20 min interval. Since participants in this study were free of knee joint pathology, it is possible that they did not have the capacity to allow for large changes in quadriceps muscle activation to occur.
This historical review summarizes the major advances - particularly from the last 50 years - in transcutaneous motor-level electrical stimulation, which can be used either as a tool to investigate neuromuscular function and its determinants (electrical stimulation for testing; EST) or as a therapeutic/training modality to improve neuromuscular and physical function (neuromuscular electrical stimulation; NMES). We focus on some of the most important applications of electrical stimulation in research and clinical settings, such as the investigation of acute changes, chronic adaptations and pathological alterations of neuromuscular function with EST, as well as the enhancement, preservation and restoration of muscle strength and mass with NMES treatment programs in various populations. For both EST and NMES, several major advances converge around understanding and optimizing motor unit recruitment during electrically-evoked contractions, also taking into account the influence of stimulation site (e.g., muscle belly vs nerve trunk) and type (e.g., pulse duration, frequency, and intensity). This information is equally important both in the context of mechanistic research of neuromuscular function as well as for clinicians who believe that improvements in neuromuscular function are required to provide health-related benefits to their patients.
Total knee arthroplasty (TKA) is a common treatment for osteoarthritis of the knee joint. A decrease in lower extremity power is commonly seen in older adults who have knee osteoarthritis and TKA. This review integrates the current evidence regarding the change in lower extremity muscle power following TKA, rehabilitation efforts to improve power following TKA, and changes in muscle power related to function after TKA. It is recommended that lower extremity muscle power be measured and rehabilitated appropriately following TKA. A need for future research examining best treatment protocols to develop lower extremity power after TKA is warranted.
One of the most widely conserved hallmarks of aging is a decline in functional capabilities. Mobility loss is particularly burdensome due to its association with negative health outcomes, loss of independence and disability, and the heavy impact on quality of life. Recently, a new condition, physical frailty and sarcopenia, has been proposed to define a critical stage in the disabling cascade. Physical frailty and sarcopenia are characterized by weakness, slowness, and reduced muscle mass, yet with preserved ability to move independently. One of the strategies that have shown some benefits in combatting mobility loss and its consequences for older adults is physical activity. Here, we describe the opportunities and challenges for the development of physical activity interventions in people with physical frailty and sarcopenia. The aim of this article is to review age-related physio(patho)logical changes that impact mobility in old age and to provide recommendations and procedures in accordance with the available literature.
Whether there are age-related differences in neural drive during maximal effort contractions is not clear. This review determined the effect of age on voluntary activation during maximal voluntary isometric contractions (MVC). The literature was systematically reviewed for studies reporting voluntary activation quantified with the interpolated twitch technique (ITT) or central activation ratio (CAR) during isometric contractions in young (18-35 years) and old adults (>60 years, mean ≥65 years). Of the 2,697 articles identified, 54 were eligible for inclusion in the meta-analysis. Voluntary activation was assessed with electrical stimulation (ES) and transcranial magnetic stimulation (TMS) on 5 different muscle groups. Random-effects meta-analysis revealed lower activation in old compared with young adults (d=-0.45, 95% CI [-0.62 - -0.29], p<0.001), with moderate heterogeneity (52.4%). To uncover the sources of heterogeneity, subgroup analyses were conducted for muscle group, calculation method (ITT or CAR), and stimulation type (ES or TMS) and number (single, paired or train stimulations). The age-related reduction in voluntary activation occurred for all muscle groups investigated except the ankle dorsiflexors. Both ITT and CAR demonstrated an age-related reduction in voluntary activation of the elbow flexors, knee extensors and plantar flexors. ITT performed with paired and train stimulations showed lower activation for old than young adults with no age difference for the single electrical stimulation. Together, the meta-analysis revealed that healthy older adults have a reduced capacity to activate some upper and lower limb muscles during MVCs; however, the effect was modest and best assessed with at least paired stimulations to detect the difference.
A forward trunk lean sometimes occurs to compensate for quadriceps muscle weakness. Since muscle weakness in the lower extremities is commonly observed in the elderly, quadriceps weakness may trigger age-related postural change. The objective of this study was to ascertain the association between forward trunk lean during walking and musculoskeletal strength in females aged between 46 and 79 years. Musculoskeletal functions (range of joint motion, degree of kyphosis, muscle strength) and joint moments during walking were measured for 13 females. Subjects who showed greater joint moments during walking tended to lean more. Moderate association was seen between mean trunk angle during walking and knee extension moment (r = 0.535, p = 0.060). There was no statistically significant correlation between the strength of the quadriceps muscle and the mean trunk angle in walking subjects (r = 0.095, p = 0.758). These observations suggested that muscle weakness in the quadriceps is largely independent of leaning of the trunk for this sample of subjects. Other factors may change the posture to a stoop, such as severe thoracic kyphosis, poor balance control, or fear of falling.
Knee replacement surgery has undergone a rapid and significant growth over the past three decades strongly supported by new technologies and innovations, the development of resistant biomaterials, a better understanding of knee biomechanics combined with major improvements in intra-operative management. The development of prosthetic implants adapted to each anatomical situation thus optimizes joint kinematics. The number of knee implant surgeries performed annually in France each year is in constant growth and currently estimated at more than 50,000. Degenerative changes in the knee joint resulting from either primary or secondary osteoarthritis are the main indication for knee arthroplasty. The affected population is at risk due to its age (usually over 60 years) and the frequency of associated comorbidities.
Muscle dysfunction (MD) is one of the major complications in patients with chronic obstructive pulmonary disease (COPD). Repercussions on exercise capacity and quality of life can be severe. These guidelines present a summary of the most recent literature published on the various aspects of MD in COPD. The Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) scale has been used to make evidence-based recommendations in this regard. Around one third of COPD patients are estimated to have a 25% loss of quadriceps strength compared to the general population, even in the early stages of the disease. MD affects both the respiratory muscles and, to a lesser extent, the limbs. Various biological factors and mechanisms are involved. Different tests are proposed for evaluating and diagnosing the degree of respiratory and limb muscle impairment, and for determining patients’ exercise capacity (6-minute walk test and cycle ergometry). Current therapeutic strategies comprising different training programs and pharmacological and nutritional support are also evaluated.
A forward trunk lean sometimes occurs to compensate for quadriceps muscle weakness. Since muscle weakness in the lower extremities is commonly observed in the elderly, quadriceps weakness may trigger age-related postural change. The objective of this study was to ascertain the association between forward trunk lean during walking and musculoskeletal strength in females aged between 46 and 79 years. Musculoskeletal functions (range of joint motion, degree of kyphosis, muscle strength) and joint moments during walking were measured for 13 females. Subjects who showed greater joint moments during walking tended to lean more. Moderate association was seen between mean trunk angle during walking and knee extension moment (r = 0.535, p = 0.060). There was no statistically significant correlation between the strength of the quadriceps muscle and the mean trunk angle in walking subjects (r = 0.095, p = 0.758). These observations suggested that muscle weakness in the quadriceps is largely independent of leaning of the trunk for this sample of subjects. Other factors may change the posture to a stoop, such as severe thoracic kyphosis, poor balance control, or fear of falling.
Skeletal muscle fatigue is defined as the fall of force or power in response to contractile activity. Both the mechanisms of fatigue and the modes used to elicit it vary tremendously. Conceptual and technological advances allow the examination of fatigue from the level of the single molecule to the intact organism. Evaluation of muscle fatigue in a wide range of disease states builds on our understanding of basic function by revealing the sources of dysfunction in response to disease. © 2012 American Physiological Society. Compr Physiol 2:997-1044, 2012.
The purpose of this study was to determine optimal stimulation parameters and calculation methods to estimate quadriceps voluntary activation while minimizing participant discomfort. Twelve healthy adults (8 males, 4 females; mean±SD, age=36.8±15.6 years, weight=76.1±12.9 kg, height=170.2±8.6 cm). Repeated maximal volitional isometric contractions (MVIC) were performed while imposing four stimulation combinations (10 pulses or 2 pulses; 400 V or 200 V; and variable current or standardized current) with the quadriceps in a relaxed state (resting twitch (RT)) and during an MVIC. Quadriceps activation was quantified by calculating the central activation ratio and the percent activation. Discomfort was quantified using the visual analog scale (VAS). When comparing calculation methods between the same stimulation parameters the central activation ratio calculation method produced quadriceps activation values that were significantly greater (P< .009) than those derived using the percent activation calculation method. The doublet pulse stimulus produced less discomfort during the RT (P< .04) and MVIC (P< .001) when compared to all other combinations using a train of stimuli (10 pulses). Correlations for all estimates of quadriceps activation were strong (r=.85 to .99, P< .001). A doublet pulse stimulus produced discomfort levels that were over 50% lower than a 10-pulse train of stimuli and correlated well (r>.88) with activation levels obtained with a 10-pulse train of stimuli. Therefore the use of a doublet pulse stimulus provides quadriceps activation information equivalent to other methods while minimizing participant discomfort.
The inflammatory manifestations of knee osteoarthritis (OA) lead to muscle inhibition and hypotrophy, resulting in a reduction in total muscle work and muscle power. Total knee arthroplasty (TKA) is the most adequate surgery for the treatment of advanced OA. However, its effects on muscle functional behavior have not been well understood.
To compare the total work and power of the knee flexor and extensor muscles in patients with OA (20) and in patients post-TKA (12) at two angular velocities (60º/sec and 240º/sec). Methods: An isokinetic Biodex dynamometer was used to assess muscle power and total work during isokinetic contractions. Two-way ANOVA for repeated measures was used to compare total muscle work and muscle power between the groups (SPSS software, version 13.0; significance level, P < 0.05).
There was no difference between the OA and TKA groups for the total work of both knee extensors and flexors at the two angular velocities (P > 0.05). In addition, no difference was observed in the muscle power of the knee extensors and flexors (P > 0.05).
Total work and power were similar in the OA and TKA groups, suggesting that TKA did not improve functional capacity, which was similar in both groups.
Quadriceps weakness and inhibition are impairments associated with patellofemoral pain syndrome (PFPS). Lumbopelvic joint manipulation has been shown to improve quadriceps force output and inhibition, but the duration of the effect is unknown.
To determine whether quadriceps strength and activation are increased and maintained for 1 hour after high-grade or low-grade joint mobilization or manipulation applied at the lumbopelvic region in people with PFPS.
Randomized controlled clinical trial.
University laboratory.
Forty-eight people with PFPS (age = 24.6 ± 8.9 years, height = 174.3 ± 11.2 cm, mass = 78.4 ± 16.8 kg) participated.
Participants were randomized to 1 of 3 groups: lumbopelvic joint manipulation (grade V), side-lying lumbar midrange flexion and extension passive range of motion (grade II) for 1 minute, or prone extension on the elbows for 3 minutes.
Quadriceps force and activation were measured using the burst superimposition technique during a seated isometric knee extension task. A 2-way repeated-measures analysis of variance was performed to compare changes in quadriceps force and activation among groups over time (before intervention and at 0, 20, 40, and 60 minutes after intervention).
We found no differences in quadriceps force output (F(5.33,101.18) = 0.65, P = .67) or central activation ratio (F(4.84,92.03) = 0.38, P = .86) values among groups after intervention. When groups were pooled, we found differences across time for quadriceps force (F(2.66,101.18) = 5.03, P = .004) and activation (F(2.42,92.03) = 3.85, P = .02). Quadriceps force was not different at 0 minutes after intervention (t(40) = 1.68, P = .10), but it decreased at 20 (t(40) = 2.16, P = .04), 40 (t(40) = 2.87, P = .01) and 60 (t(40) = 3.04, P = .004) minutes after intervention. All groups demonstrated decreased quadriceps activation at 0 minutes after intervention (t(40) = 4.17, P < .001), but subsequent measures were not different from preintervention levels (t(40) range, 1.53-1.83, P > .09).
Interventions directed at the lumbopelvic region did not have immediate effects on quadriceps force output or activation. Muscle fatigue might have contributed to decreased force output and activation over 1 hour of testing.
It is well accepted that aging is one of the most prominent risk factors for the initiation and progression of osteoarthritis. One of the most pronounced age-related changes in chondrocytes is the exhibition of a senescent phenotype, which is the result of several factors including the accumulation of reactive oxygen species and advanced glycation end products. Compared with a normal chondrocyte, senescent chondrocytes exhibit an impaired ability to respond to many mechanical and inflammatory insults to the articular cartilage. Furthermore, protein secretion is altered in aging chondrocytes, demonstrated by a decrease in anabolic activity and increased production of proinflammatory cytokines and matrix-degrading enzymes. Together, these events may make the articular cartilage matrix more susceptible to damage and lead to the onset of osteoarthritis. A better understanding of the mechanisms underlying age-related chondrocyte pathophysiology may be critical for the development of novel therapeutic interventions for progressive joint diseases.
The purpose of our study was to determine if aging adults who received rehabilitation following total hip arthroplasty (THA) due to osteoarthritis had better short-term outcomes in an Inpatient Rehabilitation Facility (IRF) compared with those currently receiving rehabilitation in subacute rehabilitation units.
Thirty-six adults, aged 65 to 88 years, who received inpatient rehabilitation following THA secondary to osteoarthritis participated in this study. A prospective descriptive study of 4 aging adults receiving rehabilitation in 2 subacute rehabilitation facilities and a retrospective descriptive study of 32 aging adults who received rehabilitation in an IRF were conducted. Socioeconomic, medical, rehabilitative care, and demographic data were obtained by review of participants' medical charts. FIM scores of the aging adults in the IRF were obtained by chart review, while FIM scores of the aging adults in the subacute facilities were collected by one of the investigators.
In this sample, the aging adults in the IRF appeared to have greater changes in total FIM score, motor subscale FIM score, and self-care subscale FIM score than the aging adults in the subacute facilities. In this sample, discharge setting appeared similar for the aging adults in the two rehabilitation settings.
It is imperative that further research determine if rehabilitation provided in different settings that offer different intensities and durations of rehabilitation affects functional outcomes for aging adults following THA procedures.
Recent studies suggest that the cost of muscle contraction may be reduced in old age, which could be an important mediator of age-related differences in muscle fatigue under some circumstances. We used phosphorus magnetic resonance spectroscopy and electrically elicited contractions to examine the energetic cost of ankle dorsiflexion in 9 young (Y; 26 +/- 3.8 yr; mean +/- SD) and 9 older healthy men (O; 72 +/- 4.6). We hypothesized that the energy cost of twitch and tetanic contractions would be lower in O and that this difference would be greater during tetanic contractions at f(50) (frequency at 50% of peak force from force-frequency relationship) than at 25 Hz. The energy costs of a twitch (O = 0.13 +/- 0.04 mM ATP/twitch, Y = 0.18 +/- 0.06; P = 0.045) and a 60-s tetanus at 25 Hz (O = 1.5 +/- 0.4 mM ATP/s, Y = 2.0 +/- 0.2; P = 0.01) were 27% and 26% lower in O, respectively, while the respective force.time integrals were not different. In contrast, energy cost during a 90-s tetanus at f(50) (O = 10.9 +/- 2.0 Hz, Y = 14.8 +/- 2.1 Hz; P = 0.002) was 49% lower in O (1.0 +/- 0.2 mM ATP/s) compared with Y (1.9 +/- 0.2; P < 0.001). Y had greater force potentiation during the f(50) protocol, which accounted for the greater age difference in energy cost at f(50) compared with 25 Hz. These results provide novel evidence of an age-related difference in human contractile energy cost in vivo and suggest that intramuscular changes contribute to the lower cost of contraction in older muscle. This difference in energetics may provide an important mechanism for the enhanced fatigue resistance often observed in older individuals.
Much attention has been focused on the need to design strategies to increase functional capacities in older populations. This has raised several questions regarding the ability of regular endurance training to preserve functional capacity with age.
The purpose of this study was to examine the age-associated changes in neuromuscular function in endurance-trained men before and after a high-intensity, intermittent fatiguing task.
Twenty-six healthy endurance-trained male subjects: 16 older (59-79 years) and 10 young (20-34 years) men performed a high-intensity, intermittent fatiguing exercise corresponding to 10 sets of 10 repetitions on a horizontal leg press at 70% of the individual one-repetition maximum. Maximal voluntary contractions and evoked contractions of the knee extensor muscles were performed before and after the exercise.
Decreases in maximum voluntary contractions (older: -9.7%; young: -14.3%) and electromyographic activity were not different between groups. Peak twitch torque was reduced only for the older men and no changes in voluntary activation and M-wave properties were recorded in either group.
The present study indicates that in endurance-trained men aged 59-79 years, muscle functional capacities are maintained despite losses in strength and contractile function related to the age.
To examine whether pretreatment magnitude of quadriceps activation (QA) helps predict changes in quadriceps strength after exercise therapy in subjects with knee osteoarthritis (OA). We hypothesized that subjects with lower magnitudes of QA (greater failure of muscle activation) would have smaller gains in strength compared with those with higher magnitudes of QA following exercise therapy.
One hundred eleven subjects with knee OA (70 women) participated. Baseline measures included demographic information, quadriceps muscle strength, and QA using a burst-superimposition isometric torque test. Following baseline testing, subjects underwent a 6-week supervised exercise program designed to improve strength, range of motion, balance and agility, and physical function. On completion of the program, quadriceps strength and QA were reassessed. Multiple regression analysis was used to determine whether baseline QA predicted quadriceps strength scores at the 2-month followup.
Bivariate correlations demonstrated that baseline QA was significantly associated with quadriceps strength at baseline (rho = 0.30, P < 0.01) and 2-month followup (rho = 0.23, P = 0.01). Greater magnitude of baseline QA correlated with higher strength. While controlling for baseline quadriceps strength and type of exercise therapy, the level of QA did not predict quadriceps strength at the 2-month followup (beta = -0.04, P = 0.18).
Baseline QA did not predict changes in quadriceps strength following exercise therapy. Measurement of QA using the central activation ratio method does not appear to be helpful in identifying subjects with knee OA who will have difficulty improving quadriceps strength with exercise therapy.
To determine the central activation and force-frequency properties of a muscle group in which these data have not previously been reported (i.e., the lumbar extensors).
Fifteen young healthy participants were tested. Maximal voluntary isometric contraction (MVIC) of the trunk was collected using a custom apparatus with a cable-mounted load cell. Central activation was determined by delivering a supramaximal 100-ms, 100-Hz train to the lumbar muscles during the MVIC. The MVIC and the stimulated forces were used to calculate the central activation ratio (CAR) for each subject using the formula CAR = MVIC force / (MVIC + stimulated force), with a value of 1 indicating full central activation. Force-frequency relationship of the muscle group was determined by stimulating the muscles every 10 s with two 500-ms trains of the following frequencies: 1, 5, 10, 20, 40, 60, 80, and 100 Hz. The force-frequency data were fit with a four-parameter Hill equation to obtain the frequency at which 50% of the range of forces generated by the various stimulation trains is produced (F50) and the Hill coefficient, which indicates the steepness of the linear portion of the relationship.
Mean MVIC was 345.4 N (SD = 126.7), and mean CAR was 0.95 (SD = 0.06). The force-frequency data showed a mean F50 of 16.40 Hz (SD = 3.15) and a mean Hill coefficient of 2.21 (SD = 0.50).
Central activation and force-frequency testing of the lumbar extensor muscles is feasible, and the data reported here represent, to our knowledge, the first of their kind in this muscle group.
To determine the carboxyhemoglobin (CO-Hb) predictive intervals in active and passive smokers and to obtain an equation expressing the relation of CO-Hb to number of cigarettes smoked, we studied 233 outpatients referred to an urban university hospital for arterial gas measurement. Patients were excluded if they were receiving oxygen therapy or had been hospitalized in the two months before the study. The patients were classified as non smokers (57), passive smokers (54), smokers of less than 11 cigarettes (22), smokers of 11 to 20 (41) smokers of 21 to 40 (44) and smokers of over 40 (15). All patients answered a questionnaire on exposure to tobacco smoke or other sources of CO. Blood gases and co-oximetry were measured in all patients. Mean CO-Hb and 95% confidence intervals were 1.53% (0.78-1.85%) in smokers and 2.59% (1.89-3.29%) in passive smokers. The linear equation that best expressed the relationship was CO-Hb = 0.153 x number of cigarettes + 1.1 exposure to other sources (1 or 0) + 1.39 (SD 0.84)%. Hemoglobin level was significantly higher in the two groups smoking more than 21 cigarettes. We conclude that the predictive intervals is 1.9% in non smokers who are not exposed to other sources of CO. Passive smokers have significantly higher levels of CO-Hb than non smokers. Heavy smokers have polycythemia.
Persistent residual quadriceps femoris muscle force deficits after total knee arthroplasty (TKA) are commonly reported and can prevent patients from returning quickly and fully to functional activities. Neuromuscular electrical stimulation offers a potentially more effective means of increasing muscle force than current rehabilitation protocols.
The patient was a 66-year-old man. Neuromuscular electrical stimulation for increasing quadriceps femoris muscle force was initiated 3 weeks after TKA for 11 sessions to supplement stretching exercises and a high-intensity volitional strengthening program.
The patient's isometric quadriceps femoris muscle force increased from 50% (involved/uninvolved) at 3 weeks after surgery to 86% at 8 weeks after surgery. A concurrent increase in his uninvolved quadriceps femoris muscle force concealed the patient's true increase in his involved quadriceps femoris muscle force in a side-to-side comparison. The patient's final involved quadriceps femoris muscle force (10 weeks after surgery) was 93% of the initial uninvolved quadriceps femoris muscle force.
Our patient was able to return to independent activities of daily living and recreational activities, with force gains that surpassed those reported in the literature.
The purpose of this case problem was to describe an uncommon presentation and treatment of a patient with posterolateral corner instability. Table 1 of the article summarizes the physical therapy interventions and physical therapy goals for this patient. Posterolateral corner damage is typically concomitant with injury to the posterior cruciate ligament (PCL) or anterior cruciate ligament (ACL). This patient was unique because she injured the posterolateral corner in combination with a grade II lateral collateral ligament (LCL) sprain. Additionally, an uncommon feature presenting in this patient's case was the perceived abnormal position of the fibular head. As in most knee injuries, quadriceps weakness was a major contributor to her functional level, thereby making strengthening exercises a cornerstone of treatment. In the clinical management of this patient, reassessment throughout the course of physical therapy, multiplane proprioceptive exercises, and a comprehensive home exercise program (HEP) were h...
Patients with osteoarthritis (OA) of the knee have quadriceps weakness and arthrogenous muscle inhibition (AMI). While total knee arthroplasty (TKA) reliably reduces pain and improves function in patients with knee OA, quadriceps weakness persists after surgery. The purpose of this investigation was to assess contributions of AMI to quadriceps weakness before and after TKA and to assess the effect of pain on AMI.
Twenty-eight patients with unilateral, end-stage, primary knee OA were tested an average of 10 days before and 26 days after TKA. The mean age at time of operation was 63 years (range 49-82 years). Measurements on the involved and uninvolved knees were performed using the burst-superimposition technique, where supramaximal electrical stimulation is superimposed on a voluntary contraction. Knee pain during contraction was measured using a numeric rating scale.
The involved quadriceps were significantly weaker than the uninvolved prior to TKA (p<0.05). Quadriceps strength decreased by 60% (p<0.001) and activation decreased 17% (p<0.001) after TKA. Changes in muscle activation accounted for 65% of the variability in the change in quadriceps strength (r(2)=0.65) (p<0.001). Knee pain during muscle contraction accounted for a small, but significant portion of the change in voluntary activation (r(2)=0.22) (p=0.006).
Exercise regimens that emphasize strong muscle contraction and clinical tools that facilitate muscle activation like biofeedback and neuromuscular electrical stimulation may be necessary to reverse the quadriceps activation failure and weakness in the patients with knee OA that worsens after TKA. The failure of current rehabilitation regimens to directly address activation deficits within the first months after surgery may explain the persistent quadriceps weakness in patients after TKA.
We examined the effect of an age-related leftward shift in the force-frequency relationship on the comparative quadriceps fatigability of nine young (27 ± 1 yr old) and nine old men (78 ± 1 yr old) during low-frequency electrical stimulation. Two different protocols of intermittent trains (6 pulses on, 650 ms off) of electrical stimulation at 25% maximum voluntary contraction were performed by both groups: 1) 180 trains at 14.3 Hz [constant frequency (CF) protocol], and 2) 180 trains at the frequency corresponding to 60% of each subject's force-frequency curve [normalized frequency (NF) protocol; young 14.9 ± 0.4 vs. old 12.7 ± 0.5 Hz; P < 0.05]. The quadriceps of the old men were weaker (-31%) and relaxation was slower compared with the young men, as assessed by the maximal relaxation rate constant of the 50-Hz tetanus (young 12.1 ± 0.2 vs. old 9.2 ± 0.5 s-1; P < 0.05) and a leftward shift in the force-frequency relationship. The NF protocol revealed a decreased fatigability in the quadriceps with old age (percentage of 1st contraction force remaining at 180th: old 63.4 ± 1.5 vs. young 58.2 ± 1.7%; P < 0.05) that was masked during the CF protocol (old 60.7 ± 1.6 vs. young 58.6 ± 2.3%; P > 0.05). Irrespective of the protocol, the maximal relaxation rate was reduced to -73 and -57% of the prefatigue value in the young and old men, respectively. The age-related leftward shift in the force-frequency relationship of the quadriceps contributed to an underestimation of the fatigue resistance with old age during the CF protocol. However, when the stimulation frequency used in the NF protocol was adjusted to account for the age-related shift in the force-frequency relationship, the quadriceps muscles of the old men were less fatigable than those of the young men. Thus we suggest that whole muscle fatigability is better examined by electrical stimulation protocols that are adjusted for inter- and intragroup differences in the force-frequency relationship.
A muscle does not have a unique force-frequency relationship; rather, it is dynamic and depends on the activation history of muscle. The purpose of this study was to investigate the force-frequency relationship of nonfatigued and fatigued skeletal muscle with the use of both catchlike-inducing trains (CITs) that exploited the catchlike property of skeletal muscle and constant-frequency trains (CFTs). Quadriceps femoris muscles were studied during isometric contractions in twelve healthy subjects (5 females, 7 males). Both the peak force and force-time integrals produced in response to each stimulation train were analyzed. Compared with nonfatigued muscles, higher frequencies of activation were needed to produce comparable normalized peak forces when the muscles were fatigued (i.e., a "rightward" shift in the force-frequency relationship) for both the CFTs and the CITs. When using the normalized force-time integral to measure muscle performance, the CFTs required slightly higher frequencies to produce comparable normalized forces from fatigued muscles, but the CITs did not. Furthermore, when the muscles were fatigued, the CITs produced greater peak forces and force-time integrals than all comparable CFTs with frequencies </=20 pps. In general, the lower the frequency the greater the augmentation produced by the CITs. In addition, the CIT that elicited the greatest force-time integral produced a 25% greater force-time integral than the best CFT. Because the CITs augmented forces across a wide range of physiological relevant activation rates, these results may have important clinical implications when using electrical stimulation to aid patients with paralysis. The results of this study contribute to our understanding of the relationship between the activation pattern of a muscle and the force output produced.
The purpose of this study was to identify the changes in the force-frequency relationship (FFR) of the human quadriceps femoris muscle following electrically and voluntarily induced fatigue. Twenty nondisabled subjects each participated in one experimental session to test the effects of electrically induced fatigue on the FFR; 10 of these subjects participated in a second session in which voluntarily induced fatigue was produced. Fatigue was induced by having subjects perform repeated, 8-second, isometric contractions followed by 12-second rests until 50% of the initial force was produced. Markedly decreased forces were seen at all frequencies tested following fatigue. Low frequency fatigue was observed following both fatiguing protocols. The frequencies needed to produce near-maximum forces did not shift with fatigue. These results suggest that the most appropriate stimulation frequency to use when activating skeletal muscle depends on both the percentage of tetanic force desired and the fatigue state of the muscle. This study also provides the clinician with data on the FFR of healthy human quadriceps femoris muscle prior to fatigue. [Binder-Macleod SA, McDermond LR. Changes in the force-frequency relationship of the human quadriceps femoris muscle following electrically and voluntarily induced fatigue.
With increasing age, human skeletal muscles gradually decrease in volume, mainly due to a reduced number of motor units and muscle fibers, and a reduced size of type 2 fibers. As a result, progressive weakening and impaired mobility occur. High-resistance strength training is beneficial, even in the very old, and could possibly reverse some of the detrimental effects of age-related weakness. The importance of exercise for older people affords an excellent opportunity for the medicine community as a major source of information and promotion of physical activity for this rapidly growing segment of the population. In this review, we summarize the current knowledge of the effects of aging on the human neuromuscular system, describe some of the major underlying mechanisms of the aging atrophy and focus on the importance of strength training to improve muscle function in older people.
Muscle fatigue can be defined as a decrease in the force-generating ability of a muscle that resulted from recent activity. Recent studies of muscle fatigue are reviewed that are relevant to two areas of interest to physical therapists: clinical assessment of muscle fatigue and neuromuscular electrical stimulation. Volitional and electrical tests have been used to quantify muscle fatigue. Several variations on each type of test are discussed, as are the possible sites in which fatigue might occur. The rate of fatigue during the therapeutic application of electrical stimulation of skeletal muscle is much greater than that seen during volitional contractions. Factors contributing to this phenomenon are examined. The unique requirements affecting how stimulus variables can be manipulated to minimize muscle fatigue in three specific therapeutic uses of neuromuscular electrical stimulation are addressed.
The effects of increasing age on skeletal muscle fatigue and endurance were assessed in 22 healthy young (14 men and 8 women;
mean age, 28 ± 6 years) and 16 healthy old (8 men and 8 women; mean age, 73 ± 3 years) individuals. All subjects performed
100 repeated maximum dynamic knee extensions at 90° · s−1 (1.57 rad·s−1) using an isokinetic dynamometer (Cybex 11). Peak torque was recorded during every contraction, and for each individual the
maximal voluntary contraction (MVC), the fatigue rate, the endurance level, and the relative reduction in muscle force were
determined. MVC and endurance level were significantly lower in old men and women, but there was no discernible difference
in relative muscle force reduction and fatigue rate between young and old individuals. We conclude that thigh muscles of older
individuals are weaker than those of younger individuals, but relative to their strength, older individuals have similar properties
as younger individuals with respect to muscle fatigue and endurance.
Because some of the decline in strength with age may be explained by an impairment of muscle activation, the purpose of this study was to determine the activation level achieved in biceps brachii by older adults during a maximum voluntary contraction (MVC). This capability was assessed with two superimposition techniques: one calculated the activation level that was achieved during an MVC, and the other provided an estimate of the expected MVC force based on extrapolation with submaximal forces. The activation level in biceps brachii was incomplete (< 100%) for the young (n = 16) and elderly (n = 16) subjects, with the elderly subjects exhibiting the greater deficit. In contrast, there was no difference between the measured and expected MVC forces for either group of subjects, whether the extrapolation involved a third-order polynomial or linearization of the data. Because of the lower signal-to-noise ratio associated with the measurement of activation level and the greater number of measurements that contributed to the estimate of the expected MVC force, we conclude that the older adults were able to achieve complete activation of the biceps brachii muscle during an MVC.
(1) To determine the importance of quadriceps strength, structural change, and psychological status in terms of knee pain in the community. (2) To determine the relative importance of quadriceps function, structural change, and psychological status with respect to disability in subjects with knee pain.
300 men and women with pain and 300 controls without pain (aged 40-79) were seen. Isometric quadriceps strength (MVC) was measured and muscle activation was assessed by twitch superimposition. Disability (Western Ontario McMaster Osteoarthritis Index (WOMAC)) and anxiety and depression were assessed (Hospital Anxiety and Depression Index (HAD)). Radiographs were obtained of the tibiofemoral and patellofemoral joints and total score for osteophyte, narrowing, and sclerosis calculated for each knee.
Subjects with knee pain had lower voluntary quadriceps strength than those without pain (p < 0.005). Quadriceps activation was also lower (p < 0.005), but did not fully explain the reduction in strength. When analysed by multiple logistic regression: quadriceps strength (odds ratio 18.8, CI 4.8, 74.1 for MVC < or = 10 kgF); depression (odds ratio 2.4, CI 1.0, 5.5 for HAD score > or = 8); and radiographic change (odds ratio 4.1, CI 1.9, 8.6 for radiographic score > or = 4) were independently associated with pain. In those with knee pain, disability was independently associated with quadriceps strength (odds ratio 8.2, CI 1.5, 44.4 for MVC < or = 10 kgF) and depression (odds ratio 6.2, CI 2.1, 18.0 for HAD score > or = 8); but not with radiographic score.
Quadriceps strength is strongly associated with knee pain and disability in the community, even when activation and psychological factors are taken into account. This has important therapeutic implications.
Voluntary muscle strength declines significantly in older adults. One contributing factor to the strength loss is muscle atrophy developed in old age. Whether the ability to maximally activate the muscle decreases with age, however, is unknown. This study was intended to determine if the central nervous system command to maximally activate the biceps brachii muscle deteriorates with age.
Electrical stimulation pulses were applied to the skin overlying the biceps brachii muscle during maximal voluntary elbow-flexion contractions. The magnitude of force evoked on the maximal voluntary force was measured to determine the activation level (AL) of the muscle.
The AL was 94% for the elderly group and 97% for the young group (100% AL indicates complete activation). The AL for both the elderly and young groups was significantly (p<.05) lower than 100%. The AL of the elderly group was significantly (p<.05) lower than that of the young group.
The loss of voluntary strength in older adults is a mixed result of muscle atrophy and a reduced ability to fully activate muscle.
This review focuses on the functional relationship between age-related morphological and physiological changes at the level of the motor unit (MU). It is well established that older humans are weaker than younger people, exhibit reduced force control, and have slower neuromuscular contractile properties. Older people may also exhibit a decrease in MU discharge rate, and an increase in variability of MU discharge at high force levels. The matching of MU discharge and contractile properties may be an age-related neurophysiological strategy adopted to optimize motor control, similar to that observed in acute conditions such as fatigue. Because muscle force output is modulated partially by MU discharge behavior, the study of these properties may offer insights into the physiology of muscular weakness and motor function in older people. In turn, this will allow the implementation of optimal exercise and rehabilitation programs to reduce the degree of dependence associated with aging. © 1997 John Wiley & Sons, Inc. Muscle Nerve, 20, 679–690, 1997.
The purpose of this investigation was to examine the integrity of neuromuscular transmission and impulse propagation during fatigue by examining the muscle compound action potential (M wave) in elderly and young adults. The tibialis anterior muscle of nine elderly [mean = 67.7 (SE 1.7) years] and nine young [mean = 26.7 (SE 1.2) years] adults was maximally stimulated repetitively at frequencies of 20, 30 or 40 Hz for 60 s on separate occasions. There was a significantly smaller resting M wave amplitude [7.9 (SE 0.4) mV versus 9.9 (SE 0.6) mV] and M wave area [0.038 (SE 0.005) mV s versus 0.06 (SE 0.004) mV.s] in the elderly versus the young adults respectively. Measurement of the evoked muscle contractile properties revealed significantly (P < 0.05) longer twitch durations and a significantly (P < 0.05) greater peak twitch torque [4.6 (SE 0.4) Nm versus 3.2 (SE 0.5) Nm] in the elderly versus the young adults, respectively. The elderly adults had a significantly greater torque decline during the 20-Hz trial; however, the decline in torque during the 30-Hz and 40-Hz trials was similar in the elderly and the young adults (30 Hz: 40%; 40 Hz: 56%). Throughout each of the stimulation trials, the decline in torque was accompanied by a significant reduction in M wave amplitude (20 Hz: 14%; 30 Hz: 53%; 40 Hz: 67%); M wave area also declined significantly during the 30-Hz (31%) and 40-Hz (53%) trials. There was no significant difference between the elderly and the young adults in the reduction in the M wave amplitude or area during each trial.(ABSTRACT TRUNCATED AT 250 WORDS)
The effect of aging on the voluntary and electrically evoked contractile properties of the human adductor pollicis muscle was investigated in 70 healthy male subjects aged 20-91 yr, 10 subjects for each decade. Maximum isometric voluntary force declined significantly (range of P values less than 0.001-0.05) after the age of 59 yr, dropping by the eighth decade to 57.6% of the level recorded in the second decade. A significant shift (P range less than 0.001-0.05) to the left of the frequency-force curve after ulnar nerve supramaximal stimulation at 1, 10, 20, 30, and 50 Hz was observed in the most elderly group (greater than 80 yr) compared with the youngest group (20-29 yr). Maximum relaxation rate dropped by 48.7% from the second to the eighth decade. The decrease became significant (P range less than 0.05-0.001) with the sixth decade. Isometric endurance, evaluated during 30 s of stimulation at 30 Hz, showed a linear (P less than 0.001) increase with age. Aged muscle is thus weaker, slower, and tetanized at lower fusion frequencies but, paradoxically, more resistant to static fatigue.
The 24 h recovery pattern of contractile properties of the triceps surae muscle, following a period of muscle fatigue, was compared in physically active young (25 years,n = 10) and elderly (66 years,n = 7) men. The fatigue test protocol consisted of 10 min of intermittent submaximal 20 Hz tetani. The maximal twitch (p
t) and tetanic force at 3 frequencies (10, 20 and 50 Hz) were determined at baseline and at 15 min, 1, 4 and 24 h after fatiguing the muscle. Maximal voluntary contraction (MVC) and vertical jump (MVJ) were also assessed. The loss of force during the fatigue test was not significantly different between the young (18±13%) and elderly (22±15%). Both groups showed similar and significant reductions of Pt (15%), tetanic force (10 to 35%) and rate of force development (dp/dt) (20%) 15 min and 1 h into recovery. The loss of force was greater at the lower stimulation frequencies of 10 and 20 Hz. Time-to-peak tension was unchanged from baseline during recovery in either group. The average rate of relaxation of twitch force (−dPt/dt) was decreased (p<0.05) and half-relaxation time significantly increased at 15 min and 1 h in the elderly but not the young. The findings indicate that after fatiguing contractions, elderly muscle demonstrates a slower return to resting levels of the rate and time course of twitch relaxation compared to the young.
The electrically evoked isometric properties of the triceps surae have been studied in young (22 yr) and elderly (69 yr) men and women. The results show that the triceps surae of elderly subjects had an increased time to peak tension (TPT) of the twitch, a lower specific tension (force/cross section area), and showed a greater relative force loss when subjected to a standard "fatigue" test procedure than young triceps surae. The respective figures for TPT, specific tension, and fatigue index (FI) were 147 +/- 15 ms (male), 143 +/- 8 ms (female), 19.5 N/cm2 and 0.52 +/- 0.16 (male), 0.37 +/- 0.09 (female) in the elderly, compared with 118 +/- 14 ms (male), 132 +/- 11 ms (female), 32.9 N/cm2 and 0.67 +/- 0.11 (male), 0.62 +/- 0.09 (female) in their younger counterparts. The peak rates of rise (delta P50, delta P200) and relaxation (delta PR50, delta PR200) of tetani at 50 Hz and 200 Hz were slower (p less than 0.05) in the elderly group. The delta P50 and delta P200 were inversely associated (r = 0.76 and -0.50 respectively) with TPT, and the half relaxation time (1/2RT) of the maximal twitch was related to delta PR50 (r = 0.53). The decrease of tetanus relaxation rate during the 2 min fatigue test (delta PRF) was greater in the elderly than the young and was positively associated (r = 0.74) with FI. It is concluded that elderly muscle is weaker, more slowly contracting and fatigable than that of the young. However, it is suggested that the reduced specific tension and enhanced fatiguability of the elderly may in part be due respectively to the inadequacies of our estimates of the effective cross-sectional area CSA) of contractile tissue in the lower leg and the influence of blood flow which may be compromised during a 2 min test.
The effects of aging on maximal voluntary strength and on the isometric twitch were determined in the ankle dorsiflexor and plantarflexor muscles of 111 healthy men and women aged 20-100 yr. Men were found to be stronger than women at all ages. In both sexes, the average values for maximum voluntary strength of the dorsiflexors and plantarflexors began to decline in the 6th decade. Although the absolute loss of strength was greater for the plantarflexor muscles, the relative losses were similar in the two muscle groups. During maximum voluntary effort, stimulation of motor nerves produced no additional torque in the majority of elderly men and women, indicating that these subjects remained able to utilize their descending motor pathways for optimal muscle activation. Comparisons of muscle compound action potentials, twitch torques, and muscle cross-sectional areas suggested that a decrease in excitable muscle mass was entirely responsible for the lower strength of the elderly. An additional effect of aging was the gradual prolongation of twitch contraction and half-relaxation times throughout the adult life-span.
Two different methods for estimating muscle function were compared; hand grip strength (HGS) and adductor pollicis muscle function after electrical stimulation of the ulnar nerve. Fifty-two 'normal' subjects, who were divided into four groups, according to sex and age, were investigated. Technical modifications of the latter method are presented for the measurement of human skeletal muscle function, independent of the motivation of the subject. Maximal voluntary force, as measured with a hand dynamometer, was higher in males than in females. Young males were stronger than males over 50 years old, and young females were stronger than old women. The statistical analysis of the muscle function variables after electrical stimulation showed that young females developed relatively more force at low stimulating frequencies than females over 50 years old. Females had a significantly longer contraction time to tetany compared to males. The relaxation rate after tetanic stimulation was independent of sex and age. Endurance was reduced in old males compared to females in the same age-group and to young males.
The factors limiting force production and exercise endurance time have been briefly described, together with some of the changes occurring at various sites within the muscle and central nervous system. Evidence is presented that, in fatigue of sustained maximal voluntary contractions (MVC) executed by well-motivated subjects, the reduction in force generating capacity need not be due to a decline in central nervous system (CNS) motor drive or to failing neuromuscular transmission, but can be attributed solely to contractile failure of the muscles involved. However, despite this conclusion, both the integrated electromyogram (EMG) and the mean firing rate of individual motor units do decline progressively during sustained MVC. This, however, does not necessarily result in loss of force since the parallel slowing of muscle contractile speed reduces tetanic fusion frequency. It is suggested that the range of motoneuron firing rates elicited by voluntary effort is regulated and limited for each muscle to the minimum required for maximum force generation, thus preventing neuromuscular transmission failure and optimizing motor control. Such a CNS regulating mechanism would probably require some reflex feedback from the muscle.
Effects of progressive heavy resistance strength training combined with explosive types of exercises for 12 weeks on electromyographic activity (EMG), muscle cross-sectional area of the quadriceps femoris (QF), isometric maximal force and force-time curve of the leg extensor muscles were investigated in 9 middle-aged males and 9 females in the 50-year age group (M50; range 44-57), (F50; range 43-54), and in 10 elderly males and 11 females in the 70-year age group (M70; range 64-73), (F70; range 66-73). Great gradual increases took place in maximal force during the 12-week training period both in M50 (from 2834 +/- 452 N to 3941 +/- 772 N; p < 0.001) and in F50 (from 2627 +/- 725 N to 3488 +/- 1017 N; p < 0.001) as well as in M70 (from 2591 +/- 736 N to 3075 +/- 845 N; p < 0.01) and in F70 (from 1816 +/- 427 N to 2483 +/- 408 N; p < 0.001). Significant (p < 0.05-0.001) increases occurred also in the maximum integrated EMGs of the trained muscles in all groups primarily during the first 8 weeks of the training. Significant (p < 0.05-0.001) enlargements took place during the 12-week training period in the CSA of the QF muscle in all groups. Significant (p < 0.05-0.001) shifts occurred in all groups in the shape of the absolute force-time curves and the maximal rate of force production increased (p < 0.05-0.001) during the training as well. The present findings suggest that progressive heavy strength training combined with explosive types of exercises may lead to considerable increases not only in maximal strength but also in explosive force production characteristics of the trained muscles accompanied by adaptations in the nervous system as well as by muscular hypertrophy not only in middle-aged but in elderly males and females as well.
Quadriceps femoris muscles were studied in 50 healthy subjects to determine the physiological responses of the motor units recruited at different force levels during transcutaneous electrical stimulation. During one set of experiments force-frequency relationships were compared at stimulation intensities that produced tetanic contraction of 20%, 50%, or 80% of the maximum voluntary isometric contraction (MVC). No differences in the normalized force-frequency relationship were observed between the 20% and 50% of MVC conditions and only a slight shift to the left was observed at 80% of MVC. The other set of experiments measured the responses to electrically elicited fatigue tests using frequencies of 20, 40, or 60 pps and, at each frequency, intensities that produced 20% or 50% of MVC. Fatigue was greater for the 50% than 20% MVC force conditions. Within each force level fatigue increased with increasing frequency. However, though the differences in the level of recruitment needed to produce the two forces varied for each frequency, the differences in the amount of fatigue produced at each force did not vary between the three stimulation frequencies. This suggests that the fatigue characteristics of the recruited motor units were similar at all intensities tested. We posit, therefore, that the physiological recruitment order during transcutaneous electrical stimulation is less orderly than previously suggested.
A burst-superimposition technique was used to assess the strength of the quadriceps femoris muscle in three groups of patients. Group 1 comprised twenty patients who had had a torn anterior cruciate ligament of the knee and had a reconstruction of the ligament one to six months after the injury. Group 2 comprised twelve patients who had had a torn anterior cruciate ligament for an average of three months (a subacute tear). Group 3 comprised eight patients who had had a torn anterior cruciate ligament for an average of two years (a chronic tear). The patients in Groups 2 and 3 had not had an operation for the torn ligament. The patients in Groups 1 and 3 had no evidence of failure of activation of the involved quadriceps, but nine of the twelve patients in Group 2 had reflex inhibition of contraction of the muscle.
Aging skeletal muscle exhibits decreases in muscle mass and force and changes in contractile properties. The effects of aging on the physiological characteristics of skeletal muscle are fiber type specific. This review describes the aging process in skeletal muscle; specifically, the effects of aging on the biochemical, morphological, and physiological characteristics of type I (slow-twitch) fibers and type II (fast-twitch) fibers. The effects of training on specific fiber types are also reviewed. The age-related decrease in maximum isometric force may be due, in part, to a decline in muscle mass. Decreases in muscle mass appear to occur in weight-bearing muscles and are most marked in those with a high proportion of type II fibers. The age-related fiber atrophy contributes to the decline in muscle mass. The decline in fiber size is prominent in type II fibers, whereas type I fibers are less affected. The age-related prolongation in isometric twitch properties may be due, in part, to alteration in the capacity of the sarcoplasmic reticulum for calcium release and recapture. Resistance and endurance training appear to attenuate the age-related alterations in skeletal muscle properties if the stimulus is of a sufficient intensity and duration.
The responses of quadriceps femoris muscles to an electrically elicited fatigue test were recorded from both lower extremities of 18 patients who had recently undergone unilateral, anterior cruciate ligament reconstruction. The fatigue test consisted of 40 pps, 13-pulse electrical trains that were repeated once per second for 3 min. The intensity of stimulation was set for each extremity to produce 20% of the maximum voluntary isometric contraction of the uninvolved muscle. The uninvolved quadriceps femoris muscle showed a significantly greater rate of decline in force over the first minute than the involved muscle (0.803%.s-1 for uninvolved muscle vs 0.620%.s-1 for involved muscle). Similarly, the average forces produced over the last minute were significantly lower for the uninvolved than the involved quadriceps femoris muscle (uninvolved = 42.6%, involved = 50.4% of their original forces). These surprising results showed that the involved quadriceps femoris muscles were more endurant than the uninvolved muscles. It is suggested that the increases in endurance of the involved muscle may have been due, in part, to greater recruitment of Type I fibers with electrical stimulation or selective Type II fiber atrophy in the involved muscle.
Reflex arthogenous muscle inhibition (AMI) may cause muscle atrophy or impede effective rehabilitation of affected muscle
groups. To investigate this, bilateral quadriceps AMI, isometric and isokinetic muscle strength were measured in 10 patients
with unilateral osteoarthritic knees, before and after a course of routine physiotherapy. Before rehabilitation, quadriceps
of all the diseased legs were inhibited (P<0.05) and 40% weaker (P<0.02) than the non-diseased legs. Following rehabilitation,
AMI decreased (P<0.01) in the diseased leg and strength increased at all test velocities (P<0.05–0.005); however, strength deficits compared with the non-diseased leg remained. Subjective improvements in functional
ability and confidence in the diseased leg were reported. Though AMI may be partially responsible for unilateral muscle weakness,
it does not preclude strength gain in affected muscles. Possible physiological mechanisms which evoke AMI may also adversely
affect muscle proprioception, implicating AMI as a possible cause of initiation or progression of degenerative joint disease.
As humans age, there is a decrease in the ability of skeletal muscle to generate force. This review describes alterations in the neuromuscular systems of humans and animals that may be responsible for the diminished force-generating capacity of older muscles. The effects of resistance training on the force-generating capacity of older muscles in humans and on the neuromuscular systems of humans and animals are then examined. The age-related decline in force-generating capacity may be due, in part, to a loss of motor units and to a decline in muscle mass. Fiber atrophy and, possibly, loss of muscle fibers contribute to the decline in muscle mass in older persons. High-intensity resistance training appears to attenuate the age-related decline in force-generating capacity in humans and cause fiber hypertrophy of old muscle fibers. Investigations of the effects of age on the neuromuscular system and of the effects of resistance training on the neuromuscular system and the functional capacity of older persons are essential for the development of cost-effective interventions that will increase the physical capacity of older persons.
1. Voluntary activation of elbow flexor muscles can be optimal during brief maximal voluntary contractions (MVCs), although central fatigue, a progressive decline in the ability to drive the muscle maximally, develops during sustained or repeated efforts. We stimulated the motor cortex and motor point in human subjects to investigate motor output during fatigue. 2. The increment in force (relative to the voluntary force) produced by stimulation of the motor point of biceps brachii increased during sustained isometric MVCs of the elbow flexors. Motoneuronal output became suboptimal during the contraction, i.e. central fatigue developed and accounted for a small but significant loss of maximal voluntary force. During 3 min MVCs, voluntary activation of biceps fell to an average of 90.7% from an average of > 99%. 3. The increment in force (relative to the voluntary force) produced by magnetic cortical stimulation was initially small (1.0%) but also increased during sustained MVCs to 9.8% (with a 2 min MVC). Thus, cortical output was not optimal at the time of stimulation nor were sites distal to the motor cortex already acting maximally. 4. A sphygmomanometer cuff around the upper arm blocked blood supply to brachioradialis near the end of a sustained MVC and throughout subsequent brief MVCs. Neither maximal voluntary force nor voluntary activation recovered during ischaemia after the sustained MVC. However, fatigue-induced changes in EMG responses to magnetic cortical stimulation recovered rapidly despite maintained ischaemia. 5. In conclusion, during sustained MVCs, voluntary activation becomes less than optimal so that force can be increased by stimulation of the motor cortex or the motor nerve. Complex changes in excitability of the motor cortex also occur with fatigue, but can be dissociated from the impairment of voluntary activation. We argue that inadequate neural drive effectively 'upstream' of the motor cortex must be one site involved in the genesis of central fatigue.
Muscle fatigue or neuromuscular disease may result in central activation failure during maximal voluntary contractions (MVCs). Superimposition of an electrically stimulated contraction during an MVC has been used to detect central activation failure. To determine the most sensitive means of quantitating central activation failure using this technique, we compared the increment in isometric force from single, double, and high-frequency trains (50 Hz, 500 or 1000 ms) of stimuli of the peroneal nerve imposed during three separate MVCs of the dorsiflexor muscles. Completeness of activation was quantitated with the central activation ratio (CAR) = MVC/(MVC + stimulated force). Comparisons were made of the CARs of three groups of subjects during the three stimulation conditions: 7 healthy subjects, 13 patients with amyotrophic lateral sclerosis, and 5 healthy subjects after fatiguing exercise. For all three groups, the CAR was significantly lower during the train of stimuli condition (means = 0.76-0.89) compared with either the single or double stimuli conditions (means = 0.96-1.00). The results suggest that a superimposed high-frequency train of stimuli is a more sensitive indicator of central activation failure during isometric MVCs compared with either the superimposed single or double stimuli methods.
This review focuses on the functional relationship between age-related morphological and physiological changes at the level of the motor unit (MU). It is well established that older humans are weaker than younger people, exhibit reduced force control, and have slower neuromuscular contractile properties. Older people may also exhibit a decrease in MU discharge rate, and an increase in variability of MU discharge at high force levels. The matching of MU discharge and contractile properties may be an age-related neurophysiological strategy adopted to optimize motor control, similar to that observed in acute conditions such as fatigue. Because muscle force output is modulated partially by MU discharge behavior, the study of these properties may offer insights into the physiology of muscular weakness and motor function in older people. In turn, this will allow the implementation of optimal exercise and rehabilitation programs to reduce the degree of dependence associated with aging.
Muscle strength, activation, and size were studied in 11 very elderly subjects (8 women and 3 men; age range, 85-97 years) who completed 12 weeks of strength training of the knee extensor muscles. Training increased the maximum amount of weight that could be lifted once (134%; P < 0.05) and maximum voluntary isometric strength, measured as both force recorded at the ankle with the knee flexed 90 degrees (17%, ns) and as torque with the knee flexed 60 degrees (37%; P < 0.05). Anatomical lean quadriceps cross-sectional area (LCSA) measured at midthigh using magnetic resonance imaging increased from 27.5 +/- 9.6 cm2 to 30.2 +/- 10.0 cm2 (9.8%; P < 0. 05) after training. Both before and after training, isometric strength was closely related to LCSA, but training resulted in no significant change in muscle force per unit area of quadriceps muscle. Using the twitch interpolation technique, muscle activation during a maximal voluntary isometric contraction was shown to be incomplete in all subjects before training (ranging from 69% to 93%) and was not significantly increased after training. An increase in skeletal muscle mass may have important functional and metabolic benefits for very elderly people.
The extents to which decreased muscle size or activation are responsible for the decrease in strength commonly observed with aging remain unclear. Our purpose was to compare muscle isometric strength [maximum voluntary contraction (MVC)], cross-sectional area (CSA), specific strength (MVC/CSA), and voluntary activation in the ankle dorsiflexor muscles of 24 young (32 +/- 1 yr) and 24 elderly (72 +/- 1 yr) healthy men and women of similar physical activity level. Three measures of voluntary muscle activation were used: the central activation ratio [MVC/(MVC + superimposed force)], the maximal rate of voluntary isometric force development, and foot tap speed. Men had higher MVC and CSA than did women. Young men had higher MVC compared with elderly men [262 +/- 19 (SE) vs. 197 +/- 22 N, respectively], whereas MVC was similar in young and elderly women (136 +/- 15 vs. 149 +/- 16 N, respectively). CSA was greater in young compared with elderly subjects. There was no age-related impairment of specific strength, central activation ratio, or the rate of voluntary force development. Foot tap speed was reduced in elderly (34 +/- 1 taps/10 s) compared with young subjects (47 +/- 1 taps/10 s). These results suggest that isometric specific strength and the ability to fully and rapidly activate the dorsiflexor muscles during a single isometric contraction were unimpaired by aging. However, there was an age-related deficit in the ability to perform rapid repetitive dynamic contractions.
Changes with age in the voluntary static and dynamic strength of the quadriceps muscle group have been well characterized, and the importance of the muscle group for locomotion and independent living have been highlighted in both normal human aging and in clinical studies. Surprisingly few studies of this muscle group have described age-related changes in voluntary activation ability using twitch interpolation and changes in stimulated contractile properties, and none have assessed the influence of old age on motor unit firing rates. We compared in 13 young (mean age 26 years) and 12 old (mean age 80 years) men the voluntary isometric strength, stimulated contractile properties, and average steady state motor unit firing rates in the quadriceps muscle. Maximum voluntary contraction (MVC) force and twitch tension were approximately 50% lower in the old men, but contractile speed was only approximately 10% slower than in the young men. There was no difference in the ability of either group to activate the quadriceps to a high degree (94-96%). At all isometric force levels tested (10%, 25%, 50%, 75%, and 100% MVC), there were no differences in mean motor unit firing rates. In both groups, the range of firing rates was similar and not large ( approximately 8 Hz at 10% MVC and 26 Hz at MVC). Thus, the substantial age-related weakness in this muscle does not seem to be related to changes in neural drive.
Quadriceps weak-ness in knee osteoarthritis: the effect on pain and disability Suppliers a. Kin-Com III force dynamometer
- O Reilly
- Jones A Sc
- Kr Muir
- Doherty
O'Reilly SC, Jones A, Muir KR, Doherty M. Quadriceps weak-ness in knee osteoarthritis: the effect on pain and disability. Ann Rheum Dis 1998;57:588-94. Suppliers a. Kin-Com III force dynamometer; Chattanooga Corp, 4717 Adams Rd, Hixson, TN 37343.
Bar-tolozzi AR. Reflex inhibition of the quadriceps femoris muscle after injury or reconstruction of the anterior cruciate ligament
- Snyder
- L Mackler
- Deluca
- Williams Pr Pf
- Eastlack
- Me
Snyder-Mackler L, DeLuca PF, Williams PR, Eastlack ME, Bar-tolozzi AR. Reflex inhibition of the quadriceps femoris muscle after injury or reconstruction of the anterior cruciate ligament. J Bone Joint Surg Am 1994;76:555-60.
The control of movement
- C Ghez
- Er Kandel
- Schwartz
Ghez C. The control of movement. In: Kandel ER, Schwartz JH, Jessel TM, editors. Principles of neural science. Englewood Cliffs (NJ): Prentice Hall; 1991. p 542-3.
Maximum voluntary recruitment in fresh and fatigued muscle of young and elder individuals [abstract]
- Lee
- Pearce Km Sc
- Snyder
- L Mackler
- Binder-Macleod
- Sa
Lee SC, Pearce KM, Snyder-Mackler L, Binder-Macleod SA. Maximum voluntary recruitment in fresh and fatigued muscle of young and elder individuals [abstract]. FASEB J 1999;13:A690.
The control of movement
- Ghez
Knee extensor strength, activation, and size in very elderly people following strength training
- Harridge
Maximum voluntary recruitment in fresh and fatigued muscle of young and elder individuals [abstract]
- Lee