No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Changes in Lifting Dynamics after Localized Arm Fatigue
Abstract
The purposes of this study were (1) to compare the lifting strategies during arm fatigue and non-fatigue conditions and (2) to evaluate the effects of localized arm fatigue on L5/S1 compressive forces during lifting. The hypothesis was that isometrically induced arm fatigue can alter the lifting strategy selection resulting in an increase in the initial acceleration and leading to an increase in lower back stress. Biomechanical analyses of lifting were done before and after the performance of holding activity to induce arm muscle fatigue, Differences in the lifting strategies used including the accelerated effect, pre-lifting technique, and stiffening of the arms were monitored to determine their influence on L5/S1 compressive forces under various load and range conditions. The results show that lifting strategy changed significantly after arm fatigue, especially when the load was less than 20 kg. These changes included the use of increasingly stooped and accelerated techniques adopted at the beginning of the lift and stiffening of the arms at the end of the lift. Arm fatigue resulted in increased compressive forces at the L5/S1 disc due to the use of accelerated techniques and the inherent disadvantage of these techniques in the pre-lifting posture. In this study, lifting strategies changed as a function of arm fatigue, resulting in increased lower back loading. These findings suggest that whole-body lifting should be avoided after localized arm fatigue in order to decrease the risk of injury to the lower back.
... Optimal movement variations are recognized as factors delaying the development of fatigue during a prolonged activity (Bartlett et al., 2007;Sedighi & Nussbaum, 2017;Srinivasan & Mathiassen, 2012) by distributing load across active-passive tissues, thus maintaining performance (Bauer et al., 2017;van Dieën et al., 2003). Depending on the region and extent of fatigue, various behavioral changes have been observed including lifting style, switching between stoop and squat postures (Bonato et al., 2003), and accelerated forward bending (Bernardo et al., 2018;Chen, 2000). ...
... In these studies and other similar studies focused only on kinematic measures (Fischer et al., 2015;Mehta et al., 2014), adaptations during the course of lifting were neglected and comparisons were limited to the initial and last parts of the task. It is also worthwhile to note that changes in the lifting strategy impact the movement of the hand load and result in varying levels of compressive force (Fc) at the L5-S1 disc (Chen, 2000). However, cycle-by-cycle changes in the Fc at the L5-S1 disk have been overlooked in the previous studies. ...
... A key point, which is also neglected, is that repetitive lifting is a complex dynamic task (Chen, 2000) with nonlinear dynamical properties of biomechanical responses (Khalaf et al., 2015). Recent research evidence supports the fact that linear measures quantify the magnitude of variation in a series of data irrespective of their order in the distribution. ...
Objective
Spine kinematics, kinetics, and trunk muscle activities were evaluated during different stages of a fatigue-induced symmetric lifting task over time.
Background
Due to neuromuscular adaptations, postural behaviors of workers during lifting tasks are affected by fatigue. Comprehensive aspects of these adaptations remain to be investigated.
Method
Eighteen volunteers repeatedly lifted a box until perceived exhaustion. Body center of mass (CoM), trunk and box kinematics, and feet center of pressure (CoP) were estimated by a motion capture system and force-plate. Electromyographic (EMG) signals of trunk/abdominal muscles were assessed using linear and nonlinear approaches. The L5-S1 compressive force (Fc) was predicted via a biomechanical model. A two-way multivariate analysis of variance (MANOVA) was performed to examine the effects of five blocks of lifting cycle (C1 to C5) and lifting trial (T1 to T5), as independent variables, on kinematic, kinetic, and EMG-related measures.
Results
Significant effects of lifting trial blocks were found for CoM and CoP shift in the anterior–posterior direction (respectively p < .001 and p = .014), trunk angle ( p = .004), vertical box displacement ( p < .001), and Fc ( p = .005). EMG parameters indicated muscular fatigue with the extent of changes being muscle-specific.
Conclusion
Results emphasized variations in most kinematics/kinetics, and EMG-based indices, which further provided insight into the lifting behavior adaptations under dynamic fatiguing conditions.
Application
Movement and muscle-related variables, to a large extent, determine the magnitude of spinal loading, which is associated with low back pain.
... It is believed fatigue may induce manipulations to lifting technique (Sakamoto & Sinclair, 2006), however few studies have examined these effects. Chen (2000) found lifting strategies to be altered following arm fatigue, which resulted in higher L5/S1 compression forces (Chen, 2000). The authors suggest altered lifting mechanics may put individuals at a greater risk for injury during fatigued conditions (Chen, 2000). ...
... It is believed fatigue may induce manipulations to lifting technique (Sakamoto & Sinclair, 2006), however few studies have examined these effects. Chen (2000) found lifting strategies to be altered following arm fatigue, which resulted in higher L5/S1 compression forces (Chen, 2000). The authors suggest altered lifting mechanics may put individuals at a greater risk for injury during fatigued conditions (Chen, 2000). ...
... Chen (2000) found lifting strategies to be altered following arm fatigue, which resulted in higher L5/S1 compression forces (Chen, 2000). The authors suggest altered lifting mechanics may put individuals at a greater risk for injury during fatigued conditions (Chen, 2000). With regards to resistance exercise, Duffey and Challis (2007) examined the effects of fatigue on bench press kinematics and found lifters to keep the barbell more directly over the shoulder in latter repetitions as compared to the initial repetitions. ...
Abstract The purpose of this investigation was to examine the effects of cluster set configurations on power clean technique. Ten male, recreational weightlifters performed three sets of six repetitions at 80% of one repetition max with 0 (P0), 20 (P20) or 40 seconds (P40) inter-repetition rest. During the first and second set of P0, the catch and first pull were in a more forward position during repetition 6 as compared to repetition 1, respectively. During the second set of P40, differences in horizontal displacement were found between repetitions 1 and 6 for the second pull and the loop. During the third set of P40, differences in horizontal displacement were found between repetitions 1 and 6 for the first pull, transition, and beginning of the second pull. No differences in horizontal displacement were found between repetitions 1 and 6 during P20. During each set of P0, vertical displacement decreased between repetitions 1 and 6 (1.02 ± 0.07 m vs. 0.94 ± 0.06 m; Mean ± s). Cluster set configurations led to the maintenance of vertical displacement throughout all sets. The results demonstrate cluster set configurations with greater than 20 seconds inter-repetition rest maintain weightlifting technique to a greater extent than a traditional set configuration.
... The mean of the BCF at L5/SI ranged from 3272 to 5877 N and average subject's mass of 67.5 kg, which is comparable as observed in Chen study (24). In this study, subjects significantly increased peak BCF at L5/S1 disc when they had to lift the heavy loads. ...
... In this study, subjects significantly increased peak BCF at L5/S1 disc when they had to lift the heavy loads. This result supports previous studies (24,25), where lifting the heavy loads led to significantly increase peak BCF at L5/S1 disc. Budihardjo et al. in a study conducted to assess the effects of magnitude and knowledge of loads on the L5/S1 compressive force during lifting the loads, showed that during lifting of light load whereas subject no knowledge of weight the load, subjects overestimated the load, and significantly the peak BCF at L5/S1 increased. ...
Background
Low back pain caused by work, ranked the second after cardiovascular diseases, are among the most common reasons of patients’ referral to the physicians in Iran. This study aimed to determine the changes in back compressive force when measuring maximum acceptable weight of lift in Iranian male students.
Methods
This experimental study was conducted in 2015 on 15 young male students were recruited from Tehran University of Medical Science. Each participant performed 18 different lifting tasks involving three lifting frequencies, with three lifting heights, and two box sizes. Each set of experiments was conducted during the 20 min work period using free-style lifting technique. The back compressive force evaluated with hand-calculation back compressive force method. Finally, Pearson correlation test, analysis of variance (ANOVA) and t-test were used for data analysis.
Results
The mean of back compressive force (BCF) for the small and large boxes at a frequency of 1lift/min at heights of F - K height, were 1001.02 (±86.74), 1210.57 (±93.77) Ib, respectively. There was a significant difference between mean BCF in terms of frequencies of lifts (P=0.02). The result revealed significant difference between frequencies of 1 lift/min and 6.67 lift/min (P=0.01). There was a significant difference between mean BCF in terms of the sizes of the two boxes (P=0.001). There was a significant relationship between the BCF and maximum acceptable weight of lift in all test conditions (P=0.001).
Conclusion
BCF is affected by box size, lifting frequency and weight of load.
... Compensatory behaviours with repetitive lifting-induced fatigue have been reported to alter spinal stability and motor control (Bonato et al. 2003;Gregory et al. 2008). Depending on the region of localised muscle fatigue, these adaptations have been seen as altering lifting style, for example switching between stooped and squat postures when lifting (Trafimow et al. 1993; van Dieen et al. 1998;Chen 2000;Bonato et al. 2003). In addition, the higher forward bending acceleration levels with fatigue as reported by Chen (2000) suggest an altered lifting strategy with the development of muscle fatigue. ...
... Depending on the region of localised muscle fatigue, these adaptations have been seen as altering lifting style, for example switching between stooped and squat postures when lifting (Trafimow et al. 1993; van Dieen et al. 1998;Chen 2000;Bonato et al. 2003). In addition, the higher forward bending acceleration levels with fatigue as reported by Chen (2000) suggest an altered lifting strategy with the development of muscle fatigue. ...
This study investigated the effects of task precision demands on behavioral and physiological changes during repetitive asymmetric lifting.
Repetitive lifting encountered in manual material handling leads to muscle fatigue and is a documented risk factor for low back disorder.
A total of 17 healthy volunteers performed repetitive asymmetric lifting for 60 min (10 lifts/min). Task precision demands were imposed by varying the entry width onto the destination conveyor. Physiological changes were assessed using near-infrared spectroscopy obtained from the erector spinae muscles. Three-dimensional spine kinematics and moment responses were quantified to understand behavioral changes during the lifting activity.
Task precision demands showed no effect on erector spinae muscle oxygenation levels. Behavioral changes associated with repetitive lifting included increases in the overall lift duration, peak forward bending motion, and three-dimensional movement velocities of the spine, along with a decrease in the lateral bending moment. Relative to low precision demands, high precision demands resulted in 20% longer placement periods, which, in turn, resulted in a 12% increase in the time-integrated twisting postures and a 10% increase in the time-integrated lateral bending moments during load placement.
The elevated risk of low back injury when lifting under greater precision demands is likely due to the sustained spine twisting and the sustained lateral bending moment on the spine in the final phase of these lifts.
Understanding behavioral changes to repetitive asymmetric lifting, especially for tasks requiring greater precision can be used to support injury prevention efforts.
© 2014, Human Factors and Ergonomics Society.
... Compensatory behaviours with repetitive lifting-induced fatigue have been reported to alter spinal stability and motor control (Bonato et al. 2003;Gregory et al. 2008). Depending on the region of localised muscle fatigue, these adaptations have been seen as altering lifting style, for example switching between stooped and squat postures when lifting (Trafimow et al. 1993; van Dieen et al. 1998;Chen 2000;Bonato et al. 2003). In addition, the higher forward bending acceleration levels with fatigue as reported by Chen (2000) suggest an altered lifting strategy with the development of muscle fatigue. ...
... Depending on the region of localised muscle fatigue, these adaptations have been seen as altering lifting style, for example switching between stooped and squat postures when lifting (Trafimow et al. 1993; van Dieen et al. 1998;Chen 2000;Bonato et al. 2003). In addition, the higher forward bending acceleration levels with fatigue as reported by Chen (2000) suggest an altered lifting strategy with the development of muscle fatigue. ...
This study investigated the effects of a prolonged repetitive asymmetric lifting task on behavioural adaptations during repetitive lifting activity, measures of tissue oxygenation and spine kinematics. Seventeen volunteers repeatedly lifted a box, normalised to 15% of the participant's maximum lifting strength, at the rate of 10 lifts/min for a period of 60 min. The lifts originated in front of the participants at ankle level and terminated on their left side at waist level. Overall, perceived workload increased during the repetitive lifting task. Erector spinae oxygenation levels, assessed using near-infrared spectroscopy, decreased significantly over time. Behavioural changes observed during the repetitive lifting task included increases in the amount of forward bending, the extension velocity and the lateral bending velocity, and a reduced lateral bending moment on the spine. These changes, with the exception of the reduced lateral bending moment, are associated with increased risk of low back disorder.
... The authors assumed that LBP occurs as a result of fatigue failure process, in which microdamage of spinal segments accumulates over repetitive cyclic loading, subsequently leading to overexertion injuries (Gallagher et al. 2007, Gallagher and Heberger 2013, Gallagher and Schall Jr 2017, Zelik et al. 2022, Oomen et al. 2023 Despite such progress in the CSL estimation, the role of muscular fatigue development and the adaptive mechanisms used by workers to counteract muscular fatigue have been overlooked. Alterations in muscular electromyographic (EMG) activities, moving trunk faster, increasing trunk forward flexion angle, holding hand-load closer to the body, and changing kinetic parameters are reported as compensatory behaviors to counteract muscular fatigue during manual handling tasks (Chen 2000, Bernardo et al. 2018). These muscular fatigue-related adaptations affect biomechanical loads on the spine (Boocock et al. 2019), thereby contributing to cumulative damage development. ...
Several methods have been put forward to quantify cumulative loads; however, limited evidence exists as to the subsequent damages and the role of muscular fatigue. The present study assessed whether muscular fatigue could affect cumulative damage imposed on the L5-S1 joint. Trunk muscle electromyographic (EMG) activities and kinematics/kinetics of 18 healthy male individuals were evaluated during a simulated repetitive lifting task. A traditional EMG-assisted model of the lumbar spine was modified to account for the effect of erector spinae fatigue. L5-S1 compressive loads for each lifting cycle were estimated based on varying (i.e., actual), fatigue-modified, and constant Gain factors. The corresponding damages were integrated to calculate the cumulative damage. Moreover, the damage calculated for one lifting cycle was multiplied by the lifting frequency, as the traditional approach. Compressive loads and the damages obtained through the fatigue-modified model were predicted in close agreement with the actual values. Similarly, the difference between actual damages and those driven by the traditional approach was not statistically significant (p = 0.219). However, damages based on a constant Gain factor were significantly greater than those based on the actual (p = 0.012), fatigue-modified (p = 0.017), and traditional (p = 0.007) approaches.Practitioner summary:In this study, we managed to include the effect of muscular fatigue on cumulative lumbar damage calculations. Including the effect of muscular fatigue leads to an accurate estimation of cumulative damages while eliminating computational complexity. However, using the traditional approach also appears to provide acceptable estimates for ergonomic assessments.
... For example, back belts were designed and widely applied in physical demanding tasks to reduce the risks of spine injury. But there is no solid evidence that proves an assistive effects of reducing WMSD or preventing back pain for workers [13,14], and the use of the belts is not considered as an effective ergonomic intervention of LBP by the National Institute of Occupational Safety and Health [15]. ...
This study is to determine how a lightweight active soft waist exoskeleton (ASWE) reduces the oxygen consumption and activity of lower back muscles of the wearer performing the repetitive lifting tasks. The heavy and frequent manual lifting operations are usually associated with an increased risk of injury in the industry. An ASWE is designed to assist workers' spine for lifting weights. The structural composition and operation principle were described for the ASWE. Twelve men were recruited in the experiments as the test subjects. Oxygen consumption and electromyography of the thoracic erector spinae (TES) at the T9 level and lumbar erector spinae (LES) at the L3 level were recorded during 90 lifts in 15 min. Subjects' discomfort and effectiveness evaluation were collected after lifting trials. The average value of oxygen consumption was decreased from form 15.9 ml/kg/min (Without-ASWE condition) to 13.7 ml/kg/min (With-ASWE condition). The increase in electromyography root mean square amplitude from the start until the end of the lifting trial was significantly lower when the ASWE was in use for the TES (162.79 vs. 82.08%) and the LES (122.48 vs. 83.87%). The use of the ASWE showed less oxygen consumption and back muscle contraction compared to the nonuse, which might reduce metabolic consumption or slow down the muscle fatigue level of the wearer's back across the lifting trial. Therefore, wearing the ASWE can reduce the discomfort of body parts, lumbar regions that exercise for a long time.
... Studies have revealed disc compression values between 2.5 and 8.0 kN (Elfeituri and Taboun 2002). Chen (2000) reported peak BCF ( al L5/S1 disc) of 3300 ± 370 N, 4490 ± 520 N and 5050 ± 500 N when lifting a 5-kg, 15-kg and 20-kg loads, respectively, for subjects with an average mass of 67 kg. The mean of the BCF at L5/SI for average subject's mass of 67.5 kg ranged from 3272 to 5877 N (Abadi et al. 2016). ...
Fish dressing is a seasonal activity in seacoast regions. Work related health hazards of women in fish dressing (N = 68) were examined using ergonomic checklist, including fish dressing workplace description, workers description and ergonomic aspects in fish dressing. Working with traditional method of fish dressing, 91.2% women workers suffered from back pain, 85.3% from leg pain, 89.7% from body pain, 83.8% from knee pain and 77.9% from neck pain. Also, 73.5% had skin related problems, 25% had respiratory irritation, 82.3% had a headache and 55.9% had frequent hand injuries. These occupational health hazards were due to the handling of fish material, long hours of sitting work, fixed and awkward work posture, working with arms away from the body, improper fish dressing workplace design etc.
... Even though the human central nervous system can continuously correct the standing balance by making "adjustments" for a better standing balance, an extensive adjustment may cause muscular imbalance (Nagymáté et al. 2018). Furthermore, this imbalance may trigger fatigue (Chen 2000), lowering the muscles' endurance to perform physical activity. ...
Even though pine oleoresin harvesting is labor-intensive forestry work involving manual material handling (especially lifting) and is massively carried out in Indonesia, there is a lack of ergonomics studies on manual pine oleoresin harvesting. This study focused on lifting-related postures in pine oleoresin harvesting. A Three Dimension Static Strength Prediction Program Version 7.1.0 was used to identify the injury risk on the lower back (lumbosacral joint, L5/S1) using biomechanical criteria (compression and shear forces) at extreme postures. Recommended Weight Limit (RWL) and Lifting Index (LI) were calculated for a comprehensive analysis. The exceeding compression and shear forces indicated that the L5/S1 injury risk on oleoresin collecting work (part of oleoresin harvesting) is high. The psychophysical analysis confirmed the findings, as several main postures in this work were categorized as intense manual lifting due to the excessive score of LI. A significant reduction in the L5/S1 compression and shear forces were shown at a simulation using a proposed load threshold (using the calculated RWL).
Keywords: biomechanics, ergonomics, forestry work, manual lifting, oleoresin harvesting
... The dimensional measurement which involved in ergonomics is divided into functional dimensions and anthropometric dimensions. The initial size will depend on the experience of engineers and designers to develop the relevant size of the product [13,14]. With the progress of society and the improvement of living standards, the measurement of human body size is gradually accepted, and corresponding data collection and measurement standards have been established. ...
With the rapidly increase of people’s living standard, more and more people hope to get healthier and longer life. In this study, a kind of rehabilitation fitness machine is designed for disabled people with lower limb, and its daily maintenance work is clearly displayed. The design of the new rehabilitation exercise machine is suitable for disabled people to exercise, which is designed with the theory of ergonomics. Based on ergonomics theory, the design concept of the space, new structure, working space and display device of the six-link mechanism satisfies the conditions of strength and stability.
... In the present study, moment values at L5/S1 ranged from 215.9 ± 9.4 N•m while lifting a 10.3 kg load during the non-constrained condition. Chen (2000) focused on the peak compressive forces at L5/S1 and found that lifting a 10 kg load produced an average value of 3690 ± 41 N for subjects with an average mass of 67 kg. The mean peak compressive forces at L5/S1 for subjects in the current study (average mass: 75 kg) was 3869 ± 528 N while lifting a 10.3 kg load during the non-constrained condition. ...
The purpose of this study was to examine the mechanical stresses on the lower back as the response of different heights of constraining barrier. Ten male subjects lifted a load from the floor to the knuckle height under the non-constrained and the constrained conditions with 4 different heights of constraining barrier (80%, 100%, 120% and 140% of knee height). The constrained condition was defined as the condition where a load was placed on the floor behind a certain level of bar. When lifting of the constrained conditions, subjects significantly increased the peak compressive forces at L5/S1 compared to the non-constrained (3868.8 ± 527.5 N, 4175.0 ± 486.0 N, 4162.4 ± 462.3 N, 4136.0 ± 553.1 N, 4079.4 ± 468.9 N for 0%, 80%, 100%, 120% and 140% barrier height conditions respectively). The subjects moved the load further from L5/S1 in the horizontal direction when lifting during the constrained conditions. While lifting during the constrained conditions subjects generated an increase in the sacral angle and a decrease of the knee flexion. The peak compressive forces at L5/S1 showed a statistically significant quadratic trend. However, the magnitude of the difference of peak compressive forces during the constrained conditions was small.
... Physical fatigue is mainly resulting from three reasons: magnitude of the external load, duration and frequency of the external load, and vibration. It was proved in (Chen, 2000) that the movement strategy in industrial activities involving combined manual handling jobs, such as a lifting job, depends on the fatigue state of muscle, and it is obvious that the change of the movement strategy in the activities directly impacts the motion of the operation and then results in different loads in muscles and joints. If it goes worse, once the desired exertion is over the physical capacity, cumulative fatigue or injury might appear in the tissues as potential risks for musculoskeletal disorders (Ma et al., 2009). ...
Purpose : To analyze spastic dysarthria form in children population dependency of fatigue and faulty posture relationship. Methods: Research performed with the permission of the bioethics committee (RE-BK-063). The Dutch Fatigue Scale (DUFS). Posture in standing was assessed by Hoeger and Kendall. Research subjects n=40. n=20 children diagnosed with spastic dysarthria and n=20 of children without dysarthria. Their age was 10±2.1years. Boys were n=20 and girls - n=20.Results were statistically significant at p
... Factors which have to do with the dynamic change of the body posture also contribute to fatigue accumulation. A study of dynamic lifting revealed that LRs differed significantly when the participant felt fatigue of the upper limbs [7]. So far, it has been difficult to explain the high incidence of musculoskeletal injury, especially tendinitis, as a result of muscle pain and abnormal position of limb or trunk during light repetitive work [8][9][10][11][12]. ...
BACKGROUND: Fatigue is a timely topic that has been studied in a laboratory setting, yet still remains difficult to apply in an industrial setting. OBJECTIVE: The aim of the present study was to define possible indicators of fatigue accumulation for an over shoulder level repetitive lifting work while performing lifting in two different ranges (LR1, LR2) in a supermarket. METHODS: Video-based kinematics parameters were estimated and surface electromyography (EMG) of the anterior deltoid muscle was analyzed for nine healthy female subjects. A static biomechanical model to assess the effect of LRs on fatigue and a new fatigue index to allow for the estimation of substantial fatigue onset time (TSFO) were developed. RESULTS: The data showed that fatigue accumulation strongly depends on the LRs. According to TSFO (time to substantial fatigue onset), shoulder muscle fatigue was unexpectedly lower when performing LR1 than LR2. CONCLUSIONS: The study shows a holistic analysis approach, suitable for the design of work/rest ratios in the occupational ergonomics field.
... Die Autoren um Schipplein folgern daraus, dass die Änderung im Bewegungsverhalten auf der mangelnden Kraftfähigkeit der Knie-Extensoren beruht, unter Ermüdungseinfluss schwere Lasten zu heben. Ähnliche Aussagen werden auch in einem Artikel von Trafimow (Trafimow et al., 1993) (Freivalds et al., 1984;Chen, 2000 ...
Die vorliegende Arbeit untersucht mit elektromyographischen und biomechanischen Methoden lokale muskuläre Ermüdung und die damit verbundenen Veränderungen in der Kinematik und Kinetik eines ausbelastenden Hebetests. Hierzu wurde der PILE-Test (Mayer et al., 1988) verwendet, der als Diagnostikverfahren in der Rehabilitation von Personen mit Rückenbeschwerden eingesetzt wird. In den letzten Jahren sind mathematische Verfahren entwickelt worden, um spektralanalytische Untersuchungen dynamischer Muskelkontraktionen durchführen zu können. In der vorliegenden Arbeit wurde einer dieser Ansätze im Rahmen eines Softwarepakets umgesetzt. Er beruht auf der Verwendung der ''Smooth-Pseudo-Wigner-Ville-Verteilung'', einer biquadratischen Transformation der Cohen-Klasse. Das Verfahren zeichnet sich durch eine hohe Zeit- und Frequenzauflösung aus. Die spektralanalytische Untersuchung von sechs bewegungsrelevanten Muskeln während des Hebetests zeigte für die 22 männlichen Sportstudierenden signifikante Verringerungen der Medianfrequenz lediglich für die Signale der Rumpfstrecker (M. erector spinae, M. gluteus maximus). Dies konnte für die Signale des Kniestreckers (M. vastus lateralis) nicht beobachtet werden. Diese Ergebnisse korrespondieren mit den kinematischen Änderungen im Verlauf der Testdurchführung. Zwischen der Frequenzänderung des M. erector spinae vom Startintervall (geringe Last) zum Schlussintervall (hohe Last) und der Verringerung der Bewegungsamplitude der Rumpfextension wurde eine signifikante Korrelation festgestellt. Aufgrund der daraus ableitbaren Insuffizienz des M. erector spinae kommt es in der Initialphase der Hebung, in der die maximalen Bodenreaktionskräfte auftreten, für nahezu die Hälfte der Probanden zu einem Absenken des Rumpfes. Da dieses Verhalten mit einer erhöhten Belastung im Bereich der lumbalen Wirbelsäule assoziiert wird, sollte die Bewegungsausführung während des PILE-Tests kontrolliert werden, um Gesundheitsrisiken zu vermeiden.
... In compensating for muscle fatigue during a repetitive lifting task, studies have shown that people adapt their working strategy resulting in larger behavioral changes. During repetitive symmetric lifting tasks, behavioral changes have been reported as alternation between stoop and squat postures (31)(32)(33)(34) and between trunk and hip kinematics. (35,36) Behavioral adaptations during a repetitive asymmetric lifting task have been seen as an increase in the amount of forward bending of the spine when initiating lifts and an increase in the lateral bending velocity, (37) both of which are behaviors identified by the Lumbar Motion Monitor model to increase LBD risk. ...
ABSTRACT This study investigated changes in the physiological and behavioral responses to repetitive asymmetric lifting activity after exposure to whole body vibrations. Seventeen healthy volunteers repeatedly lifted a box (15% of lifter's capacity) positioned in front of them at ankle level to a location on their left side at waist level at the rate of 10 lifts/minute for a period of 60 minutes. Prior to lifting, participants were seated on a vibrating platform for 60 minutes; in one of the two sessions the platform did not vibrate. Overall, the physiological responses assessed using near-infrared spectroscopy signals for the erector spinae muscles decreased significantly over time during the seating and the lifting tasks (p < 0.001). During repetitive asymmetric lifting, behavioral changes included increases in peak forward bending motion, twisting moment and three-dimensional movement velocities of the spine. The lateral bending moment of the spine and the duration of each lift decreased significantly over the 60 minutes of repetitive lifting. With exposure to whole body vibration, participants twisted further (p = 0.046) and twisted faster (p = 0.025). These behavioral changes would suggest an increase in back injury risk when repetitive lifting tasks are preceded by whole body vibration exposure.
... Older adults generally have lower muscle strength and load lifting capacities compared with younger adults. Existing literature showed that muscle strength would significantly affect lifting posture and motion patterns (Chen, 2000;Sasaki et al., 2008;Li and Zhang, 2009;Zhang and Buhr, 2002). Therefore, one may expect different biomechanical responses to increasing load weight between younger and older age groups during asymmetric lifting. ...
... À titre d'exemple, lorsque le poids augmente, on observe des changements spon-Manutention : information et décision 205 tanés dans la posture de manutention comme le passage d'une technique genoux fléchis à celle du dos fléchi (Davis, Troup, & Burnard, 1965 ;Schipplein, Trafimow, Andersson, & Andriacchi, 1990). Plus récemment, Chen (2000) a montré l'occurrence d'ajustements spontanés au niveau de l'utilisation de l'accélération lorsque les membres supérieurs accumulent de la fatigue. Les ajustements spontanés correspondent globalement aux possibilités des différents groupes musculaires, comme les quadriceps (Trafimow, Schipplein, Novak, & Andersson, 1993). ...
Definition proposal of handling competency and impacts on training
Handling activities are a source of musculoskeletal injuries–especially on the back–and have been the subject of numerous studies and prevention efforts over the years. Handler training is a common avenue for prevention. The teaching of a movement pattern defined a priori is the foundation of most training programs currently offered in handling. Specifically, training consists of teaching basic guidelines that take shape through standard techniques that handlers should apply at all times. While this approach is appealing in its simplicity and abundantly distributed in workplaces, it is, however, not in line with the actual work of handlers. Some recent studies question the effects of such training, while others bring a fresh perspective to the reality of handling work. Handlers with years of experience use more diverse techniques than what is taught in training. Their challenge is not so much to apply a predefined technique as to adapt it according to the variability of the situations in which they find themselves. Guided by the results of studies on work in real situations, we proposed to update manual handling training. To do this, we defined a general competence, consisting of four dimensions that should guide learning in training: 1) finding the best possible compromise, 2) determining how to organize their work, 3) collecting information to guide the actions, and 4) solving the problems that emerge from the different configurations that can arise in handling situations. Each of these dimensions is reviewed. As a management tool for learning, the concept of action rule is proposed both to get some distance from the action, and to provide support for communication.
... Parkinson and Callaghan (2008) have shown, however, that rest does not significantly increase the resistance of the spine to cumulative compression. Nevertheless, fatigue associated with repetition or cumulative loading is considered a risk factor in itself because it causes muscular contraction (Chow et al., 2004), increases compressive force (Chen, 2000), and leads to lack of coordination. Overall, there is still no clear epidemiological demonstration, as shown by Bedak (2003) in a review of 48 studies in which only six were able to carry out the rather difficult task of documenting workload. ...
... tanés dans la posture de manutention comme le passage d'une technique genoux fléchis à celle du dos fléchi (Davis, Troup, & Burnard, 1965 ;Schipplein, Trafimow, Andersson, & Andriacchi, 1990). Plus récemment, Chen (2000) a montré l'occurrence d'ajustements spontanés au niveau de l'utilisation de l'accélération lorsque les membres supérieurs accumulent de la fatigue. Les ajustements spontanés correspondent globalement aux possibilités des différents groupes musculaires, comme les quadriceps (Trafimow, Schipplein, Novak, & Andersson, 1993). ...
MATERIAL HANDLING : INFORMATION AND DECISION-MAKING
This paper aims to show both how the physical and cognitive dimensions of handling activities are related and how the strategies and handling methods developed make it possible to satisfy the handlers’ objectives. Its findings are based on studies of handling activities that have been conducted over a number of years, both in the field and in a laboratory environment. Handlers were observed, questioned and interviewed and the handling process and incidents were analysed. Expert and novice handlers were studied. Part II briefly presents the general framework. Part III explains the objectives pursued by handlers whilst respecting health, safety and performance. It shows that in order to protect their physical integrity, handlers must develop a modus operandi that enables them to cope with incidents and unforeseen events, whilst at the same time, meeting their goals in terms of job satisfaction. The importance of the information process (passively perceived or actively sought information) is demonstrated in Parts IV and V. The information sought by handlers seek in order to perform handling tasks is first reviewed from the point of view of four basic issues : the characteristics of the handled material (such as weight, mass centre localization, properties), work environment data, the handler’s own capacities, and his performance assessment. The importance of planning and strategies, the information needed to put these strategies in place, and the actual decision-making process are also reviewed. The last part of the paper discusses the practical implications of prevention initiatives.
... À titre d'exemple, lorsque le poids augmente, on observe des changements spon-Manutention : information et décision 205 tanés dans la posture de manutention comme le passage d'une technique genoux fléchis à celle du dos fléchi (Davis, Troup, & Burnard, 1965 ;Schipplein, Trafimow, Andersson, & Andriacchi, 1990). Plus récemment, Chen (2000) a montré l'occurrence d'ajustements spontanés au niveau de l'utilisation de l'accélération lorsque les membres supérieurs accumulent de la fatigue. Les ajustements spontanés correspondent globalement aux possibilités des différents groupes musculaires, comme les quadriceps (Trafimow, Schipplein, Novak, & Andersson, 1993). ...
This paper aims to show both how the physical and cognitive dimensions of handling activities are related and how the strategies and handling methods developed make it possible to satisfy the handlers' objectives. Its findings are based on studies of handling activities that have been conducted over a number of years, both in the field and in a laboratory environment. Handlers were observed, questioned and interviewed and the handling process and incidents were analysed. Expert and novice handlers were studied. Part II briefly presents the general framework. Part III explains the objectives pursued by handlers whilst respecting health, safety and performance. It shows that in order to protect their physical integrity, handlers must develop a modus operandi that enables them to cope with incidents and unforeseen events, whilst at the same time, meeting theft goals in terms of job satisfaction. The importance of the information process (passively perceived or actively sought information) is demonstrated in Parts IV and V. The information sought by handlers seek in order to perform handling tasks is first reviewed from the point of view of four basic issues: the characteristics of the handled material (such as weight, mass centre localization, properties), work environment data, the handler's own capacities, and his performance assessment. The importance of planning and strategies, the information needed to put these strategies in place, and the actual decision-making process are also reviewed. The last part of the paper discusses the practical implications of prevention initiatives.
... Nielsen et al., (1998) evaluated the muscular load on the low back in different lifting conditions and they reported that the maximum muscular load occurred at the low lifting height (36.3 and 54.4 cm) whereas the maximum muscular load on the shoulders occurred at the high lifting height (144.9 and 163.0 cm), a trade-off in position occurred while lifting in different frequencies. Later, Chen (2000) showed that the lifting strategies changed as a function of arm fatigue, resulting in increased lower back loading. Arm fatigue resulted in increased compressive forces at the L5/S1 disc due to the use of accelerated techniques and the inherent disadvantage of these techniques in the pre-lifting posture. ...
The National Institute for Occupational Safety and Health (NIOSH) developed a lifting equation in 1981 to indicate “safe” occupational lifting limits. This equation was revised in 1991. The equation uses a series of lifting multipliers (parameters) to calculate corresponding recommended task weight limits. Due to the nature of risk factor interactions, the limits obtained from the NIOSH equation may not be appropriate for all lifting tasks. This laboratory experiment examined the effect of lifting parameters and their interactions as follows: lifting frequency, vertical lifting distance, and load weight. In this simulation study, 10 female building construction workers lifted weights in 48 different combinations of lifting parameters, in which four different lifting frequencies (1, 4, 7, and 14 lifts min−1), three different load weights (5, 10, and 15 kg) and four different vertical lifting heights (knee, waist, shoulder, and maximum reach) were considered. The subjects did symmetric lifting for 10 min period in sagittal plane adopting free-style lifting technique. The recorded working heart rates were normalized based on the maximum heart rate obtained during maximum aerobic power measurement. MANOVA result showed that the main effects were significantly (p<0.0001) related with normalized working heart rate and the interaction effects of different lifting parameters contributed 10.01% of total variance of normalized working heart rate. Factorial design was applied to verify the interaction effects. Then, stepwise linear regression analysis was performed to identify the best predictive model using important parameters. It was observed that the contribution of interaction factors were not in similar pattern in case of different frequency responses. Finally, it is concluded that the interaction effects between different lifting parameters must be considered in addition to the effects of individual lifting parameters for further research as it implicates potential modifications to the currently recommended weight load estimation procedure.
... However, the change of the physical status can be experienced everyday by everyone, and different working procedures generate different fatigue effects. Furthermore, it has been reported that the motion strategy depends on the physical status, and different strategies were taken under fatigue and non-fatigue conditions (Chen, 2000; Fuller et al, 2008). Therefore, it is necessary to create a virtual human model with a variable physical status for the simulation. ...
Virtual human techniques have been used a lot in industrial design in order to consider human factors and ergonomics as early as possible. The physical status (the physical capacity of virtual human) has been mostly treated as invariable in the current available human simulation tools, while indeed the physical capacity varies along time in an operation and the change of the physical capacity depends on the history of the work as well. Virtual Human Status is proposed in this paper in order to assess the difficulty of manual handling operations, especially from the physical perspective. The decrease of the physical capacity before and after an operation is used as an index to indicate the work difficulty. The reduction of physical strength is simulated in a theoretical approach on the basis of a fatigue model in which fatigue resistances of different muscle groups were regressed from 24 existing maximum endurance time (MET) models. A framework based on digital human modeling technique is established to realize the comparison of physical status. An assembly case in airplane assembly is simulated and analyzed under the framework. The endurance time and the decrease of the joint moment strengths are simulated. The experimental result in simulated operations under laboratory conditions confirms the feasibility of the theoretical approach.
... Physical fatigue is mainly resulting from three reasons: magnitude of the external load, duration and frequency of the external load, and vibration. It was proved in (Chen, 2000) that the movement strategy in industrial activities involving combined manual handling jobs, such as a lifting job, depends on the fatigue state of muscle, and it is obvious that the change of the movement strategy in the activities directly impacts the motion of the operation and then results in different loads in muscles and joints. If it goes worse, once the desired exertion is over the physical capacity, cumulative fatigue or injury might appear in the tissues as potential risks for MSDs. ...
Automation technique has been widely used in manufacturing industry, but there are still manual handling operations required in assembly and maintenance work in industry. Inappropriate posture and physical fatigue might result in musculoskeletal disorders (MSDs) in such physical jobs. In ergonomics and occupational biomechanics, virtual human modelling techniques have been employed to design and optimize the manual operations in design stage so as to avoid or decrease potential MSD risks. In these methods, physical fatigue is only considered as minimizing the muscle or joint stress, and the fatigue effect along time for the posture is not considered enough. In this study, based on the existing methods and multiple objective optimisation method (MOO), a new posture prediction and analysis method is proposed for predicting the optimal posture and evaluating the physical fatigue in the manual handling operation. The posture prediction and analysis problem is mathematically described and a special application case is demonstrated for analyzing a drilling assembly operation in European Aeronautic Defence & Space Company (EADS) in this paper.
... Schipplein et al. (1990) suggested that the quadriceps muscle strength limits the ability to lift with flexed knees. When muscles became fatigued, the tendency of replacing a leg-lift strategy with a back-lift strategy was observed (Puniello et al., 2001; Sparto, Parnianpour, Reinsel, & Simon, 1997; Trafimow, Schipplein, Novak, & Andersson, 1993; Zhang & Buhr, 2002), and lifting dynamics altered significantly as well (Chen, 2000). Fogleman and Smith (1995) investigated changes in lifting patterns made by the participants practicing during a prolonged period of time, and their investigation indicated a change from a leg lift to a back lift. ...
This study investigated whether relative strength between the back and knees can differentiate and predict lifting strategy and the effects of gender, load magnitude, and knowledge of strength on the strategy.
Although muscular strength is thought to play a vital role in the mechanics of lifting, how localized joint strengths and their relations influence lifting strategy remains unclear.
Thirty-two participants (16 men and 16 women) underwent isokinetic strength tests and were then divided into two groups: one provided with the knowledge of their strength test results and the other not. They subsequently performed the same set of simulated lifting tasks while their lifting kinematics were being recorded. Postural indices to quantify the lifting strategies were derived from the kinematic data.
The ratio of back strength versus total knee strength and gender had significant effects on measures quantifying the lifting strategy. A statistical model incorporating gender, strength, and anthropometry achieved an R2 value of .64 and predicted correctly 76% of lifting strategies used by individual participants.
Individuals with back strength greater than their total knee strength tended to use a back-preferred lift strategy, and vice versa, suggesting that muscular strength is a determining factor of lifting strategy. Application: An emphasis on additional knee strengthening in a training program may change the tendency of using and overstressing the back. Application of modeling and simulation technology for ergonomics design can be enhanced by more individually and accurately specified lifting strategies based on anthropometry and strength profiles.
... Low back pain(LBP) is a prevalent problem which causes human suffering and cost for workers and their employers . 60~80% of the adult population have experiences of LBP at least once in their lifetimes12345. Despite improved working conditions, including progress due to automation , many objects in the industry are still handled manually . ...
In this study, kinematics and kinetics of the lower extremity joint and the lumbar lordosis during two different symmetrical lifting techniques(squat and stoop) were examined using the three-dimensional motion analysis.
Twenty-six young male volunteers were selected for the subjects in this study. While they lifted boxes weighing 5, 10 and 15 kg by both squat and stoop lifting techniques, their motions were captured and analyzed using the 3D motion analysis system which was synchronized with two forceplates and the electromyographic system. Joint kinematics was determined by the forty-three reflective markers which were attached on the anatomical locations based on the VICON Plug-in-Gait marker placement protocol. Joint kinetics was analyzed by using the inverse dynamics. Paired t-test and Kruskal-Wallis test was used to compare the differences of variables between two techniques, and among three different weights. Correlation coefficient was calculated to explain the role of lower limb joint motion in relation to the lumbar lordosis.
There were not significant differences in maximum lumbar joint moments between two techniques. The hip and ankle contributed the most part of the support moment during squat lifting, and the knee flexion moment played an important role in stoop lifting. The hip, ankle and lumbar joints generated power and only the knee joint absorbed power in the squat lifting. The knee and ankle joints absorbed power, the hip and lumbar joints generated power in the stoop lifting. The bi-articular antagonist muscles' co-contraction around the knee joint during the squat lifting and the eccentric co-contraction of the gastrocnemius and the biceps femoris were found important for maintaining the straight leg during the stoop lifting. At the time of lordotic curvature appearance in the squat lifting, there were significant correlations in all three lower extremity joint moments with the lumbar joint. Differently, only the hip moment had significant correlation with the lumbar joint in the stoop lifting.
In conclusion, the knee extension which is prominent kinematics during the squat lifting was produced by the contributions of the kinetic factors from the hip and ankle joints(extensor moment and power generation) and the lumbar extension which is prominent kinematics during the stoop lifting could be produced by the contributions of the knee joint kinetic factors(flexor moment, power absorption, bi-articular muscle function).
This paper proposes a three-layer elastic cloth fabric mechanism for an assistive suit with adjustable structure (based on a two-layer non-adjustable structure) to achieve different assistive force profiles. This increases the assistive force on the lower-back muscle group and alleviates the undesired pre-tension that acts on a user when the rubber belt located on the back is pulled to provide a higher assistive force. With the lower pre-tension, users would not encounter body fatigue as rapidly as in the past. The adjustable feature enables the structure to provide a force that increases gradually to a high level over a short distance without pre-tension. An experiment involving the measurement of muscle activities is conducted to evaluate the variation in assistive force in the lower back by comparing the three-layer suit to the two-layer non-adjustable suit. The experimental results show that the new three-layer structure successfully assists without pre-tension in the lower-back muscle group similar to the two-layer structure with pre-tension. A simple questionnaire is also administered to collect feedback from participants on the differences between the three-layer suit and two-layer suit in terms of wearing perception. Over half of the participants reported that the perception of pre-tension in the three-layer suit is lower than that in the two-layer suit.
Lifting at work is considered an important risk factor for low back pain (LBP). It results in considerable human suffering and economic burden on the industry. The present study attempts to throw light on a few lifting parameters and their effect on a manual lifting task. Experimental investigations were carried out to examine the effect of container and worker characteristics on maximum acceptable load limit (MAWL), oxygen uptake and compressive forces developed in the L5/S1 joint during the task. A psychophysical approach was used. ANOVA was carried out on the data collected. The results indicated that box dimensions, handle position, age and experience had a statistically significant effect on MAWL. Further, it was found that despite higher MAWL, experienced subjects showed a lower oxygen uptake as compared to novice ones across all age groups. The L5/S1 compressive force was, however, higher for experienced subjects.
Workers engaged in repetitive manual material handling (MMH) generally suffer from work-related musculoskeletal disorders (WMSDs), particularly in the arms, shoulders, neck, and waist; this significantly limits the individual's strength and ability to work. Currently, research on upper-limb injuries affecting manufacturing workers focusses on the effect of different working conditions on specific muscle fatigue. However, research on the fatigue transformation relationship among various muscles in the process of working is lacking. Therefore, the purpose of this study was to investigate the fatigue changes between the upper-limb muscles during rotary handing. In this study, 13 male subjects were studied to simulate rotating handling during the manual handling process using surface electromyography (sEMG). Handling angles of 90°, 45°, and 0° were arranged as single variables to conduct the single-factor experiment. The sEMG of the brachioradialis, biceps brachii, trapezius, and multifidus muscle was measured during the operation. The results of this study indicate that the characteristics of muscle fatigue are different at different rotation angles: the multifidus muscle and trapezius were fatigued when the rotation was 90°. Under the condition of a 45° rotation, the activities of the four muscles fluctuated significantly. The slope of the median frequency of the muscles was positive, the load of the four muscles was evenly distributed, and no local fatigue was observed. Under the condition of a 0° rotation, the sEMG indicated that the brachioradialis muscle was fatigued, while the other three muscles had lower loads.
This paper proposes a close-fitting assistive suit, called e.z.UP ® , with a passive actuation mechanism composed of an adjustable structure. The suit can adequately assist the back and arm muscles of a user with the proposed layout of an arm assistive belt and a two-layer structure, respectively. With its lightweight characteristic (i.e., weighing 0.75 kg only), the proposed suit is portable and easy to wear without additional burden. By using the averaged Japanese body data, a simulation was conducted based on a human body model wearing our proposed suit to evaluate the layout of the arm assistive belt. The simulation results prove that the proposed suit can adequately assist the user’s arm muscles based on the user’s motion. An experiment involving the measurement of muscle activities is also implemented with seven young subjects and seven middle-aged subjects to evaluate the arm assistive belt and the two-layer structure. The experimental results reveal that the proposed suit can successfully and appropriately assist both the arm and back muscles simultaneously.
-Ergonomic risk factors are vital for posture prediction of human, working in manual assembly is founded on the human movements at each joint to decrease energy level and fatigue level of the worker. In this study a simple measure of human performance is introduced that permits the mathematical model to assess the cost functions. Here human is modeled as a structure of 20 DOF. The necessary procedure is the evaluation of the performance in the system of cost factors. Here two main cost factors are considered as discomfort factor and energy expenditure rate in different limbs movement. The basic objective is to optimize the limb movements to the cost factors. The above procedure is verified through a example case of fly ash bricks plant. Here two workers are stacking bricks in stacking pan. A Multi Objective Optimization (MOO) technique is utilized for the prediction of posture, in which cost factors are minimalized, ultimately reduced level of ergonomic risk factor.
Introduction: Conventional wisdom to avoid back pain while making your bed recommends not to lean across your bed to tuck in the sheets, and to keep your back straight and use Core Muscles. This is not practical or possible with any of the many different designs currently available. At present, there is no safe way to make your bed, which can significantly increase the risk of injury and create lifelong disabilities for both individuals and certain professional bedmakers such as house keepers, and caregivers. Objective: It was hypothesized that the use of an Instant Tuck™ Mat can significantly lower the Back-Compression Force (BCF) on the Lower Back and fall far below the risk threshold level stated by the NIOSH. The Instant Tuck™ Mat addresses this major health problem of back pain and injuries by eliminating the need to ever lift a mattress when making the bed. Method: A sample of 35 subjects performed the task of making a bed with a queen-sized mattress with and without the Instant Tuck™ Mat in a random order. BCF, the number of lifts to make the bed as well as the length of time for each lift, and the number of times each individual bent forward was measured during each trial. Results: There were significant differences for all the measured variables. Regarding the BCF, there was an approximately 85% reduction of pressure on the lower back when using the Instant Tuck™ Mat vs. not using it, which was a highly significant decrease (p<.001). Also, the number of times the mattress was lifted was lower by 12 times when using the Instant Tuck™ Mat vs. not using it (p<.001). Finally, the times each individual bent down was approximately 9 times less when using the Instant Tuck™ Mat vs. not using it (p<.001). Conclusion: BCF’s making a bed in its current form is by a wide margin out of compliance with NIOSH standards and as a result it poses a significant risk of injury especially for those who are required to perform this for their occupation, such as hotel housekeepers and hospital, nursing home, and in-home caregivers. Making a bed using the Instant Tuck™ Mat reduced the BCF’s by 85% and is in line with NIOSH standards. The Instant Tuck™ Mat has that it can make the repetitive act of making a bed safe and that it can significantly reduce the risk of injury based on NIOSH standards.
The muscle injuries of manual handling workers, caused by the repeated motion and heavy load in the daily tasks, strongly influence their quality of life. To prevent muscle injuries in many occupations, a close-fitting assistive suit weighing 0.75 [kg] with the passive actuation mechanism and adjustable structures is proposed to assist not only the back muscle but the arm muscle of manual handling workers according to the user intention. An experiment with electromyography for measuring the muscle activities is conducted with six subjects to practically confirm the effectiveness of the suit. The experimental results revealed and proved that the proposed suit can successfully and appropriately assist not only the arm but also the back muscle with a lifting-up motion, simultaneously.
Background:
A wearable power assist device was developed to reduce the stress on the lower back by using pneumatic muscles. The purpose of this study was to explore whether the assist device could reduce the activity or fatigue of lower back muscles during a repetitive lifting task.
Methods:
Twelve male subjects participated in the study. Electromyography of the thoracic erector spinae at the T9 level and lumbar erector spinae at the L3 level was recorded during 90 lifts in 15 min. Subjects' heart rate and Borg's Rate of Perceived Exertion Scale score were recorded during lifting sessions.
Findings:
The electromyography amplitude of thoracic erector spinae and lumbar erector spinae was only increased by 32.45% and 40.17%, respectively, when the wearable power assist device was used when comparing the pre- and post-lifting task. Whereas it was increased by 125.78% and 85.90%, respectively, when the wearable power assist device was not used. The decrease in electromyography median frequency from the start until the end of the lifting session was significantly lower when wearing the assist device for the thoracic erector spinae (2.72% vs 7.45%) and the lumbar erector spinae (3.91% vs 13.70%). Use of the assist device also significantly reduced the percentage change in heart rate and Borg Scale (p < 0.05).
Interpretation:
The use of the wearable power assist device showed less back muscle contraction compared to the no-use, which can potentially minimize the level of back muscle fatigue across the lifting session.
The inverse kinematic analysis is required in many technical applications. Due to the non linearity of the system, resolving the Inverse Kinematics (IK) for robotic system becomes more challenging problem. In this chapter, the problem of IK for medical application is faced, based on human lower limb as being the three arm robotic system depending on the physiological constaints. A system analysis is carried out specially in three dimensionnel space. The developed forward kinematic model leads to define the feasible workspace of the human leg in the considered configuration. A constructive algorithm to compute the optimal IK of robot system is outlined, based on human performance measure that incorporates a new objective function of musculoskeletal discomfort. The effectiveness of the proposed approach is tested, and the algorithmic complexity is finally discussed.
The aim of this chapter is to presents a Kinematic analysis of a Cable-Driven Robot for rehabilitation use of human lower limb, by taking into account the constraints required by the entrainment system and the mobile platform (human leg). The proposed approach is focused on optimizing the manipulability and the human performance of the human leg, as being a physiologically constrained three-link arm. The obtained forward kinematic model leads to define the feasible workspace of the human leg in the considered configuration. Using an effective optimization-based human performance measure that incorporates a new objective function of musculoskeletal discomfort, and the mapping relation between articular joints actuator, length cables and articular joint mobile platform, the optimal inverse kinematic (IK) model is obtained.
Background:
The Functional Capacity Evaluation (FCE) is a tool used in the return-to-work process to guide treatment and decision making. Individual abilities and maximum capacity can be determined through visual observations of changes in mechanics as intensity increases.
Objective:
The purpose of this study was to determine kinematic differences between sexes and intensity levels of two common FCE tasks to establish normative behaviours.
Methods:
Upper limb and torso kinematics were collected from 30 participants as they performed the overhead lift and overhead work FCE tasks. Mean, maximum, and minimum values were calculated for clinically relevant joint angles. Mean and maximum segment velocity was also calculated and each variable was tested with a mixed model ANOVA.
Results:
During the overhead lift task, maximum torso flexion and maximum torso extension increased from the lightest to the heaviest load. Humeral flexion angle at the beginning of the lift and wrist ulnar deviation also increased with load. Torso extension, humeral flexion and axial rotation, and wrist extension all increased with time during the overhead work task.
Conclusions:
Increasing intensity during the overhead tasks influenced kinematic variables. These observable changes can be used by evaluators to more reliably determine safe maximum capacities for each patient and identify compensatory actions.
Lifting is a common activity to below-knee amputees (BKA) in occupational and living occasions. Appropriate lifting posture is crucial to physical safety and health to those BKAs. Often healthy parts of BKAs might be hurt due to extra and asymmetric force exertion compensating for deficiency of disabled body parts. To prevent further hurt, a validated biomechanical model describing lifting is essential to analyze lifting behavior of those handicapped. In this study, twelve BKAs were recruited to lift 45 N weights from the floor. Subjects are asked to lift three levels of weights (0 N, 30 N, 60 N) by two postures: squat lifting and stoop lifting. Twelve non-BKAs were recruited as comparison group to study the variance caused by disability. Calculated forces based on Anybody were compared with EMG signals of body parts on spine and thigh. A framework of three-level constraints models were applied to adjust the difference between calculated forces and EMGs and the results validate the model.
In thís study, lower extremíty jo찌t kinematics and kinetícs and lumbar lordosis were investigated for two different symmetrícal lifting techniques(squat and stoop) using the three-dimensíonal motíon ana/ysis. Twenty-six male volunteers lífted boxes weighing 5, 10 and '15kg by both squat and stoop líftíng techniques' There were not sígnífícaηt dífferences ín maxímum lumbar joiηt moments between the two techniques. The hψ and ankle contríbuted the most part of the support moment duríng squat lí엄íng， and the knee flexion moment played an ímportant role in stoop lifting. The híp, ankle and lumbar joints generated power and only the knee joint absorbed power in the squat liftíng. The knee and ankle joínts absorbed power, the híp and lumbar joints generated power ín the stoop lìfting. The bi-articular antagoníst musc/es' co-contractíon around the knee joínt duríng the squat lifting and the eccentric co-contractíon of the gastrocnemíus and semítendínosus were found to be ímportant for straightening up duríng the stoop lífting. At the time of lordotic curvature appearance ín the squat lifting, there were significant correlatíons ín al/ three lower extremity joint moments with the lumbar joint. Differently, only the hip moment had sígnífícant correlation with the lumbar joínt ín the stoop lífting. In conclus;， α7， the knee extension which ís prominent kinematics duríng the squat lifting was produced by the contríbutions of the kinetic factors from the hψ and ankle joints(extensor moment and power generation) and the lumbar extension which is prominent kínematics duríng the stoop lífting could be produced by the contributíons of the knee joint kinetic factors(flexor moment, power absorption, bi-ar1icular muscle function) Key Words: lifting (들기)， Squat lifting (쪼그려 틀 7)) ， Sioop lifting (허러굽혀 들기)' Low Back Pain Support Moment (지 지 .2엔 g:), Joínt Power (판설 잃 헬)' Lumbar Lordosis Joint Moment 만) 요통은 산업현장에서 많은 사회적 비용을 지 불하게 하는 유병률이 높은 산업재해 질환 중 하 나이며 성인인구의 80% 이상이 일생 통안 적어도 한 변은 경험하는 질환이다 미국성인의 5%에 달 하는 인구가 매년 요통을 경험하며 미국 직장인 남녀의 연간 요통 유병률이 각각 44%， 48.2%에 달
The purpose of this study was to determine if an on-body personal lift assistive device (PLAD)1 affected oxygen consumption during a continuous lifting task and to investigate if any effect could be explained by differences in muscle activity or lifting technique. The PLAD, worn like a back-pack, contains a spring-cable mechanism that assists the back musculature during lifting, lowering, and forward bending tasks. Males (n = 15) lifted and lowered a box loaded to 10% of their maximum back strength at 6 times/minute for 15-minutes using a free-style technique under two conditions: wearing and not wearing the PLAD. Oxygen consumption was collected continuously for the first condition; then the participants rested until their heart rates returned to resting levels before repeating the protocol for the second condition. Knee flexion was monitored using Liberty sensors at the hip, knee, and ankle. EMG of the thoracic and lumbar erector spinae (TES, LES), biceps femoris, rectus femoris and gluteus maximus were gathered using a Bortec AMT-8 channel system. VO2 measures were averaged across the duration (15 min) for each condition. Results showed no differences between oxygen consumption during the PLAD and no PLAD conditions. When wearing the PLAD, the TES demonstrated an 8.4% EMG reduction when lowering the box while the biceps femoris showed a 14% reduction while lifting the box. Knee angles, used as a proxy for stoop or squat lifts, were highly variable for both conditions. In conclusion, the PLAD had no effect on oxygen consumption and, therefore, neither workers nor employers should increase the tasks demands when wearing this ergonomic aid.
Relevance to industry
While the PLAD reduced musculoskeletal effort required by back musculature, loads or rates of lifting should not be increased since there is no change in the overall physical demand of the task.
Fatigue is an important failure mode for swing frame of mine trunk. However, swing frame have so many attributes that it is difficult to analyze their fatigue damage using experimental measurement methods. In this paper the stress and strain analysis of swing frame is obtained by MSC.Patran software with the help of the dynamic analysis from MSC.Adams software. Improved model of swing frame is made according to stress concentration. The fatigue life predictions of unimproved and improved swing frame are achieved via the theory of cumulative damage in fatigue by MSC.Fatigue software. The results show that the fatigue life of improved swing frame is extended and satisfied with the practical application.
In this study, we analyzed joint moments during the symmetrical lifting in two different postures, using the three-dimensional motion analysis. Boxes weighing 5, 10 and 15kg were lifted by both squat and stoop techniques. The ankle moment in stoop was always larger than that in squat and the support moment was the largest at the end of the lifting in both techniques. The knee flexion moment played an important role in stoop lifting to support the lower limbs. In the end stage of the lifting, the hip joint showed less contributions on the support moment in both lifting techniques. However, the maximum hip extension moment in stoop lifting was larger than that in squat. In addition, the maximum waist moment in squat was larger than in stoop. Therefore, these results could support the previous research that the squat lifting was not the best strategy with no harm to the waist. It is expected that these results could provide a basic information to analyze and propose an efficient lifting strategy.
In this study, joint moments, support moments and lumbar lordosis were investigated for two different symmetrical lifting techniques using the three-dimensional motion analysis: squat and stoop. Thirteen male volunteers lifted boxes weighing 5, 10 and 15kg by both squat and stoop lifting techniques. There were no significant differences in maximum lumbar joint moments between two techniques. And the extension moments of hip and ankle joints contributed the most to support the body in squat lifting, and the knee flexion moment played an important role in stoop lifting. There were individual differences in lower extremity joint moments when the lumbar lordotic curve appeared. However, the correlations about angles and moments between lumbar and lower extremity joints could confirm the results from the support moment analysis. In conclusion, lower limbs contribute to minimize mechanical stress on the waist by the change of lordotic curvature in the lumbar spine for the safe lifting technique.
Musculoskeletal pain and injury continue to be prevalent sources of disability for thousands of workers in the U.S. every year. Proactive approaches to the reduction of this incidence attempt to prevent the injury by effecting task design so that human capabilities and limitations are driving factors in the task design and analysis process. Knowledge about the posture and kinematics that might be employed by an individual in performing a task is an important element of these proactive approaches to task design and analysis, especially for manual materials handling (i.e., lifting) exertions. In turn, accurate models that predict posture and kinematics can reduce the need for empirical postural and kinematic data in this task development process. Artificial neural networks were used in this investigation to achieve these predictions. As input, these networks received information about lift characteristics (e.g. target location, movement duration) and returned a predicted set of joint angles. Two types of networks were created, one to predict static posture based on target position, the second to predict the time histories of several joint angles (i.e., kinematics) as an object is lifted or lowered. Initial networks were created for sagittally symmetric lifts (two dimensions), but the final set of networks was expanded to make predictions for symmetric and asymmetric lifts in three dimensions. Networks were trained and verified with an empirical set of non-cyclic lifting motions. Notably, the within-subject variability in these motions was similar in magnitude to the associated between-subjects variability. In general, the networks were able to assimilate the data relatively well, especially in predicting kinematics, where root mean square errors were typically smaller than 20 degrees. These errors were similar in magnitude to the levels of within-subject variability observed in the dataset. Network performance also compared favorably to other existing models, typically resulting in smaller prediction errors than these other approaches. System requirements: PC, World Wide Web browser, and PDF reader. Available electronically via the Internet. Title from electronic submission form. Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 2005. Vita. Abstract. Includes bibliographical references.
A review of the biomechanics of weight lifting as it relates to low-back stresses is presented first. This serves as the basis for the development of a Lifting Strength Rating (LSR) methodology. Then a study is reported wherein the LSR methodology is used to evaluate 103 jobs having various amounts of required two-handed load lifting. The 411 people populating these jobs were also evaluated. For a period of one year following their evaluation, any low-back pain problems in the group were noted. The primary result of the field study is that the incidence rate of low-back pain is correlated with higher lifting strength requirements as determined by assessment of both the location and magnitude of the load lifted. It is, therefore, recommended that load lifting be considered potentially hazardous, and that the LSR methodology be used to guide corrective actions.
OBJECTIVE: The purpose of this study was to develop a non-invasive method to predict the lumbosacral and vertebral angles. DESIGN: The candidate predicting variables were the externally measured marker angle, pelvic angle, and lumbosacral angle. BACKGROUND: Several investigators used surface rigid markers to represent the angles of lumbosacral vertebrae. Previous studies show a high level of validity for measuring the lumbar curvature during stance and for obtaining the vertebral angle in the lumbar region. However, our review of literature failed to find a data transformation model illustrating the lumbosacral vertebral angle using external measurements as predictors. METHODS: Sixteen healthy male subjects participated in the radiographic and videographic measurements. Data of 12 of the 16 subjects were used for model development, and data of the other four subjects were used for model validation. RESULTS: The results showed significant differences between the directly measured vertebral angle from the X-ray film and the externally measured angles of the surface markers at the L(5) and S(1) levels (P<0.05). Linear regression models for calculating vertebral angles were developed with R(2) values of 0.97, 0.98, 0.91, and 0.92 for the vertebral levels of L(1), L(3), L(5), and S(1) respectively. The validation result showed that there was no significant difference between the calculated and the X-ray data. CONCLUSIONS: The protocol of using the skin-surface rigid markers and the predicting models was justified in the study to provide a simple and valid non-invasive method for the recording of the internal vertebral angle in the sagittal plane. RELEVANCE: Measurements of lumbosacral vertebral angle are important in assessing the stresses acting on the low back in lifting. The results of this study provided a simple and valid non-invasive method by rigid markers for the prediction of internal vertebral angles under various trunk positions.
Little information is available in the literature on postures adopted for forceful tasks, particularly in industrial jobs such as maintenance where operators may be working in awkward or confined spaces. The present study was undertaken to show the effects of work location and reach distance on posture, and to identify factors which determine the choise of posture. The results have shown that the posture of the arm and shoulder is critical in the transmission of high forces, and involves the use of various postural strategies to maintain the stability of the joints of the arm.
Sagittal and coronal moment arm lengths of spinal extensors, flexors, and rotators were measured from the cross-sectional CT scans of 56 patients (35 males and 21 females) with no musculoskeletal disorders at 7th and 12th thoracic vertebral levels and 3rd and 5th lumbar vertebral levels. The sample had a mean age of 58·6 years (s.d. 15·5 years, range 23-90 years), mean body weight 73·15 kg (s.d. 13·9 kg, range 49·5-11·28 kg) and a mean body height of 169·9cm (s.d. 11·9cm, range 130-189cm). Transverso spinalis (TS), erectores spinae (ES), quadratus lumborum (QL), psoas (PS), rectus abdominis (RA), internal obliques (10), and external obliques (EO) were measured at L3 and L5 levels. TS, ES, RA and combined obliques (CO) were measured at the T12 level; however, at T7 level only TS and ES were measured. The extensor moment arm measured (6·0cm) was significantly different from the conventional value (5·0 cm). The moment arms of these muscles on the right and left sides did not differ significantly. The effect of age on the moment arm was significant only with respect to people over 60 years on the coronal plane measurements of the obliques. The gender significantly influenced the moment arms. The height, weight, and height-weight product did not regress significantly on moment arms.
This study has attempted to document how general motion alterations could change the loading on the lumbar spine during asymmetrical manual materials handling. Two general motion principles were explored: stability (modification of the width of the base of support) and fragmentation (insertion of a pause). It was hypothesized that during asymmetrical materials handling (1) a decrease in the width of the base of support may increase lumbar spine loading and (2) the insertion of a pause may reduce lumbar spine loading. Four male subjects performed asymmetrical tasks involving the reception and lifting of an 11.6 kg box. The magnitude of lumbar spine loading was estimated by computing 3D components of the net muscular moment, articular force and their respective loading rate at the L5/S1 joint. Comparisons were made between a wide and a narrow base of support task (stability) and between a continuous and a paused task (fragmentation). The results showed no difference for either moment, force or their loading rate between the experimental conditions, except for one component of the net moment in the fragmentation comparison. More research is needed to clarify the application of these two principles in asymmetrical materials handling.
The main objective of this study was to investigate different limiting factors in psychophysically determined maximum acceptable weight of lift (MAWL) for frequent and infrequent tasks. Seven isometric strengths were tested to obtain various muscular strength scores. They were: back lift (BL), leg lift (LL), and pulling backward strength (PB), arm lift (AL), shoulder lift (SL), and vertical pulling up strength (PU). Capacity-predicting models were developed based on the best single strength and anthropometric variables in task conditions of 3 lifting frequencies, 2 lifting ranges, and 2 sizes. To realize the effect of task conditions on strength recruitment, the lifting posture was recorded and the EMG activities of arm (biceps brachii), back (erector spinae), and leg (rectus femoris) of each strength test were also recorded. It was found that different strength-limiting factors do exist between the MAWL of frequent and infrequent lifting tasks. The conclusion was supported by the fact that different strength variables of PB and PU were selected as the best single predictor of the one time maximum MAWL and the MAWL of 4 lifts/min. Posture analysis indicated that more flexed elbow and shoulder joints were observed in the infrequent lifts. The advantage of the stiffened upper extremity is that it can shorten the moment of arms, particularly when the loads are heavy. IEMG data indicated that besides back strength, various muscle strengths (arm, back, and leg) do contribute differently in various lifting phases.
Sumario: This paper summarizes the variables affecting the ability to handle materials and the three basic approaches to determining capacities and limits for MMH: the biomechanical, the physiological, and the psychophysical approaches. The paper presents the various models develop in each of these approaches, together with a discussion of progress made and difficulties encountered in deriving capacity recommendations from each. Finally, the paper presents the latest recommendation on how these approaches can be integrated into a single comprehensive model for establishing lifting limits
A biomechanical evaluation of the job-related stresses imposed upon a worker is a potential means of reducing the high incidence rates of manual material handling injuries in industry. A biomechanical model consisting of seven rigid links joined at six articulations has been developed for this purpose. Using data from cinematographic analysis of lifting motions the model calculates: (1) body position from articulation angles, (2) angular velocities and acceleration, (3) inertial moments and forces, and (4) reactive moments and forces at each articulation, including the L5/S1 joint.Results indicated effects of the common task variables. Larger load and box sizes increased the rise times and peak values of both vertical ground reaction forces and predicted L5/S1 compressive forces. However, boxes with handles resulted in higher L5/S1 compressive forces than for boxes without handles. Also, in lifting the larger boxes the subjects did not sufficiently compensate with reduced box weights in order to maintain uniform L5/S1 compressive forces. Smoothed and rectified EMG of erector spinae muscles correlated significantly with L5/S1 compressive forces, while predicted and measured vertical ground reaction forces also correlated significantly, indicating the validity of the model as a tool for predicting job physical stresses. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/24994/1/0000421.pdf
This prospective investigation was done to evaluate five strength and fitness measurements and the subsequent occurrence of back injuries in 1652 firefighters for the years 1971 to 1974. The prospective measurements included flexibility, isometric lifting strength, bicycle ergometer exercise measurements of two-minute recovery heart rate, diastolic blood pressure at a heart rate of 160 beats per minute and watts of effort required to sustain heart rate at 160. Three fitness and conditioning groups were established by multivariate ranking and regression techniques (259 high, 266 low, and 1127 middle) and the subsequent back injuries were tabulated for the three groups. The results showed a graded and statistically significant protective effect for added levels of fitness and conditioning (least fit, 7.1% injured; middle fit, 3.2% jured; and most fit, 0.8% injured). It was concluded that physical fitness and conditioning of firefighters are preventive of back injuries and that further investigations are warranted to study other injuries and physical fitness in this physically active occupational group.
Whatever the lifting method used, dynamic factors appear to have an effect on the safe realization of movement, and NIOSH guidelines recommend smooth lifting with no sudden acceleration effects. On the other hand, inertial forces may play an important role in the process of transfer of momentum to the load. The direction by which these inertial forces may affect the loadings on body structures and processes of energy transfers cannot be determined a priori. A biomechanical experiment was performed to examine if there were differences in the execution processes between a slow-continuous lift and an accelerated-continuous lift, and also between accelerated lifts either executed continuously or interrupted with a pause. The lifts were executed from a height of 15 cm to a height of 185 cm above the head and with two different loads (6.4 and 11.6 kg). Five experienced workers in manual materials handling were used as subjects. Films and force platforms recordings supplied the data; dynamic segmental analyses were performed to calculate net muscular moments at each joint; a planar single-muscle equivalent was used to estimate compression loadings at L5/S1; total mechanical work, joint work distribution, and energy transfers were determined from a kinetic approach based on the integration of joint power as a function of time. Analyses of variance with repeated measures were applied to the three treatments. The results showed that joint muscular moments, spinal loadings, mechanical work, and muscular utilization ratios were generally increased by the presence of acceleration without inducing benefits of improved energy transfers; therefore slower lifts with reduced acceleration may be safer when handling moderately heavy loads. The maximum values of kinematic and kinetic factors were generally not affected by the pause, but the occurrence of jerks in the movement (acceleration, ground forces, and muscular moments) suggests that the pause may not be indicated when considering total exposure to muscular exertion. Full consideration should be given to the dynamics of motion when assessing risk factors in working tasks.
Flexion-extension moments acting at the L5/S1 level and hip joints were calculated using three different techniques; a pure static analysis, a static analysis including the inertial force of the load, and a dynamic analysis. Ten subjects participated in the study and were asked to lift a box weighing either 50 N or 150 N, using a freestyle technique. The lifts were performed at normal and fast speed. The intra-subject lifting techniques were consistent when lifting the same loads. The moments predicted by the dynamic analysis and the static analysis were the same when holding weights in static postures. When performing the lifts, differences in the peak moments occurred between static and dynamic analyses. These differences were influenced by external load and by lifting speed. Taking the effect of the inertia of load into account in the static analysis resulted in an increase in the moment magnitude, but the predicted moment was still much less than in the dynamic analysis which yielded the largest moment magnitudes. The difference between dynamic and static analysis was greatest when lifting 50 N at fast speed; an 87% increase in L5/S1 moment and a 95% increase in hip moment was observed when replacing the pure static with a dynamic analysis.
A study was performed to determine the influence of load magnitude on the self selected technique of lifting. Specifically, it was hypothesized that with heavier weights a tendency would occur to lift more with the back and less with the legs. Flexion-extension moments at the L5/S1 level, hip and knee joints were calculated for subjects when lifting boxes weighing from 50 to 250 N. Lifts were performed using a freestyle technique at normal speed. The moment profiles (moment plotted vs time) were analyzed kinematically and as a function of the weight lifted. The kinematics of the lift changed as the weight increased. The moment at the L5/S1 level increased with increasing weight, however, the corresponding knee moment decreased. Thus, an inverse relationship was found between the moment at the L5/S1 level and the knee joint moment. An increase in weight lifted was also associated with an increase in the angular velocity at the knee while lifting. Apparently with heavier weights there is a tendency to extend the knees earlier during the lift than with lighter weights, confirming our hypothesis. This explains the reduced knee moment. Our findings lead to the hypothesis that quadriceps muscle strength limits the subjects' ability to lift with their knees flexed.
Flexion-extension moments occurring at the L5-S1 level of the spine were calculated when subjects lifted a 150 N box at slow, normal and fast speeds. Three methods of lifting were used: leg-lifting, back-lifting and free-style lifting. The peak moment increased linearly with increasing lifting speed. The increase was greatest for back lifts, but occurred with the other two lifting techniques as well. Inertial forces should be considered when analysing lifting tasks biomechanically. Excessive speed of lifting, including jerking, should be avoided.
Biomechanical models utilized for analysis of tasks that load the lumbar spine often predict the resultant moment, disc compression and sometimes shear. Usually the extensor muscular and ligament forces of the lumbar spine are assumed to act 5 cm posterior to a disc centre of rotation. This study has re-examined the generation and pathways of muscular force transmission within the extensor musculature. The effects on L4/L5 disc compression and shear estimates of an anatomically and biomechanically justifiable range of tissue moment arms, lines of force and force generating capacity of muscle, input to a computer model, have been determined. Results indicated that L4/L5 compression estimates could be reduced by up to 35% when the output from a more realistic anatomical model of the erector spinae muscle group was compared with that from the frequently reported and simplified single muscle equivalent with a 5 cm moment arm. The shear force estimates could be altered from more than 500 N (L4 tending to shear anteriorly on L5) to less than 200 N with L4 tending to shear posteriorly on L5. Using the combination of input variables considered by the authors to be most feasible to estimate compression, a single 'equivalent' extensor soft tissue moment arm of 7.5 rather than 5 cm would be needed to equate the compression. This simplification of course, does not accommodate the shear force estimate problem.
A simulated assembly-line task was constructed to investigate the metabolic cost and the pattern of muscular fatigue associated with selected arm lifts. Five healthy males lifted lead-filled cylinders five limes per minute in eight 1 hour sessions. In each session, the effect of varying the weight of the cylinders and the horizontal and vertical location or the point to which they were lifted was studied. Muscle fatigue was assessed from a frequency shift and rectified amplitude analysts of surface electromyographic records (EMG) of the deltoid, biceps, brachioradialis and upper trapezius muscles. Metabolic costs of the work were estimated from an analysis of heart rate and oxygen uptake. Additional measures included tests of strength decrement and ratings of perceived fatigue.The results indicated that the most fatiguing task variable was weight. At the heavier of the two levels, weight significantly increased the EMG amplitude of the deltoid, biceps and brachioradialis muscles. Significant increases in the EMG amplitude of the biceps were also found when the variable of height was adjusted to the higher of two levels. There was a similar effect on the EMG level of the deltoid muscle when reach was at a maximum. Although not as dramatic as the increases in EMG activity, both heart rate and oxygen uptake were significantly increased when the variables of height and weight were at their maximum levels, i.e. eye level and 80% maximum voluntary contraction ( MVC) The results provided a physiological basis for evaluating the effects of three task variables in lifting tasks involving upper extremity muscles
To quantify spinal stress biomechanical models are often used. Static models reveal the postural effects due to gravity, while dynamic models also take into account inertial factors. We used both dynamic and static models to evaluate the lumbosacral compression when 20 subjects lifted a box weighing 15 kg from a 10 cm high shelf to knuckle height with four lifting techniques. The mean peak acceleration of the load was 4·9 − 6·3ms, thus increasing the force at the hands by over 50%. The static peak compression was 3989−4650 N and the dynamic 5866−6629 N, the increase due to inertial factors being 33−60% depending on lifting technique.
Assessment of the effects of lifting on the low back has most frequently been done with the aid of static models. Many lifting movements appear to have substantial inertial components. It was of interest, therefore, to determine the size of the difference between statically and dynamically calculated lumbar moments during a demanding but not unusual manual lift observed in a metal fabrication industry. The results of several trials by four young men showed that the dynamic model resulted in peak L4/L5 moments 19% higher on average, with a maximum difference of 52%, than those determined from the static model. The technique adopted in the lift could minimize the difference. When the inertial forces of the load itself and the load weight were incorporated into an otherwise static model (quasi-dynamic) then the resulting L4/L5 moments exceeded those of the fully dynamic model by 25%. In many industrial tasks static analyses may severely underestimate the demands of dynamic lifts. These results show that a reasonably inexpensive approach in lifting task analysis is to measure the dynamic forces of the load on the hands and to use these in an otherwise static model. This results in a conservative assessment of the injury risk of lifts at least of the type reported in this study.
The goals of this study were to: evaluate the repeatability of a method of measuring trunk strength; measure isometric and isokinetic strength of trunk flexors, extensors and rotators; explore relationships among these muscle groups; and compare a torque to body weight adjustment measure versus lean body weight. One hundred twenty-five normal subjects (62 males, 63 females) were tested using a Cybex prototype trunk extension-flexion system. Sixty-seven subjects (25 males, 42 females) were tested using a prototype torso rotation unit. Fifty were tested on both devices. Results demonstrated that the strength data were reliable, with strength being greatest in extension. The following were also learned-torque output declined slightly with increased speed; extensor-flexor strength remained consistent from 18 to 44 years; extension-flexion ratios exceeded 1.1:1; left to right rotation ratios remained 1:1; there was no significant difference between torque adjusted to body weight or to lean body weight.
An experimental study based on a trigonometric, anthropometric model, was conducted on thirty-five healthy subjects to determine the relationship between knee and back forces during symmetric sagittal plane lifting. Total joint reaction forces for the knee and the back, along with their compressive and shear components, were calculated for each subject, as a function of the knee, back and ankle angles. The shear component was significantly higher in females than in males; the compressive component was significantly higher in males. Strong inverse correlations were found between the back and the knee forces on all subjects. Strong correlations were also found between subject anthropometry and minimum and maximum joint reaction forces. The magnitudes of both back and knee joint reaction forces should be considered in recommending the lift type and position, based upon individual worker anthropometry, and size and weight of the load to be lifted.
By measurement of intradiscal pressure in vitro, the hydrostatic properties of the nucleus pulposus of normal lumbar intervertebral disc were proven. The hydrodynamic properties seem to exist also in the somewhat degenerated disc, but not in the more severely deranged ones. Intravitally-performed measurements of disc pressure over the last 20 years in more than 100 individuals have demonstrated how the load on the lumbar disc varies with the position of the subject's body and during the performance of various tasks, both in standing and in sitting. Compared with the pressure of load in the upright standing position, reclining reduces the pressure by 50-80%, while unsupported sitting increases the load by 40%, forward leaning and weight lifting by more than 100%, and the position of forward flexion and rotation by 400%. Large augmentations in pressure were also observed in subject performing various commonly prescribed strengthening exercises.
This paper presents procedures to calculate the loads on the lumbar spine and the contraction forces in the trunk muscles that are likely to be produced by given physical activities.
In this study, we examined changes in kinematic and electromyographic (EMG) measurements of the coordination (ie, the relative timing of joint movements and muscle activity) of a squat-lifting task in response to lifting increasing loads.
Fifteen male industrial workers served as a sample of convenience.
Subjects lifted a weighted crate containing 15% to 75% of their maximum lifting capacity using a symmetrical squat-lift technique. Movement kinematics were obtained with videography. The relative phase between joint motions was derived. The EMG activity of the vastus lateralis muscle (VL) and the erector spinae muscle (ES) was recorded, and the relative timing of their onsets and peaks was estimated.
The relative phase of movement between joints such as the knee and lumbar spine changed in a quasi-linear fashion with increasing load during lifting but not during lowering. The relative time of onset of ES EMG activity and its peak activity changed in a manner consistent with the interjoint relative phase results. The timing of VL events were not affected by increasing the load.
Relatively continuous changes in interlimb coordination occur when increasing the load lifted from an initial squatting posture. Changes in EMG relative timing partially corroborate the kinematic evidence for changes in coordination with load scaling. The results indicate the need for further study to determine whether the observed changes in coordination are beneficial or detrimental to the musculoskeletal system. Clinicians should evaluate performance of this task under a range of task conditions.
Local thigh and low back perceived exertion (RPE), sagittal peak load moments, and leg and trunk muscular activity during repetitive submaximal lifting, with squat and stoop technique, were investigated.
This study analyzed changes in kinetic variables caused by changes in body movements during the lifting bouts, and the contribution of the biomechanical and physiologic variables to the variability in the local RPE responses.
Despite instructions that emphasize the "correct" lifting technique as the squat technique, the stoop technique is reported as more commonly used in practice. Few studies have investigated the effect of lifting technique on differentiated perceptual responses in repetitive lifting.
Ten experienced forest workers performed submaximal repetitive lifting bouts until steady-state VO2 was reached, using five different weight and frequency combinations with both squat and stoop techniques. Borg's scale was used for RPE measurements. Muscular activity in lumbar, hip, knee extensors, and knee flexors was recorded with surface electrodes. Kinematic data was obtained from electronic liquid-level sensors, and vertical ground reaction forces from a two-dimensional force plate.
Low back RPE was higher for stoop than for squat, whereas the opposite was true for thigh RPE. The total accountable variance (R2) for the biomechanical and physiologic variables to the RPE responses ranged from 0.25 (low back RPE in squat lifting) to 0.61-0.76 for the other assessments. During the time course in squat lifting at the highest frequency, the knee load moment decreased and the vertical ground reaction forces increased.
The study indicates that "movement strategies" to reduce the demand on the knee-extensor muscles were used during the squat lifting bouts at the highest frequencies, which combined with the relatively high assessed thigh exertions, leads to the hypothesis that quadriceps muscle exertion is the "weak link" for the squat technique. The study also indicates a discrepancy between the measured and perceived low back stress in squat repetitive lifting.
This study investigated the ability to predict maximal functional lifting capacity from peak isometric lumbar extension torque and submaximal lifting mechanics.
Peak isometric lumbar extension torques were measured on 26 healthy men and women, ages 18 to 39 years. In addition, their lifting mechanics were evaluated while they lifted a submaximal load. Each subject's maximal lifting capacity (kg) then was predicted from the peak torque and submaximal kinetic analysis using a linear regression model.
Mean values for the predicted and actual maximum weight the subjects lifted were not significantly different (50.3 +/- 15.6 kg and 48.5 +/- 17.0 kg, respectively, P > or = 0.05). The correlation between predicted and criterion values was high (r = 0.96), and the total error of the prediction was 5.1 kg, which represented 10.5% of the actual maximum value.
This multi-faceted functional assessment model involving biomechanical analysis of a submaximal lift and maximal isometric lumbar extension strength accurately predicted a subject's maximum functional lifting capacity.
A biomechanical analysis was performed of lifting before and after fatiguing the quadriceps muscles. The hypothesis tested was that when the quadriceps muscles were fatigued the lifter would change lifting technique from more of a squat (leg) lift to more of a stoop (back) lift to decrease the demand on the quadriceps muscles. The hypothesis was broadly supported, and three variables changed significantly with fatigue: trunk angular velocity, which increased, and knee moment integral and hip angles, which both decreased. These changes are all consistent with a change from more of a squat toward a stoop technique. The fact that the technique of lifting changes with quadriceps muscle fatigue underlines the importance of the physiologic condition of these muscles and suggests that rehabilitation of low-back-injured workers should include the quadriceps muscles. The amount of work performed should be controlled to avoid the development of local muscle fatigue and subsequent changes in performance.
Manual lifting techniques are commonly defined in terms of the postures adopted at the start of the lift. Quantitative definition is problematic, however, because the absolute joint angles adopted to lift an object are influenced by task parameters, such as the initial height of the load. We present an argument for the use of a postural index (the ratio of knee flexion from normal standing to the sum of ankle, hip, and lumbar vertebral flexion) to define the postures adopted at the start of lifting. Stooped postures adopted at the start of a lift correspond to postural indices close to 0, whereas full squat postures correspond to postural indices close to 1. We use angular kinematic data gathered from 71 individuals lifting loads of varying mass from a range of starting heights to illustrate the utility of this index. Although average absolute joint angles were influenced by load mass and initial load height, the average postural index remained unchanged. For example, changes in starting height from 9 cm to 63 cm accounted for between 19% and 67% of the variance in joint positions at the start of the lift but only 1% of the variance in average postural index. This suggests that the postural index provides a method of defining lifting posture that is independent of specific joint positions.
Co-ordination of various components of the human body during the course of lifting are very complex and difficult to control. This study hypothesized that strategies used to control the motion patterns of the external load may be applied to control co-ordination and also to control the level of compressive force on the lumbosacral joint. A simulation of lifting based on the optimization approach was introduced to generate three classes of unique dynamic motion patterns of the external load directed by three different objective functions. The first objective function was to maximize the smoothness of the motion pattern of the external load. The second objective function was to minimize the sudden change of the centre of gravity of the body-load system. The third objective was to minimize the integration over time of the sum of the square of the ratio of the predicted joint moments to the corresponding joint strength during the course of lifting. Eight subjects were recruited to perform 40 lifts using each of the three optimal motion patterns of the load. Compressive forces on the lumbosacral joint were computed and compared. The data showed with statistical significance that subjects using the motion patterns of the external load suggested by the first objective function had the lowest compressive force peaks. Thus, this study satisfied two goals: (1) it indexed and synthesized three motion patterns of the external load by three biomechanically unique objective functions, and (2) it established the association between the spinal loading and the control of the motion patterns of the external load during lifting.
Biomechanical exploration on dynamic modes of lifting Muscle fatigue asso-ciated with repetitive arm lifts: e!ects of height, weight and reach
- M Gagnon
- G Smyth
- D Habes
- W Carlson
- D Badger
Gagnon, M., Smyth, G., 1992. Biomechanical exploration on dynamic modes of lifting. Ergonomics 35, 329}345. Habes, D., Carlson, W., Badger, D., 1985. Muscle fatigue asso-ciated with repetitive arm lifts: e!ects of height, weight and reach. Ergonomics 28, 471}488.
Moment arms of spinal musculature deter-mined from CT scans Strength-limiting factors for the determination of frequent and infrequent lifting capacities
- S Kumar
Kumar, S., 1988. Moment arms of spinal musculature deter-mined from CT scans. Clinical Biomechanics 3, 137}144. Lee, Y.H., Chen, Y.L., 1996. Strength-limiting factors for the determination of frequent and infrequent lifting capacities. International Journal of Industrial Ergonomics 18, 51}60.
Disc pressure measurements Relationship between moments at the L5/S1 level, hip and knee joint when lifting Neuromuscu-lar coordination of squat lifting I: e!ect of load magnitude
- A Nachemson
- O D Schipplein
- Tra
- J H Mow
- G B J Andersson
- T P Andriacchi
Nachemson, A., 1981. Disc pressure measurements. Spine 6, 93}97. Schipplein, O.D., Tra"mow, J.H., Andersson, G.B.J., Andriacchi, T.P., 1990. Relationship between moments at the L5/S1 level, hip and knee joint when lifting. Journal of Biomechanics 23, 907}912. Scholz, J.P., Millford, J.P., McMillan, A.G., 1995. Neuromuscu-lar coordination of squat lifting I: e!ect of load magnitude. Physical Therapy 75, 44}57.
Analysis of loads on the lumbar spine Quan-ti"cation of lumbar function: I. Isometric and multispeed isokinetic trunk strength measures in sagittal and axial planes in normal subjects The e!ect of quadriceps fatigue on the tech-nique of lifting
- A B Schultz
- G B J Andersson
- S S Smith
- T G Mayer
- R J Gatchel
- T J H Becker
- O D Schipplein
- G J Novak
- G B J Andersson
Schultz, A.B., Andersson, G.B.J., 1981. Analysis of loads on the lumbar spine. Journal of Biomechanics 6, 76}82. Smith, S.S., Mayer, T.G., Gatchel, R.J., Becker, T.J., 1985. Quan-ti"cation of lumbar function: I. Isometric and multispeed isokinetic trunk strength measures in sagittal and axial planes in normal subjects. Spine 10, 757}764. Tra"mow, J.H., Schipplein, O.D., Novak, G.J., Andersson, G.B.J., 1993. The e!ect of quadriceps fatigue on the tech-nique of lifting. Spine 18, 364}367. Tsuang, Y.H., Schipplein, O.D., Tra"mow, J.H., Andersson, G.B.J., 1992. In#uence of body segment dynamics on loads at the lumbar spine during lifting. Ergonomics 35, 437}444.
A comparison of biomechanical characteristics of frequent and infrequent lifting activities
- Y L Chen
Chen, Y.L., 1996. A comparison of biomechanical characteristics
of frequent and infrequent lifting activities. Ph.D. Dissertation, National Taiwan University of Science and Technology, Taipei, Taiwan.
Model for static lifting
- Bejjani