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Longer Interset Rest Periods Enhance Muscle Strength and Hypertrophy in Resistance-Trained Men
Abstract and Figures
The purpose of this study was to investigate the effects of short rest intervals normally associated with hypertrophy-type training versus long rest intervals traditionally used in strength-type training on muscular adaptations in a cohort of young, experienced lifters. Twenty-one young resistance-trained men were randomly assigned to either a group that performed a resistance training (RT) program with 1-minute rest intervals (SHORT) or a group that employed 3-minute rest intervals (LONG). All other RT variables were held constant. The study period lasted 8 weeks with subjects performing 3 total body workouts a week comprised of 3 sets of 8-12 repetition maximum (RM) of 7 different exercises per session. Testing was carried out pre- and post-study for muscle strength (1RM bench press and back squat), muscle endurance (50% 1RM bench press to failure), and muscle thickness of the elbow flexors, triceps brachii, and quadriceps femoris via ultrasound imaging. Maximal strength was significantly greater for both 1RM squat and bench press for LONG compared to SHORT. Muscle thickness was significantly greater for LONG compared to SHORT in the anterior thigh and a trend for greater increases was noted in the triceps brachii,(p = 0.06) as well. Both groups saw significant increases in local upper body muscle endurance with no significant differences noted between groups. The present study provides evidence that longer rest periods promote greater increases in muscle strength and hypertrophy in young resistance-trained men.
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... Resistance training guidelines recommend inter-set rest of long (>2 min) rather than short (<1 min) duration to increase muscle strength (Hill-Haas, Bishop, Dawson, Goodman & Edge, 2007;Schoenfeld, Pope, et al., 2016;Schoenfeld, Wilson, Lowery & Krieger, 2016). However, some studies show similar strength increases regardless of the inter-set rest (Ahtiainen, Pakarinen, Alen, Kraemer & Häkkinen, 2005;Buresh, Berg & French, 2009;Fink, Schoenfeld, Kikuchi & Nakazato, 2017;MacInnis, McGlory, Gibala & Phillips, 2017), but others show higher strength increases when using short inter-set rests (Villanueva, Lane & Schroeder, 2015). ...
... Such inconsistencies could be due to differences in the prescription of training variables and sample groups. Regarding training variables, studies exclusively investigated different durations of short (20 seconds to 1 min) and long (80 seconds to 5 min) rest intervals (Ahtiainen, et al., 2005;Fink, et al., 2017;Hill-Haas, et al., 2007) and differed between conditions for relative load, proximity to muscle failure and volume load (Buresh, et al., 2009;Fink, et al., 2017;Schoenfeld, Pope, et al., 2016). Regarding sample groups, some studies investigated physically inactive elderly persons (Villanueva, et al., 2015) or resistance-untrained individuals (Buresh, et al., 2009;Fink, et al., 2017;Piirainen, et al., 2011). ...
Resistance training is a widely used method to enhance muscle strength, with acute program variables influencing muscle adaptations. This study focused on the often-neglected variable of inter-set rest interval duration and its impact on muscle strength gains. Existing literature presents conflicting findings, with some studies advocating for longer rest intervals, while the others show comparable strength increases with shorter rests. Methodological differences in prescription and sample groups contributed to these inconsistencies. This study investigated the effect of short and long inter-set rests on maximal isokinetic strength gains of the upper and lower extremities during slow and fast angular velocities after eight weeks of resistance training. The research involved 26 healthy strength-trained males (age=20±1 year, body mass=81.5±8.8 kg, body height=184.4±6.1 cm) randomly assigned to G1m (1-minute rest) or G3m (3-minute rest). The resistance training programs were matched for all acute program variables, emphasizing the rest interval as the primary difference. Isokinetic dynamometry pre- and post-training assessed knee and elbow extensor and flexor maximal strength at 60º/s and 120º/s. The training program consisted of seven exercises performed at 70% 1RM until muscle failure three times per week over eight weeks. The most important result was that G3m, in contrast to G1m, led to a higher increase in peak torque of the knee (p=.037) and elbow extensors (p=.007) as well as the elbow flexors (p=.045) at 60º/s. Furthermore, G3m and G1m similarly increased the peak torque of the knee and elbow extensors and flexors at 120º/s and of the knee flexors at 60º/s (p>.138). In conclusion, the study suggests that strength training with longer inter-set rest intervals may lead to similar strength gains as strength training with shorter inter-set rest intervals. Nonetheless, individuals who prioritize maximizing their strength gains are advised to utilize longer rest intervals. However, shorter rest intervals may still yield significant strength enhancements, particularly for those who are limited by time.
... Follow-up short rest interval <1 min maintained during multiple 3 and 4 sets when resistance training high volume, however, longer rest interval >2 min progressively increased strength performance level for example back squat vs bench press maximum loading repetition accomplished (Schoenfeld et al., 2016). In generally, load repetition regimes within <90 of 1RM was used to multiple sets (2 and 5 set) progress maximum number of repetitions to per set evaluated on 3 and 5 min rest interval to short time periodization not cleared on different resistance training zones (Mangine et al., 2015;Grgic et al., 2018). ...
... Accordingly, maximum number of repetition both short and long rest intervals related to endurance zone working principle, however, not determined on rest interval (Willardson et al., 2006). Primarily zone strategies may be short rest (<1 min) constant set to high volume, however, long interval (>2 min) increased high strength and endurance performance level (Schoenfeld et al., 2016;Aycan et al., 2023). Other studies used to load range <90 of 1RM overload principle on multiple sets noted per set evaluated on 3 and 5 min rest interval to short time periodization (Mangine et al., 2015;Grgic et al., 2018;Aycan et al., 2023). ...
Continuum zone repetition training strategies are one of repetition manipulation both multiple set and repetition zone periodization on weightlifters. The present study was aimed to strength level on weightlift exercise condition of weightlifting athletes, deload repetition resistance training regimes involved in proper rest interval and repetition range by performing multiple set and longer rest interval within different maximize performance on light weeks. The experimental study was conducted to 2 olympic, 1 national, 6 professional weightlifters participated on age (16-21 years) this study. With study maximize performance condition over 3 week resistance training finished to weightlifters. Priority experimental pre-test and post-test outcomes after resistance training showed significant different (p < .05) in dynamic strength to countermovement jump shrug (p = .035; d = 0.69; = 17.78%). However, significant different in low load repetition failure to overhead press (p = .007; d = 0.86; = 5.56%), high load repetition failure to bent-over row (p = .017; d = 1.14; = 8.00%), low and high load repetition failure to countermovement jump shrug (p = .017; d = 1.17; = 13.78%-p = .048; d = 0.73; = 5.44%), in localize endurance not significant performance level to resistance exercise performance. However, isometric strength detected to overhead press (p = .016; d = 1.30; =-0.72%), bent-over row (p = .012; d = 1.67; =-0.51%) and countermovement jump shrug (p = .004; d = 2.45; =-0.48%) in weightlifters. Unsimilar longer rest interval multiple set configuration suggested to maximize strength gain on short time deload repetition training regimes by manipulated repetition and set addition rest interval currently manipulation of weightlifters.
... In a typical RT session, multiple sets of various lower-and upper-body exercises are performed, with rest periods between sets ranging from 1 to 5 min depending on the specific training goals [3]. Researchers have recommended inter-set rest periods of at least 3 min to optimize adaptations in maximal strength, maximal power, and athletic performance [4][5][6]. Longer inter-set rest periods (3 to 5 min) facilitate physiological and neuromuscular recovery (e.g., phosphocreatine (PCr) resynthesis), ensuring sustained high-quality performance throughout the RT session, which is known to be a critical factor for inducing training adaptations. However, to enhance training efficiency and alleviate monotony, it is feasible to integrate other physical activities during interset rest intervals without adversely affecting mechanical performance in the main exercises prescribed in the training session [7,8]. ...
Background
Paired sets and alternative set configurations (e.g., cluster sets) are frequently employed by strength and conditioning practitioners; however, their synergistic impact remains underexplored in research. This study aimed to elucidate whether the set configuration used in a lower-body exercise affects mechanical performance during paired sets of upper-body exercises.
Methods
Twenty-one resistance-trained individuals (14 men and 7 women) randomly completed three experimental sessions that involved four sets of five repetitions at 75%1RM during both the bench press and bench pull exercises. The three experimental sessions varied solely in the activity conducted during the inter-set rest periods of each upper-body exercise: (i) Traditional squat – six squat repetitions without intra-set rest at 65%1RM; (ii) Rest redistribution squat – two clusters of three repetitions of the squat exercise at 65%1RM with 30 s of intra-set rest; and (iii) Passive rest – no exercise.
Results
The rest redistribution set configuration allowed the sets of the squat exercise to be performed at a faster velocity than the traditional set configuration (p = 0.037). However, none of the mechanical variables differed between the exercise protocols neither in the bench press (p ranged from 0.279 to 0.875) nor in the bench pull (p ranged from 0.166 to 0.478).
Conclusions
Although rest redistribution is an effective strategy to alleviate fatigue during the sets in which it is implemented, it does not allow subjects to perform better in subsequent sets of the training session.
... Athletes in the present study trained to failure in every set using a moderately heavy 10RM load, which, although not generally a recommended RT approach, can be used as a method to assess differences in capacity, i.e., how much work the athlete is able to perform over the course of a training session. Chronic RT adaptations such as maximal strength and hypertrophy appear to favor longer interset rest periods [Schoenfeld et al. 2015]. Although longer breaks are conducive to more intra-session work and thus potentially greater stimuli and subsequent adaptations, it could be speculated that post-session fatigue may be comparable or even more pronounced compared to shorter breaks. ...
Background. Grip performance is a fundamental attribute in grappling sports. Problem and aim. Concurrent training may impact physical function and thus sport-specific training performance. We investigated whether resistance training (RT) exercise order affected repetition performance and rating of perceived exertion (RPE), and quantified the impact of RT on gripping in Brazilian jiu-jitsu (BJJ) grapplers. Material and methods. Twelve BJJ athletes completed two RT sessions in a random order. The sessions incorporated the same four exercises in either alternated order (AO) or grouped order (GO). Three sets were performed to failure using a 10-repetition maximum (10RM) load. The maximum number of repetitions (MNR) for each set determined repetition performance, and RPE was used to assess fatigue. Grip performance was measured with a maximum static lift (MSL) at baseline and post RT. Results. In both protocols, MNR decreased significantly over time, with no significant protocol × set interaction (p > 0.05). RPE increased over time, with no protocol × set interaction (p > 0.05). Both protocols resulted in reduced MSL (p < 0.001), with no difference in magnitude (p > 0.05). Total training volume, average RPE, and session perceived load (average RPE × session duration) did not differ between protocols (p > 0.05). Conclusions. Exercise order in short, full-body RT programs did not acutely influence repetition performance or perceptions of fatigue in these athletes. Grip endurance was severely compromised following RT, independent of exercise order. Grapplers doing same-day concurrent training should be mindful of the immediate impact of RT on gripping ability.
... Regular resistance training (RT) is considered one of the effective means to promote health. 1,2 RT can not only enhance muscle mass, 3,4 strength, and exercise performance 5,6 but also effectively improve body composition and reduce body weight. [7][8][9] The volume, intensity, ability, and number of muscle groups trained per training session are associated with optimal RT frequency. ...
Background
Resistance training (RT) and protein supplementation have beneficial effects on the human body. However, it is unknown if RT's health-promoting benefits are enhanced by food-borne protein, such as cheese supplements. This study investigated at how the body composition, lipid profile, muscle strength and intestinal microbiota changed following four weeks of RT combined with cheese supplementation.
Methods
Thirty-five male and untrained adults were divided into 4 groups [control group (CON), low-dose group (LG), medium-dose group (MG), and high-dose group (HG)] and underwent a 4-week RT (3 times/week) in combination with cheese supplementation. Participants received 108 g (LG), 216 g (MG), or 324 g (HG) of cheese on the day of RT, and each serving (108 g) of cheese contained 6.7 g of food-borne protein. The RT program was a whole-body program with movements such as chest presses, leg presses, seated rowing, knee extensions and triceps pushdown. The exercise consisted of 3 sets of 8–12 repetitions at 70%RM, with a 120-s break in between. Body parameters (body composition, lipid profile and muscle strength) were assessed at baseline and after the 4 weeks of the intervention. The feces sample was taken every weekend. A two-way (group × time) mixed-design ANOVA was used to examine the body parameters. Independent one-way ANOVA was used to analyze the differences between groups in baseline characteristics and different values of each parameter.
Results
HDL-C level was higher in MG than in LG. In comparison to LG, MG had lower levels of total cholesterol, low-density lipoprotein cholesterol, body weight, body mass index, body fat mass and body fat percentage. However, there was no difference in muscle strength between in the four groups. The abundance of Actinobacteria was higher in LG and Erysipelotrichaceae was lower in MG and HG.
Conclusion
The findings suggest that cheese could be a readily available food-borne protein supplement to enhance the beneficial effects of RT on health. It may improve body composition and lipid profile by altering the proportion of intestinal microbiota. During the 4-week RT intervention, 13.4 g of foodborne protein in the form of cheese 3 times per week was the ideal dosage.
... MVT. Longer inter-set rest periods and higher MVTs (i.e., leaving more repetitions in reserve) can effectively reduce fatigue during resistance training sessions. Such strategic manipulation of training variables has been proven to optimize longterm adaptations in maximum strength and neuromuscular performance (Pareja-Blanco, Alcazar, et al., 2020;B. J. Schoenfeld et al., 2016). Additionally, it mitigates the acute hormonal disruptions and muscle damage that typically follow a resistance training session, thereby facilitating improved neuromuscular performance during other physical activities within the 48 h post-exercise (Gonzalez-Badillo et al., 2016). ...
This study examined the influence of inter-set rest periods of 1 (R1), 3 (R3) and 5 (R5) minutes on the number of repetitions completed before exceeding the minimum velocity thresholds of 0.45 m⋅s −1 (MVT 0.45) and 0.35 m⋅s −1 (MVT 0.35) during the bench press exercise. Twenty-three physically active individuals, 15 men and eight women, randomly completed six testing sessions consisting of four sets of the bench press exercise performed with maximal intent against 75% of the one-repetition maximum. Testing sessions differed in the length of inter-set rest periods (R1, R3, and R5) and MVT applied (MVT 0.45 and MVT 0.35). The number of repetitions was lower using shorter inter-set rest periods (R1 < R3 < R5), but R3 was more similar to R1 and R5 using MVT 0.45 and MVT 0.35 , respectively. The fastest velocity of the set was reduced with the increment in the number of sets for the three protocols using MVT 0.35 (greater reduction for shorter rest periods), but it was only reduced for R1 when using MVT 0.45. The results suggest that, to maintain bench press mechanical performance, 5-min inter-set rest periods are necessary when sets are terminated close to failure (MVT 0.35), while 3 min may suffice when sets are terminated farther from failure (MVT 0.45).
The aim of the present study was to compare the effect of different rest intervals between sets of the leg press exercise on total volume, time under tension and ratings of perceived exertion (RPE). Eighteen young women (23.9±3.8 years) performed two experimental sessions, at least 72 hours apart, in a balanced cross-over design. In each session, the participants performed three sets until voluntary exhaustion, with loads that corresponded to 10-12 maximum repetitions, using RI of the two-minute (RI-2) or four-minutes (RI-4). The session performed with RI-4 showed a total volume (∑ repetitions x load) and time under tension (∑ total time duration of the three sets) statistically higher when compared to the RI-2 session (P < 0.05). No statistically significant difference was observed in RPE between sets of both experimental sessions (P < 0.05). The session performed with RI-4 showed a training load (RPE assessed 30 minutes after experimental sessions x duration of the session) statistically higher compared to the session with RI-2 (P < 0.05). The findings of the present study suggest the use of different RI between sets appeared to influence muscle performance and ratings of perceived exertion.
Background: Rapid regeneration after intense exercise is essential for competitive athletes. Based on this assumption, supplementa-tion strategies, focusing on food supplements, are increasing to improve the recovery processes. One such supplement is cannabi-diol (CBD) which is gaining more attention in competitive sports. However, the evidence is still lacking and there are no data available about the effect of a short-term chronic application. Methods: A three-arm double-blind cross-over study was conducted to determine the effects of two different CBD products on performance, muscle damage and inflammatory processes in well-trained athletes. In total 17 subjects took successfully part in this study. Each subject underwent the six-day, high-intensity training protocol three times. After each training session, each subject took either a placebo or a CBD product (60 mg of oil or solubilisate). Between the intervention phases, at least four weeks of washout period was conducted. Before and after the training protocols the performance capacity in countermovement jump (CMJ), back squat (BS), bench press (BP) and 1-mile run were measured and biomar-kers for muscle damage (creatine kinase, myoglobin), inflammatory processes (interleukin 6 and 10) and immune cell activity (ratios of neutrophil granulocytes, lymphocytes and, platelets) were analyzed. For statistical analyses, the current version of R and a linear mixed model was used. Results: It could identify different effects of the training protocol depending on performance level (advanced or highly advanced athletes) (p < .05). Regardless of the performance level, muscle damage and a reduction in performance could be induced by the training protocol. Only CBD oil was associated with a reduction in myoglobin concentration (p < .05) in ARTICLE HISTORY
The purpose of this study was to investigate the effects of training muscle groups 1 day per week using a split-body routine versus 3 days per week using a total-body routine on muscular adaptations in well-trained men. Subjects were 20 male volunteers (height = 1.76 ± 0.05 m; body mass = 78.0 ± 10.7 kg; age = 23.5 ± 2.9 years) recruited from a university population. Participants were pair-matched according to baseline strength and then randomly assigned to 1 of 2 experimental groups: a split-body routine (SPLIT) where multiple exercises were performed for a specific muscle group in a session with 2-3 muscle groups trained per session (n = 10), or; a total-body routine (TOTAL), where 1 exercise was performed per muscle group in a session with all muscle groups trained in each session (n = 10). Subjects were tested pre- and post-study for 1 repetition maximum strength in the bench press and squat, and muscle thickness of forearm flexors, forearm extensors, and vastus lateralis. Results showed significantly greater increases in forearm flexor muscle thickness for TOTAL compared to SPLIT. No significant differences were noted in maximal strength measures. The findings suggest a potentially superior hypertrophic benefit to higher weekly resistance training frequencies.
The study's purpose was to compare the response of performing 1, 3 and 5-sets on measures of performance and muscle hypertrophy. Forty eight men, with no weight training experience, were randomly assigned to one of three training groups, 1-SET, 3-SETS, 5-SETS, or control group (CG). All training groups performed three resistance training sessions per week for six months. The 5RM for all training groups increased in the bench press (BP), front lat pull down (LPD), shoulder press (SP) and leg press (LP) (p≤0.05), with the 5RM increases in the BP and LPD being significantly greater for 5-SETS compared to the other training groups (p ≤ 0.05). BP 20RM in the 3- and 5-SETS groups significantly increased with the increase being significantly greater than the 1-SET group and the 5-SETS group increase being significantly greater than the 3-SETS group (p≤0.05). LP 20RM increased in all training groups (p≤0.05), with the 5-SETS group showing a significantly greater increase than the 1-SET group (p≤0.05). The 3- and 5-SETS groups significantly increased elbow flexor muscle thickness (MT) with the 5-SETS increase being significantly greater than the other two training groups (p≤0.05). The 5-SETS group significantly increased elbow extensor MT with the increase being significantly greater than the other training groups (p≤0.05). All training groups decreased percent body fat, increased fat free mass and vertical jump ability (p≤0.05), with no differences between groups. The results demonstrate a dose response for the number of sets per exercise and a superiority of multiple sets compared to a single set per exercise for strength gains, muscle endurance and upper arm muscle hypertrophy.
Due to a scarcity of longitudinal trials directly measuring changes in muscle girth, previous recommendations for inter-set rest intervals in resistance training programs designed to stimulate muscular hypertrophy were primarily based on the post-exercise endocrinological response and other mechanisms theoretically related to muscle growth. New research regarding the effects of inter-set rest interval manipulation on resistance training-induced muscular hypertrophy is reviewed here to evaluate current practices and provide directions for future research. Of the studies measuring long-term muscle hypertrophy in groups employing different rest intervals, none have found superior muscle growth in the shorter compared with the longer rest interval group and one study has found the opposite. Rest intervals less than 1 minute can result in acute increases in serum growth hormone levels and these rest intervals also decrease the serum testosterone to cortisol ratio. Long-term adaptations may abate the post-exercise endocrinological response and the relationship between the transient change in hormonal production and chronic muscular hypertrophy is highly contentious and appears to be weak. The relationship between the rest interval-mediated effect on immune system response, muscle damage, metabolic stress, or energy production capacity and muscle hypertrophy is still ambiguous and largely theoretical. In conclusion, the literature does not support the hypothesis that training for muscle hypertrophy requires shorter rest intervals than training for strength development or that predetermined rest intervals are preferable to auto-regulated rest periods in this regard.
The purpose of this study was to investigate the time course of hypertrophic adaptations in both the upper arm and trunk muscles following high-intensity bench press training. Seven previously untrained young men (aged 25 ± 3 years) performed free-weight bench press training 3 days (Monday, Wednesday and Friday) per week for 24 weeks. Training intensity and volume were set at 75% of one repetition maximum (1-RM) and 30 repetitions (3 sets of 10 repetitions, with 2-3 min of rest between sets), respectively. Muscle thickness (MTH) was measured using B-mode ultrasound at three sites: the biceps and triceps brachii and the pectoralis major. Measurements were taken a week prior to the start of training, before the training session on every Monday and 3 days after the final training session. Pairwise comparisons from baseline revealed that pectoralis major MTH significantly increased after week-1 (p = 0.002), triceps MTH increased after week-5 (p = 0.001) and 1-RM strength increased after week-3 (p = 0.001) while no changes were observed in the biceps MTH from baseline. Significant muscle hypertrophy was observed earlier in the chest compared to that of the triceps. Our results indicate that the time course of the muscle hypertrophic response differs between the upper arm and chest.
Nutrient timing is a popular nutritional strategy involves the consumption of combinations of nutrients--primarily protein and carbohydrate--in and around an exercise session. Some have claimed that this approach can produce dramatic improvements in body composition. It has even been postulated that the timing of nutritional consumption may be more important than the absolute daily intake of nutrients. The post-exercise period is widely considered the most critical part of nutrient timing. Theoretically, consuming the proper ratio of nutrients during this time not only initiates the rebuilding of damaged muscle tissue and restoration of energy reserves, but it does so in a supercompensated fashion that enhances both body composition and exercise performance. Several researchers have made reference to an anabolic "window of opportunity" whereby a limited time exists after training to optimize training-related muscular adaptations. However, the importance - and even the existence - of a post-exercise 'window' can vary according to a number of factors. Not only is nutrient timing research open to question in terms of applicability, but recent evidence has directly challenged the classical view of the relevance of post-exercise nutritional intake with respect to anabolism. Therefore, the purpose of this paper will be twofold: 1) to review the existing literature on the effects of nutrient timing with respect to post-exercise muscular adaptations, and; 2) to draw relevant conclusions that allow practical, evidence-based nutritional recommendations to be made for maximizing the anabolic response to exercise.
Purpose:
To determine if 8 weeks of periodized strength resistance training (RT) utilizing relatively short rest interval lengths (RI) in between sets (SS) would induce greater improvements in body composition and muscular performance, compared to the same RT program utilizing extended RI (SL).
Methods:
22 male volunteers (SS: n = 11, 65.6 ± 3.4 years; SL: n = 11, 70.3 ± 4.9 years) were assigned to one of two strength RT groups, following 4 weeks of periodized hypertrophic RT (PHRT): strength RT with 60-s RI (SS) or strength RT with 4-min RI (SL). Prior to randomization, all 22 study participants trained 3 days/week, for 4 weeks, targeting hypertrophy; from week 4 to week 12, SS and SL followed the same periodized strength RT program for 8 weeks, with RI the only difference in their RT prescription.
Results:
Following PHRT, all study participants experienced increases in lean body mass (LBM) (p < 0.01), upper and lower body strength (p < 0.001), and dynamic power (p < 0.001), as well as decreases in percentage body fat (p < 0.05). Across the 8-week strength RT phase, SS experienced significantly greater increases in LBM (p = 0.001), flat machine bench press 1-RM (p < 0.001), bilateral leg press 1-RM (p < 0.001), narrow/neutral grip lat pulldown (p < 0.01), and Margaria stair-climbing power (p < 0.001), compared to SL.
Conclusions:
This study suggests 8 weeks of periodized high-intensity strength RT with shortened RI induces significantly greater enhancements in body composition, muscular performance, and functional performance, compared to the same RT prescription with extended RI, in older men. Applied professionals may optimize certain RT-induced adaptations, by incorporating shortened RI.
Purpose:
Muscle hypertrophy in response to resistance training has been reported to occur nonuniformly along the length of the muscle. The purpose of the present study was to examine whether the regional difference in muscle hypertrophy induced by a training intervention corresponds to the regional difference in muscle activation in the training session.
Methods:
Twelve young men participated in a training intervention program for the elbow extensors with a multijoint resistance exercise for 12 wk (3 d · wk(-1)). Before and after the intervention, cross-sectional areas of the triceps brachii along its length were measured with magnetic resonance images. A series of transverse relaxation time (T2)-weighted magnetic resonance images was recorded before and immediately after the first session of training intervention. The T2 was calculated for each pixel within the triceps brachii. In the images recorded after the session, the number of pixels with a T2 greater than the threshold (mean + 1 SD of T2 before the session) was expressed as the ratio to the whole number of pixels within the muscle and used as an index of muscle activation (percent activated area).
Results:
The percent activated area of the triceps brachii in the first session was significantly higher in the middle regions than that in the most proximal region. Similarly, the relative change in cross-sectional area induced by the training intervention was also significantly greater in the middle regions than the most proximal region.
Conclusion:
The results suggest that nonuniform muscle hypertrophy after training intervention is due to the region-specific muscle activation during the training session.