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Longo, AR, Silva-Batista, C, Pedroso, K, de Salles Painelli, V, Lasevicius, T, Schoenfeld, BJ, Aihara, AY, de Almeida Peres, B, Tricoli, V, and Teixeira, EL. Volume load rather than resting interval influences muscle hypertrophy during high-intensity resistance training. J Strength Cond Res 36(6): 1554-1559, 2022-Interset rest interval has been proposed as an important variable for inducing muscle mass and strength increases during resistance training. However, its influence remains unclear, especially when protocols with differing intervals have equalized volume. We aimed to compare the effects of long (LI) vs. short rest interval (SI) on muscle strength (one repetition maximum [1RM]) and quadriceps cross-sectional area (QCSA), with or without equalized volume load (VL). Twenty-eight subjects trained twice a week for 10 weeks. Each subject's leg was allocated to 1 of 4 unilateral knee extension protocols: LI, SI, SI with VL -matched by LI (VLI-SI), and LI with VL-matched by SI (VSI-LI). A 3-minute rest interval was afforded in LI and VSI-LI protocols, while SI and VLI-SI employed a 1-minute interval. All subjects trained with a load corresponding to 80% 1RM. One repetition maximum and QCSA were measured before and after training. All protocols significantly increased 1RM values in post-training (p < 0.0001; LI: 27.6%, effect size [ES] = 0.90; VLI-SI: 31.1%, ES = 1.00; SI: 26.5%, ES = 1.11; and VSI-LI: 31.2%, ES = 1.28), with no significant differences between protocols. Quadriceps cross-sectional area increased significantly for all protocols in post-training (p < 0.0001). However, absolute changes in QCSA were significantly greater in LI and VLI-SI (13.1%, ES: 0.66 and 12.9%, ES: 0.63) than SI and VSI-LI (6.8%, ES: 0.38 and 6.6%, ES: 0.37) (both comparisons, p < 0.05). These data suggest that maintenance of high loads is more important for strength increases, while a greater VL plays a primary role for hypertrophy, regardless of interset rest interval.
... Based on acute data, it is logical to assert that long RIs may lead to superior RT outcomes by preserving TVL and quality of sets during individual training sessions. In support of this speculation, two recent publications have concluded that when the number of sets are matched, long RIs (3 min) are superior to short RIs (1 min) for chronic neuromuscular adaptations in untrained (19) and trained lifters (32). ...
... 1180 3-min (LONG) RIs on TVL, repetition performance, FI, and [La] during upper body (chest press) and lower body (leg press) exercise with low-intensity (75% of a 10-RM) in trained female lifters. These RI durations were selected because they have been used in previous studies (19,28,32). We hypothesized that TVL would be higher with LONG and that repetition decline, as measured by FI, would be greater with SHORT for both exercises. ...
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The purpose of this study was to investigate the effects of SHORT (1 min) and LONG (3 min) rest intervals (RI) on total volume lifted (TVL), repetition performance, fatigue index (FI), and blood lactate [La] during upper body (chest press) and lower body (leg press) exercise with low-intensity (75% of a 10-RM) in trained female lifters. Fourteen females (mean ± SD, age = 22.9 ± 5.4 years, training experience = 5.2 ± 2.5 years, height = 166.1 ± 6.9 cm, weight = 61.3 ± 5.1 kg, body fat % = 21.7 ± 3.3%) participated in this randomized, repeated-measures, cross-over design study. They performed four sets to failure on chest press (CP) and leg press (LP) under two conditions (SHORT and LONG RIs) in a counterbalanced manner. Paired-samples t-tests were used to analyze mean differences for TVL in CP and LP, separately. A 2 (exercise) x 2 (rest interval) repeated measures ANOVA was used to analyze mean differences in FI and average [La] values. A 2 (rest interval) x 4 (sets) repeated measures ANOVA was used to analyze mean differences in repetitions completed for each exercise. TVL for SHORT was significantly less when compared to LONG for both exercises. There was no significant difference in average [La] between RIs despite a greater FI in SHORT compared to LONG for both exercises. Lastly, [La] was higher during LP compared to CP irrespective of RI length. These results suggest that longer RIs are better for female lifters who want to optimize TVL with low-intensity resistance training. Metabolic stress, as measured by blood lactate, was greater during lower-body exercise.
... On these occasions, no other variable is abruptly changed besides the number of sets, repetitions, and training loads, and thus, volume-load is sufficient for the equalization of training volume between groups. Also, volume-load may serve as a measure to represent training volume when investigating the influence of movement velocity and rest interval between sets, as recently reported by Pearson et al. [24] and Longo et al. [25], respectively. Of note, muscle hypertrophy tends to be very similar when volume-load is similar between protocols in which these variables are manipulated [24][25][26][27][28][29][30][31][32][33]. ...
... Also, volume-load may serve as a measure to represent training volume when investigating the influence of movement velocity and rest interval between sets, as recently reported by Pearson et al. [24] and Longo et al. [25], respectively. Of note, muscle hypertrophy tends to be very similar when volume-load is similar between protocols in which these variables are manipulated [24][25][26][27][28][29][30][31][32][33]. ...
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Calculating resistance-training volume in programs focused on muscle hypertrophy is an attempt to quantify the external workload carried out, then to estimate the dose of stimulus imposed on targeted muscles. The volume is usually expressed in some variables that directly affected the total training work, such as the number of sets, repetitions, and volume-load. These variables are used to try to quantify the training work easily, for the subsequent organization and prescription of training programs. One of the main uses of measures of volume quantification is seen in studies in which the purpose is to compare the effects of different training protocols on muscle growth in a volume-equated format. However, it seems that not all measures of volume are always appropriate for equating training protocols. In the current paper, it is discussed what training volume is and the potentials and shortcomings of each one of the most common ways to equate it between groups depending on the independent variable to be compared (e.g., weekly frequency, intensity of load, and advanced techniques).
... Hardstyle kettlebell training does not follow all of the traditional resistance training protocols in relation to sets, repetitions, loads, or rest periods. It does however involve a significant within-session training load volume, which is beneficial for strength and hypertrophy [136]. High volume training may be advantageous or necessary in some cases [137,138], but improvements were still anticipated among participants with the lowest training load volume, as low volume resistance training can still improve muscle strength and functional performance in older adults, with no evidence of non-responsiveness [139]. ...
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The Ballistic Exercise of the Lower Limb (BELL) trial examined the efficacy and safety of a pragmatic hardstyle kettlebell training program in older adults. Insufficiently active men and women aged 59–79 years, were recruited to a 6-month repeated measures study, involving 3-months usual activity and 3-months progressive hardstyle kettlebell training. Health-related physical fitness outcomes included: grip strength [GS], 6-min walk distance [6MWD], resting heart rate [HR], stair-climb [SC], leg extensor strength [LES], hip extensor strength [HES], Sit-To-Stand [STS], vertical jump [CMVJ], five-times floor transfer [5xFT], 1RM deadlift, body composition (DXA), attendance, and adverse events. Sixteen males (68.8 ± 4.6 yrs, 176.2 ± 7.8 cm, 90.7 ± 11.0 kg, 29.2 ± 2.6 kg/m²) and sixteen females (68.6 ± 4.7 yrs, 163.9 ± 5.4 cm, 70.4 ± 12.7 kg, 26.3 ± 4.9 kg/m²) were recruited. Compliance with the supervised exercise program was very high (91.5%). Kettlebell training increased GS (R: MD = 7.1 kg 95% CI [4.9, 9.3], L: MD = 6.3 kg 95% CI [4.1, 8.4]), 6MWD (41.7 m, 95% CI [17.9, 65.5]), 1RM (16.2 kg, 95% CI [2.4, 30.0]), 30 s STS (3.3 reps, 95% CI [0.9, 5.7]), LES (R: MD = 61.6 N, 95% CI [4.4, 118.8]), HES (L: MD = 21.0 N,95% CI [4.2,37.8]), appendicular skeletal lean mass (MD = 0.65 kg, 95% CI [0.08, 1.22]), self-reported health change (17.1%, 95% CI [4.4, 29.8]) and decreased SC time (2.7 s, 95% CI [0.2, 5.2]), 5xFT time (6.0 s, 95% CI [2.2, 9.8]) and resting HR (7.4 bpm, 95% CI [0.7, 14.1]). There were four non-serious adverse events. Mean individual training load for group training sessions during the trial was 100,977 ± 9,050 kg. High-intensity hardstyle kettlebell training was well tolerated and improved grip strength and measures of health-related physical fitness in insufficiently active older adults. Trial registration: Prospectively registered: 20/08/2019, Australian New Zealand Clinical Trials Registry (ACTRN12619001177145).
... In contrast, TRAD consisted of 20 repetitions with a 2-s eccentric phase and 1-s concentric phase (2:1 s), which is commonly used for hypertrophy training (Lopes et al. 2017;Schoenfeld et al. 2016). For both protocols, five sets of belt squat were completed, 3-min rest intervals were provided between each set (Longo et al. 2020), and each set was completed close to concentric muscular failure ). To match TUT at 60 s, it was important that SLOW and TRAD sets were terminated after 10 and 20 repetitions, respectively. ...
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Purpose To investigate the effect of repetition tempo on cardiovascular and metabolic stress when time under tension (TUT) and effort are matched during sessions of lower body resistance training (RT). Methods In a repeated-measures, cross-over design, 11 recreationally trained females (n = 5) and males (n = 6) performed 5 sets of belt squats under the following conditions: slow-repetition tempo (SLOW; 10 reps with 4-s eccentric and 2-s concentric) and traditional-repetition tempo (TRAD; 20 reps with 2-s eccentric and 1-s concentric). TUT (60 s) was matched between conditions and external load was adjusted so that lifters were close to concentric muscular failure at the end of each set. External load, total volume load (TVL), impulse (IMP), blood lactate, ratings of perceived exertion (RPE), HR, and muscle oxygenation were measured. Results Data indicated that TVL (p < 0.001), blood lactate (p = 0.017), RPE (p = 0.015), and HR (p < 0.001) were significantly greater during TRAD while external load (p = 0.030) and IMP (p = 0.002) were significantly greater during SLOW. Whether it was expressed as minimal values or change scores, muscle oxygenation was not different between protocols. Conclusion When TUT is matched, TVL, cardiovascular stress, metabolic stress, and perceived exertion are greater when faster repetition tempos are used. In contrast, IMP and external load are greater when slower repetition tempos are used.
... However, within short time available-conditions, the TRI might be a viable option, since a higher TE was observed in the current study. In addition, in order to maintain higher VL values, coaches/practitioners may add an extra number of sets when performing TRI protocols (11). ...
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International Journal of Exercise Science 15(3): X-Y, 2022. The purpose of the present study was to assess performance and morphological acute responses to the tri-set (TRI) resistance-training system. In a random order, 18 subjects (years: 30.0 ± 5.6; weight: 81.8 ± 13.4 kg; height: 173 ± 6.2 cm; RT experience: 4.6 ± 1.7 years) performed 3 exercises targeting the pectoralis major muscle in two different experimental conditions: traditional system (TRAD) and TRI. The TRAD protocol referred to the completion of a single exercise set followed by a rest period. For the TRI protocol, one set of each exercise was performed sequentially with a minimal rest interval afforded (< 10 seconds). Both protocols were performed in 3 sets of 10RM. Pectoralis major muscle swelling (PMMS), volume load (VL), internal training load (ITL) and training efficiency (TE) were calculated and compared between both protocols. Despite the low VL (-19.3%; p < 0.001), larger values of PMMS (104.7%; p < 0.001), ITL (24.3%; p < 0.001) and TE (56.0%; p < 0.001) were observed during TRI compared to TRAD condition. In conclusion, the adoption of a TRI training protocol may induce distinct performance and morphological acute responses compared to TRAD, suggesting that resistance-trained subjects may experience a higher muscle swelling and intensity of effort with short time commitment when performing TRI system.
... Besides, another recent study equating volume load reported no differences in the volume of pectoralis major muscle measured by 3 T magnetic resonance imaging after training bench press at 4RM, 8RM, or 12RM during 10 weeks (2 days per week) (Kubo et al. 2021). In the same way, although 1-min inter-set rest induces more metabolite accumulation, resting 3 min triggers greater muscle growth when there are not significant differences in volume load (Schoenfeld et al. 2016b) and when performing the same sets (3 sets) without equalized volume load (Longo et al. 2020). Also, a study that compared 6 weeks of blood flow restriction training at 30% of 1RM to increase metabolic stress with traditional resistance training at 70% of 1RM found no differences in long-term myofibrillar MPS, ribosomal biogenesis, or muscle remodelling (Sieljacks et al. 2019). ...
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Resistance training is frequently performed with the goal of stimulating muscle hypertrophy. Due to the key roles motor unit recruitment and mechanical tension play to induce muscle growth, when programming, the manipulation of the training variables is oriented to provoke the correct stimulus. Although it is known that the nervous system is responsible for the control of motor units and active muscle force, muscle hypertrophy researchers and trainers tend to only focus on the adaptations of the musculotendinous unit and not in the nervous system behaviour. To better guide resistance exercise prescription for muscle hypertrophy and aiming to delve into the mechanisms that maximize this goal, this review provides evidence-based considerations for possible effects of neural behaviour on muscle growth when programming resistance training, and future neurophysiological measurement that should be tested when training to increase muscle mass. Combined information from the neural and muscular structures will allow to understand the exact adaptations of the muscle in response to a given input (neural drive to the muscle). Changes at different levels of the nervous system will affect the control of motor units and mechanical forces during resistance training, thus impacting the potential hypertrophic adaptations. Additionally, this article addresses how neural adaptations and fatigue accumulation that occur when resistance training may influence the hypertrophic response and propose neurophysiological assessments that may improve our understanding of resistance training variables that impact on muscular adaptations.
... In other words, less work can be performed on subsequent sets when exercising with limited inter-set recovery. In support of this theory, Longo et al. (133) demonstrated an impaired hypertrophic response with 1-versus 3-minute periods following 10 weeks of multi-set knee extension exercise. However, the differences neutralized when additional sets were performed in the short rest condition to equate volume-load. ...
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Hypertrophy can be operationally defined as an increase in the axial cross-sectional area of a muscle fiber or whole muscle, and is due to increases in the size of pre-existing muscle fibers. Hypertrophy is a desired outcome in many sports. For some athletes, muscular bulk and, conceivably, the accompanying increase in strength/power, are desirable attributes for optimal performance. Moreover, bodybuilders and other physique athletes are judged in part on their muscular size, with placings predicated on the overall magnitude of lean mass. In some cases, even relatively small improvements in hypertrophy might be the difference between winning and losing in competition for these athletes. This position stand of leading experts in the field synthesizes the current body of research to provide guidelines for maximizing skeletal muscle hypertrophy in an athletic population. The recommendations represent a consensus of a consortium of experts in the field, based on the best available current evidence. Specific sections of the paper are devoted to elucidating the constructs of hypertrophy, reconciliation of acute vs long-term evidence, and the relationship between strength and hypertrophy to provide context to our recommendations.
... It is needed to investigate how different load intensities and cuff pressures interact with each other and influence repetitions volume and muscular activation following BFR-RT to failure. In addition, given the relation between volumeload (repetitions x sets x load) and muscular gains (Schoenfeld & Grgic 2018;Longo et al. 2020), it is needed to be explored which magnitude of low-load intensity and cuff pressure may propitiate the greater volume to a common degree of muscular activation. ...
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The aim of the present study was to investigate the influence of intensity of load and cuff pressure on training volume and myoelectric activation during the knee extension exercise executed with and without blood flow restriction (BFR) to failure. Ten young men (22 ± 2 y), with at least six months of training experience, visited the laboratory on eight non-consecutive days with intervals of at least 48 hours between sessions. In the first two visits, one-repetition maximum (1RM) test and retest were performed in the unilateral knee extension exercise. In the subsequent six visits, the subjects performed resistance training sessions (4 sets to concentric failure) at different load intensities (30, or 40% of 1RM) and BFR pressures (0, 100, or 150mmHg). The restriction cuff was of 18-cm width and was positioned on the superior 1/3 of the thigh. Measures of training volume, and myoelectric activity from the vastus lateralis and vastus medialis via surface electromyographic, were recorded. During experimental sessions, it was observed that the use of BFR significantly reduced the training volume, independently of the load used. Less repetitions were performed with a restriction pressure of 150mmHg (47 ± 10) compared to 0mmHg (61 ± 15) and 100mmHg (59 ± 17), and with 30%1RM (50 ± 14) compared to 40%1RM (61 ± 15). For surface electromyography measures, no significant differences were observed between the conditions (P>0.05). In conclusion, the application of BFR to low-load knee extension exercise to failure led to lower training volume but did not influence myoelectric activity.
... Hardstyle kettlebell training does not follow all of the traditional resistance training protocols in relation to sets, repetitions, loads, or rest periods. It does however involve a significant within-session training load volume, which is beneficial for strength and hypertrophy (133) . High volume training may be advantageous or necessary in some cases (134,135) , but improvements were still anticipated among participants with the lowest training load volume, as low volume resistance training can still improve muscle strength and functional performance in older adults, with no evidence of non-responsiveness (136) . ...
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The Ballistic Exercise of the Lower Limb (BELL) trial examined efficacy and safety of a pragmatic hardstyle kettlebell training program in older adults. Insufficiently active men and women aged 59-79 years, were recruited to a 6-month repeated measures study, involving 3-months usual activity and 3-months progressive hardstyle kettlebell training. Health-related physical fitness outcomes included: grip strength [GS], 6-min walk distance [6MWD], resting heart rate [HR], stair-climb [SC], leg extensor strength [LES], hip extensor strength [HES], Sit-To-Stand [STS], vertical jump [CMVJ], five-times floor transfer [5xFT], 1RM deadlift, body composition (DXA), attendance, and adverse events. Sixteen males (68.8 ± 4.6 yrs, 176.2 ± 7.8 cm, 90.7 ± 11.0 kg, 29.2 ± 2.6 kg/m ² ) and sixteen females (68.6 ± 4.7 yrs, 163.9 ± 5.4 cm, 70.4 ± 12.7 kg, 26.3 ± 4.9 kg/m ² ) were recruited. Compliance to the supervised exercise program was very high (91.5%). Kettlebell training increased GS (R: MD = 7.1 kg 95% CI [4.9, 9.3], p < 0.001, L: MD = 6.3 kg 95% CI [4.1, 8.4], p < 0.001), 6MWD (41.7 m, 95% CI [17.9, 65.5], p < .001), 1RM (16.2 kg, 95% CI [2.4, 30.0], p = 0.013), 30s STS (3.3 reps, 95% CI [0.9, 5.7], p = 0.003), LES (R: MD = 61.6 N, 95% CI [4.4, 118.8], p = 0.028), HES (L: MD = 21.0 N, 95% CI [4.2, 37.8], p = 0.007), appendicular skeletal lean mass (MD = 0.65 kg, 95% CI [0.08, 1.22], p = 0.016), self-reported health change (17.1%, 95% CI [4.4, 29.8], p = 0.002) and decreased SC time (2.7 sec, 95% CI [0.2, 5.2], p = 0.025), 5xFT time (6.0 sec, 95% CI [2.2, 9.8], p < 0.001) and resting HR (7.4 bpm, 95% CI [0.7, 14.1], p = 0.032). There were four non-serious adverse events. Mean individual training load for group training sessions during the trial was 100,977 ± 9,050 kg. High-intensity hardstyle kettlebell training was well tolerated and improved grip strength and measures of health-related physical fitness in insufficiently active older adults.
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By reading this article, health and fitness professionals will learn: • There is a strong relationship between total volume load (TVL), muscular strength, and skeletal muscle hypertrophy. Resistance training with pyramid repetition schemes are an effective way to increase TVL during a training session. • Linear pyramid training (LPT), also known as DeLorme training, involves a systematic increase in intensity from set to set. Contrarily, reverse pyramid training (RPT), also known as Oxford training, involves a systematic decrease in intensity from set to set. • The literature consistently shows that RPT and LPT are both effective at increasing muscular strength; however, people may enjoy RPT more than LPT because the session feels easier as fatigue accumulates.
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We investigated the effects of low load resistance training to failure performed with different rest intervals on acute hormonal responses and long-term muscle and strength gains. In the acute study, 14 participants were assigned to either a short rest (S, 30 s) or long rest (L, 150 s) protocol at 40% one-repetition maximum. Blood samples were taken before and after workout. Both groups showed significant (p<0.05) increases in growth hormone and insulin-like growth factor 1 immediately postworkout. In the longitudinal study, the same protocol as in the acute study was performed 2 times/week for 8 weeks by 21 volunteers. Both groups showed significant increases in triceps (S: 9.8±8.8%, L: 10.6±9.6%, p<0.05) and thigh (S: 5.7±4.7%, L: 8.3±6.4%, p<0.05) cross-sectional area. Onerepetition maximum also significantly increased for the bench press (S: 9.9±6.9%, L: 6.5±5.8%, p<0.05) and squat (S: 5.2±6.7%, L: 5.4±3.5%, p<0.05). In conclusion, our results suggest that acute hormonal responses, as well as chronic changes in muscle hypertrophy and strength in low load training to failure are independent of the rest interval length.
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The present study investigated the effects of different intensities of resistance training (RT) on elbow flexion and leg press one-repetition maximum (1RM) and muscle cross-sectional area (CSA). Thirty men volunteered to participate in an RT programme, performed twice a week for 12 weeks. The study employed a within-subject design, in which one leg and arm trained at 20% 1RM (G20) and the contralateral limb was randomly assigned to one of the three conditions: 40% (G40); 60% (G60), and 80% 1RM (G80). The G20 started RT session with three sets to failure. After G20 training, the number of sets was adjusted for the other contralateral limb conditions with volume-matched. CSA and 1RM were assessed at pre, post-6 weeks, and post-12 weeks. There was time effect for CSA for the vastus lateralis (VL) (8.9%, 20.5%, 20.4%, and 19.5%) and elbow flexors (EF) (11.4%, 25.3%, 25.1%, and 25%) in G20, G40, G60, and G80, respectively (p > .05). G80 showed higher CSA than G20 for VL (19.5% vs. 8.9%) and EF (25% vs. 11.4%) at post-12 weeks (p < .05). There was time effect for elbow flexion and unilateral leg press strength for all groups post-12 weeks (p < .05). However, the magnitude of increase was higher in G60 and G80. In conclusion, when low to high intensities of RT are performed with volume-matched, all intensities were effective for increasing muscle strength and size; however, 20% 1RM was suboptimal in this regard, and only the heavier RT intensity (80% 1RM) was shown superior for increasing strength and CSA compared to low intensities.
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Although the effects of short versus long inter-set rest intervals in resistance training on measures of muscle hypertrophy have been investigated in several studies, the findings are equivocal and the practical implications remain unclear. In an attempt to provide clarity on the topic, we performed a systematic literature search of PubMed/MEDLINE, Scopus, Web of Science, Cochrane Library, and Physiotherapy Evidence Database (PEDro) electronic databases. Six studies were found to have met the inclusion criteria: (a) an experimental trial published in an English-language peer-reviewed journal; (b) the study compared the use of short (≤60 s) to long (>60 s) inter-set rest intervals in a traditional dynamic resistance exercise using both concentric and eccentric muscle actions, with the only difference in resistance training among groups being the inter-set rest interval duration; (c) at least one method of measuring changes in muscle mass was used in the study; (d) the study lasted for a minimum of four weeks, employed a training frequency of ≥2 resistance training days per week, and (e) used human participants without known chronic disease or injury. Current evidence indicates that both short and long inter-set rest intervals may be useful when training for achieving gains in muscle hypertrophy. Novel findings involving trained participants using measures sensitive to detect changes in muscle hypertrophy suggest a possible advantage for the use of long rest intervals to elicit hypertrophic effects. However, due to the paucity of studies with similar designs, further research is needed to provide a clear differentiation between these two approaches.
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In its last position stand about strength training, the American College of Sports Medicine recommends a rest interval (RI) between sets ranging between 1 and 3 min, varying in accordance with the objective. However, there is no consensus regarding the optimal recovery between sets, and most studies have investigated fixed intervals. Therefore, the aim of this study was to analyse the effects of fixed versus self-suggested RI between sets in lower and upper body exercises performance. Twenty-seven healthy subjects (26 ± 1.5; 75 ± 15 kg; 175 ± 12 cm) were randomly assigned into two groups: G1: lower body exercises and G2: upper body exercises. Squat and leg press 1 repetition maximum (1RM) were tested for the G1 and bench press and biceps curl 1RM for G2. After the 1RM tests, both groups performed three sets to concentric failure with 75% of 1RM in combination with different RIs (2 min or self-suggested) on separate days and the exercises performance was evaluated by the number of repetitions. The results demonstrated no significant differences in the number of repetitions between 2 min and self-suggested RIs that presented similar reductions with the sets progression. It was also shown that the self-suggested RI spent less time recovering than the 2 min RI group on average. This suggests that for individuals with previous experience, the self-suggested RI can be an effective option when using workloads commonly prescribed aiming hypertrophy. Also, the self-suggested RI can reduce the total training session duration, which can be a more time-effective strategy.
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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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It is generally accepted that neural factors play an important role in muscle strength gains. This article reviews the neural adaptations in strength, with the goal of laying the foundations for practical applications in sports medicine and rehabilitation. An increase in muscular strength without noticeable hypertrophy is the first line of evidence for neural involvement in acquisition of muscular strength. The use of surface electromyographic (SEMG) techniques reveal that strength gains in the early phase of a training regimen are associated with an increase in the amplitude of SEMG activity. This has been interpreted as an increase in neural drive, which denotes the magnitude of efferent neural output from the CNS to active muscle fibres. However, SEMG activity is a global measure of muscle activity. Underlying alterations in SEMG activity are changes in motor unit firing patterns as measured by indwelling (wire or needle) electrodes. Some studies have reported a transient increase in motor unit firing rate. Training-related increases in the rate of tension development have also been linked with an increased probability of doublet firing in individual motor units. A doublet is a very short interspike interval in a motor unit train, and usually occurs at the onset of a muscular contraction. Motor unit synchronisation is another possible mechanism for increases in muscle strength, but has yet to be definitely demonstrated. There are several lines of evidence for central control of training-related adaptation to resistive exercise. Mental practice using imagined contractions has been shown to increase the excitability of the cortical areas involved in movement and motion planning. However, training using imagined contractions is unlikely to be as effective as physical training, and it may be more applicable to rehabilitation. Retention of strength gains after dissipation of physiological effects demonstrates a strong practice effect. Bilateral contractions are associated with lower SEMG and strength compared with unilateral contractions of the same muscle group. SEMG magnitude is lower for eccentric contractions than for concentric contractions. However, resistive training can reverse these trends. The last line of evidence presented involves the notion that unilateral resistive exercise of a specific limb will also result in training effects in the unexercised contralateral limb (cross-transfer or cross-education). Peripheral involvement in training-related strength increases is much more uncertain. Changes in the sensory receptors (i.e. Golgi tendon organs) may lead to disinhibition and an increased expression of muscular force. Agonist muscle activity results in limb movement in the desired direction, while antagonist activity opposes that motion. Both decreases and increases in co-activation of the antagonist have been demonstrated. A reduction in antagonist co-activation would allow increased expression of agonist muscle force, while an increase in antagonist co-activation is important for maintaining the integrity of the joint. Thus far, it is not clear what the CNS will optimise: force production or joint integrity. The following recommendations are made by the authors based on the existing literature. Motor learning theory and imagined contractions should be incorporated into strength-training practice. Static contractions at greater muscle lengths will transfer across more joint angles. Submaximal eccentric contractions should be used when there are issues of muscle pain, detraining or limb immobilisation. The reversal of antagonists (antagonist-to-agonist) proprioceptive neuromuscular facilitation contraction pattern would be useful to increase the rate of tension development in older adults, thus serving as an important prophylactic in preventing falls. When evaluating the neural changes induced by strength training using EMG recording, antagonist EMG activity should always be measured and evaluated.
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