Effects of different intensities of resistance training with equated volume load on muscle strength and hypertrophy

Strength Training Intensity and Volume Affect Performance of Young Kayakers/Canoeists

Purpose

The aim of this study was to compare the effects of moderate intensity, low volume (MILV) vs. low intensity, high volume (LIHV) strength training on sport-specific performance, measures of muscular fitness, and skeletal muscle mass in young kayakers and canoeists.

Methods

Semi-elite young kayakers and canoeists (N = 40, 13 ± 0.8 years, 11 girls) performed either MILV (70–80% 1-RM, 6–12 repetitions per set) or LIHV (30–40% 1-RM, 60–120 repetitions per set) strength training for one season. Linear mixed-effects models were used to compare effects of training condition on changes over time in 250 and 2,000 m time trials, handgrip strength, underhand shot throw, average bench pull power over 2 min, and skeletal muscle mass. Both between- and within-subject designs were used for analysis. An alpha of 0.05 was used to determine statistical significance.

Results

Between- and within-subject analyses showed that monthly changes were greater in LIHV vs. MILV for the 2,000 m time trial (between: 9.16 s, SE = 2.70, p < 0.01; within: 2,000 m: 13.90 s, SE = 5.02, p = 0.01) and bench pull average power (between: 0.021 W⋅kg^–1, SE = 0.008, p = 0.02; within: 0.010 W⋅kg^–1, SE = 0.009, p > 0.05). Training conditions did not affect other outcomes.

Conclusion

Young sprint kayakers and canoeists benefit from LIHV more than MILV strength training in terms of 2,000 m performance and muscular endurance (i.e., 2 min bench pull power).

Safety, Fear and Neuromuscular Responses after a Resisted Knee Extension Performed to Failure in Patients with Severe Haemophilia

Background: low–moderate intensity strength training to failure increases strength and muscle hypertrophy in healthy people. However, no study assessed the safety and neuromuscular response of training to failure in people with severe haemophilia (PWH). The purpose of the study was to analyse neuromuscular responses, fear of movement, and possible adverse effects in PWH, after knee extensions to failure. Methods: twelve severe PWH in prophylactic treatment performed knee extensions until failure at an intensity of five on the Borg CR10 scale. Normalised values of amplitude (nRMS) and neuromuscular fatigue were determined using surface electromyography for the rectus femoris, vastus medialis, and vastus lateralis. After the exercise, participants were asked about their perceived change in fear of movement, and to report any possible adverse effects. Results: Patients reported no adverse effects or increased fear. The nRMS was maximal for all the muscles before failure, the median frequency decreased, and wavelet index increased during the repetitions. The vastus lateralis demonstrated a higher maximum nRMS threshold and earlier fatigue, albeit with a lower and more progressive overall fatigue. Conclusions: severe PWH with adequate prophylactic treatment can perform knee extensions to task failure using a moderate intensity, without increasing fear of movement, or adverse effects.

Resistance training intervention performed with different muscle action durations influences the maximal dynamic strength without promoting joint-angle specific strength gains

The present study investigated the effect of 10-week matched (range of motion, volume, intensity, rest, and repetition duration) training protocols with varying muscle action duration (MAD) on maximal voluntary isometric contraction (MVIC) test at eight different knee angles and one-repetition maximum (1RM) test after in seated knee extensor machine. Forty women were allocated into one control and three training groups with varying MAD: 5C1E (5s concentric action [CON] and 1s eccentric action [ECC]), 3C3E (3s CON and 3s ECC), and 1C5E (1s CON and 5s ECC). All training groups (5C1E, 3C3E, and 1C5E) showed a greater relative response in 1RM performance than the control group (0.1 ± 3.5%, p ≤ 0.05). The 1C5E group presented greater relative increases in the 1RM performance (22.1 ± 11.6%) compared to 5C1E (13.6 ± 9.2%; p ≤ 0.05) and 3C3E (14.1 ± 5.5%, p ≤ 0.05) groups. The training groups increased the MVIC performance more than the control group (p ≤ 0.05), although there were no significant differences between the training groups. This study demonstrated that isoinertial resistance training protocols with shorter CON MAD showed greater maximum dynamic strength performance response than matched training protocols with other MAD configurations. However, the configuration of MAD did not induce angle-specificity to increase the maximum isometric strength.

Resistance Training Load Effects on Muscle Hypertrophy and Strength Gain: Systematic Review and Network Meta-analysis

PURPOSE

This study aimed to analyze the effect of resistance training (RT) performed until volitional failure with low, moderate, and high loads on muscle hypertrophy and muscle strength in healthy adults and to assess the possible participant-, design-, and training-related covariates that may affect the adaptations.

METHODS

Using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, MEDLINE, CINAHL, EMBASE, SPORTDiscus, and Web of Science databases were searched. Including only studies that performed sets to volitional failure, the effects of low- (>15 repetitions maximum (RM)), moderate- (9-15 RM), and high-load (≤8 RM) RTs were examined in healthy adults. Network meta-analysis was undertaken to calculate the standardized mean difference (SMD) between RT loads in overall and subgroup analyses involving studies deemed of high quality. Associations between participant-, design-, and training-related covariates with SMD were assessed by univariate and multivariate network meta-regression analyses.

RESULTS

Twenty-eight studies involving 747 healthy adults were included. Although no differences in muscle hypertrophy between RT loads were found in overall (P = 0.113-0.469) or subgroup analysis (P = 0.871-0.995), greater effects were observed in untrained participants (P = 0.033) and participants with some training background who undertook more RT sessions (P = 0.031-0.045). Muscle strength improvement was superior for both high-load and moderate-load compared with low-load RT in overall and subgroup analysis (SMD, 0.60-0.63 and 0.34-0.35, respectively; P < 0.001-0.003), with a nonsignificant but superior effect for high compared with moderate load (SMD, 0.26-0.28, P = 0.068).

CONCLUSIONS

Although muscle hypertrophy improvements seem to be load independent, increases in muscle strength are superior in high-load RT programs. Untrained participants exhibit greater muscle hypertrophy, whereas undertaking more RT sessions provides superior gains in those with previous training experience.

Moderators of strength gains and hypertrophy in resistance training: A systematic review and meta-analysis

This meta-analysis investigated the role of resistance training (RT) moderators on strength and muscle mass gains in untrained young (YG) and older (OG) adults. Electronic databases were searched for randomised controlled trials simultaneously assessing muscle strength and mass. Effect sizes (ES) reflecting improvements in strength and muscle mass were found for all moderators in YG and OG (ES 0.25- to 1.72;p < 0.05), excepting muscle mass in YG after RT was performed with <3 sets/exercise. Strength gains (p < 0.001) were greater in non-periodised vs. periodised RT in YG (ES 1.72 vs. 1.05) and OG (1.40 vs. 0.74). ES in OG was greater (p < 0.04) when RT included non-failure vs. failure repetitions (1.35 vs. 0.96), 3 vs. >3 sets/exercise (1.30 vs. 0.90), ≥3 vs. <3 days/week (1.70 vs. 0.78), and ≥12 vs. <12 weeks (1.48 vs. 0.92). Amoderating effect of RT factors on muscle mass was not detected in YG, while greater ES was found in OG for RT with ≥3 vs. <3 days/week (0.50 vs. 0.25). Concluding, different combinations of RT factors improved strength and muscle mass in YG and OG. In OG, this was favoured by greater frequency and duration, although hampered by excessive volume.

Effects of intermittent fasting combined with resistance training on body composition: a systematic review and meta-analysis

This systematic review and meta-analysis evaluated the influence of intermittent fasting (IF) in combination with resistance training (RT) on body composition outcomes. Studies examining IF vs. non-IF diets in individuals performing RT, published up to February 2021, were identified through PubMed, the Cochrane Library, Web of Science, Embase, and SCOPUS databases. Eight studies, including 221 participants were analyzed using a random-effects model to calculate weighted mean differences (WMDs) with 95% confidence intervals (CIs). Results indicated that IF had a significant effect on body mass (WMD = -2.08 kg; 95% CI: -3.04, -1.13), fat mass (WMD = -1.36 kg; 95% CI: -1.94, -0.78), body mass index (WMD = -0.52 kg/m²; 95% CI: -0.85, -0.19), and body fat percentage (WMD = -1.49%; 95% CI: -2.24, -0.74) relative to non-IF diets, without a significant effect for fat-free mass (WMD = -0.27 kg; 95% CI: -0.82, 0.28). The present systematic review and meta-analysis demonstrates potentially beneficial effects of IF in combination with RT for reducing body mass and body fat relative to non-IF control diets, with similar preservation of fat-free mass.

Rehabilitation outcomes and parameters of blood flow restriction training in ACL injury: A scoping review

OBJECTIVE

To identify the outcomes of physical function, physical fitness, training, and cuff parameters, used in BFRT in ACL rehabilitation.

METHODS

This scoping review was initiated on April 25th, 2020, according to the PRISMA Extension for Scoping Reviews (PRISMA-ScR). Relevant literature was identified searching three main concepts: BFRT, rehabilitation and ACL injury on MEDLINE (PubMed), CENTRAL of Cochrane Library, Web of Science and PEDro. Studies looking at adults with a primary ACL injury undergoing conservative or pre/post-surgery rehabilitation with BFR or BFRT, with physical fitness and physical function as outcomes or other physical outcomes were included.

RESULTS

Sixty-eight articles were identified and six were included. One article was added through backward tracking. All studies used BFRT in the ACL injury surgical rehabilitation. Most studies evaluated physical fitness (muscular strength and volume) however, physical function was not considered a primary outcome. Training and cuff parameters were heterogeneously prescribed.

CONCLUSION

The existing evidence is not enough to draw definitive conclusions due to the heterogenous reported outcomes and parameters. Future investigation with standardized outcome measures and specific protocols are needed to draw conclusions on patients' physical function, so BFRT can be used more effectively in clinical rehabilitation practice.

Exercise-induced fluid shifts are distinct to exercise mode and intensity: a comparison of blood flow-restricted and free-flow resistance exercise

MRI can provide fundamental tools in decoding physiological stressors stimulated by training paradigms. Acute physiological changes induced by three diverse exercise protocols known to elicit similar levels of muscle hypertrophy were evaluated using muscle functional magnetic resonance imaging (mfMRI). The study was a cross-over study with participants (n = 10) performing three acute unilateral knee extensor exercise protocols to failure and a work matched control exercise protocol. Participants were scanned after each exercise protocol; 70% 1 repetition maximum (RM) (FF70); 20% 1RM (FF20); 20% 1RM with blood flow restriction (BFR20); free-flow (FF) control work matched to BFR20 (FF20_WM). Post exercise mfMRI scans were used to obtain interleaved measures of muscle R2 (indicator of edema), R2' (indicator of deoxyhemoglobin), muscle cross sectional area (CSA) blood flow, and diffusion. Both BFR20 and FF20 exercise resulted in a larger acute decrease in R2, decrease in R2', and expansion of the extracellular compartment with slower rates of recovery. BFR20 caused greater acute increases in muscle CSA than FF20_WM and FF70. Only BFR20 caused acute increases in intracellular volume. Postexercise muscle blood flow was higher after FF70 and FF20 exercise than BFR20. Acute changes in mean diffusivity were similar across all exercise protocols. This study was able to differentiate the acute physiological responses between anabolic exercise protocols. Low-load exercise protocols, known to have relatively higher energy contributions from glycolysis at task failure, elicited a higher mfMRI response. Noninvasive mfMRI represents a promising tool for decoding mechanisms of anabolic adaptation in muscle.NEW & NOTEWORTHY Using muscle functional MRI (mfMRI), this study was able to differentiate the acute physiological responses following three established hypertrophic resistance exercise strategies. Low-load exercise protocols performed to failure, with or without blood flow restriction, resulted in larger changes in R₂ (i.e. greater T₂-shifts) with a slow rate of return to baseline indicative of myocellular fluid shifts. These data were cross evaluated with interleaved measures of macrovascular blood flow, water diffusion, muscle cross sectional area (i.e. acute macroscopic muscle swelling), and intracellular water fraction measured using MRI.

Blood Flow Restriction Does Not Promote Additional Effects on Muscle Adaptations When Combined With High-Load Resistance Training Regardless of Blood Flow Restriction Protocol

ABSTRACT

Teixeira, EL, Ugrinowitsch, C, de Salles Painelli, V, Silva-Batista, C, Aihara, AY, Cardoso, FN, Roschel, H, and Tricoli, V. Blood flow restriction does not promote additional effects on muscle adaptations when combined with high-load resistance training regardless of blood flow restriction protocol. J Strength Cond Res 35(5): 1194-1200, 2021-The aim of this study was to investigate, during high-load resistance training (HL-RT), the effect of blood flow restriction (BFR) applied during rest intervals (BFR-I) and muscle contractions (BFR-C) compared with HL-RT alone (no BFR), on maximum voluntary isometric contraction (MVIC), maximum dynamic strength (one repetition maximum [1RM]), quadriceps cross-sectional area (QCSA), blood lactate concentration ([La]), and root mean square of the surface electromyography (RMS-EMG) responses. Forty-nine healthy and untrained men (25 ± 6.2 years, 178.1 ± 5.3 cm and 78.8 ± 11.6 kg) trained twice per week, for 8 weeks. One leg of each subject performed HL-RT without BFR (HL-RT), whereas the contralateral leg was randomly allocated to 1 of 2 unilateral knee extension protocols: BFR-I or BFR-C (for all protocols, 3 × 8 repetitions, 70% 1RM). Maximum voluntary isometric contraction, 1RM, QCSA, and acute changes in [La] and RMS-EMG were assessed before and after training. The measurement of [La] and RMS-EMG was performed during the control sessions with the same relative load obtained after the 1RM test, before and after training. Similar increases in MVIC, 1RM, and QCSA were demonstrated among all conditions, with no significant difference between them. [La] increased for all protocols in pre-training and post-training, but it was higher for BFR-I compared with the remaining protocols. Increases in RMS-EMG occurred for all protocols in pre-training and post-training, with no significant difference between them. In conclusion, despite of a greater metabolic stress, BFR inclusion to HL-RT during rest intervals or muscle contraction did not promote any additive effect on muscle strength and hypertrophy.

The effect of different resistance training protocols equalized by time under tension on the force-position relationship after 10 weeks of training period

This study investigated the impact of performing two equalized resistance training (RT) protocols for 10 weeks that differ only by repetition duration and number in the force-position and EMG-position relationship. Participants performed an equalized (36 s of time under tension; 3-4 sets; 3 min between sets; 50-55% of one-repetition maximum; 3× week) RT intervention on the bench press and the only different change between protocols was repetition number (RN; 12 vs.6) or duration (RD; 3 s vs. 6 s). Two experimental groups (RN₁₂RD₃, n = 12; and RN₆RD₆, n = 12) performed the RT, while one group was the control (Control, n = 11). Maximal isometric contractions at 10%, 50% and 90% of total bench press range of motion were performed pre- and post-RT, while electromyography was recorded. It demonstrated an increase in isometric force (+14% to 24%, P < 0.001) shifting up the force-position relationship of the training groups after RT, although no difference was between training groups compared to the Control. Neuromuscular activation from pectoralis major presented an increase after training for both RT groups (+44%; P < 0.001) compared to the Control. However, although not significantly different, triceps brachii also presented an increase depending on the protocol (+25%). In conclusion, 10 weeks of an equalized RT with longer RN and shorter RD (or opposite) similarly increases the ability to produce maximal isometric force during the bench exercise across different angles, while neuromuscular activation of the pectoralis major partially explained the shift-up of the force-position relationship after training.

Influence of resistance training load on measures of skeletal muscle hypertrophy and improvements in maximal strength and neuromuscular task performance: A systematic review and meta-analysis

This systematic review and meta-analysis determined resistance training (RT) load effects on various muscle hypertrophy, strength, and neuromuscular performance task [e.g., countermovement jump (CMJ)] outcomes. Relevent studies comparing higher-load [>60% 1-repetition maximum (RM) or <15-RM] and lower-load (≤60% 1-RM or ≥ 15-RM) RT were identified, with 45 studies (from 4713 total) included in the meta-analysis. Higher- and lower-load RT induced similar muscle hypertrophy at the whole-body (lean/fat-free mass; [ES (95% CI) = 0.05 (-0.20 to 0.29), P = 0.70]), whole-muscle [ES = 0.06 (-0.11 to 0.24), P = 0.47], and muscle fibre [ES = 0.29 (-0.09 to 0.66), P = 0.13] levels. Higher-load RT further improved 1-RM [ES = 0.34 (0.15 to 0.52), P = 0.0003] and isometric [ES = 0.41 (0.07 to 0.76), P = 0.02] strength. The superiority of higher-load RT on 1-RM strength was greater in younger [ES = 0.34 (0.12 to 0.55), P = 0.002] versus older [ES = 0.20 (-0.00 to 0.41), P = 0.05] participants. Higher- and lower-load RT therefore induce similar muscle hypertrophy (at multiple physiological levels), while higher-load RT elicits superior 1-RM and isometric strength. The influence of RT loads on neuromuscular task performance is however unclear.

Equating Resistance-Training Volume Between Programs Focused on Muscle Hypertrophy

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).

Combination of resistance and aerobic exercise for six months improves bone mass and physical function in HIV infected individuals: A randomized controlled trial

To evaluate the effect of combined resistance and aerobic training (RT+AT) on regional bone mineral density (BMD) and physical performance in people living with HIV (PLWH). Forty PLWH (20 men and 20 women) were randomized into RT+AT group (n = 20; age = 38.3 ± 4.9) or non-exercise control group (n = 20; age = 37.9 ± 5.1). The RT+AT group was required to perform a nonlinear periodized resistance training program targeting large muscle groups followed by 20 min aerobic exercise at 65-80% of maximal heart rate. Participants in RT+AT performed three supervised sessions per week for 6-months, whereas participants in the control group were instructed to continue with their current lifestyle habits. The primary outcome was bone mineral density (lumbar spine (L2-L4), femoral neck, and distal 1/3 radius). Secondary outcomes included physical function, anthropometry, inflammatory markers, and growth factors. The RT+AT group demonstrated a significant increase in BMD at follow-up for the Lumbar spine (L2-L4), femoral neck, and 1/3 radius (all, P < .05), and There were no gender differences in the training response between men and women for any of the BMD regions. Similar findings were also observed for lean body mass, IGF1and Adiponectin (P < .001). We observed a decrease in percent body fat, fat mass, IL-6, TNF-α, and myostatin in the RT+AT group (P < .001). Finally, there was a significant increase in handgrip strength and gait speed for both women and men in the RT+AT group (P < .001). A combination of resistance and aerobic training appears to be a feasible and effective means for counteracting bone loss and improving various inflammatory markers, physical function, and growth hormones in PLWH.

Resistance training with different repetition duration to failure: effect on hypertrophy, strength and muscle activation

Background

This study investigated the effects of two 14-week resistance training protocols with different repetition duration (RD) performed to muscle failure (MF) on gains in strength and muscle hypertrophy as well as on normalized electromyographic (EMG) amplitude and force-angle relationships.

Methods

The left and right legs of ten untrained males were assigned to either one of the two protocols (2-s or 6-s RD) incorporating unilateral knee extension exercise. Both protocols were performed with 3–4 sets, 50–60% of the one-repetition maximum (1RM), and 3 min rest. Rectus femoris and vastus lateralis cross-sectional areas (CSA), maximal voluntary isometric contraction (MVIC) at 30^o and 90^o of knee flexion and 1RM performance were assessed before and after the training period. In addition, normalized EMG amplitude-angle and force-angle relationships were assessed in the 6^th and 39^th experimental sessions.

Results

The 6-s RD protocol induced larger gains in MVIC at 30^o of knee angle measurement than the 2-s RD protocol. Increases in MVIC at 90^o of knee angle, 1RM, rectus femoris and vastus lateralis CSA were not significant between the 2-s and 6-s RD protocols. Moreover, different normalized EMG amplitude-angle and force-angle values were detected between protocols over most of the angles analyzed.

Conclusion

Performing longer RD could be a more appropriate strategy to provide greater gains in isometric maximal muscle strength at shortened knee positions. However, similar maximum dynamic strength and muscle hypertrophy gains would be provided by protocols with different RD.

Effects of resistance training combined with a ketogenic diet on body composition: a systematic review and meta-analysis

We evaluated the effects of ketogenic diets (KDs) on body mass (BM), fat mass (FM), fat-free mass (FFM), body mass index (BMI), and body fat percentage (BFP) compared to non-KDs in individuals performing resistance training (RT). Online electronic databases including PubMed, the Cochrane Library, Web of Science, Embase, SCOPUS, and Ovid were searched to identify initial studies until February 2021. Data were pooled using both fixed and random-effects methods and were expressed as weighted mean difference (WMD) and 95% confidence intervals (CI). Out of 1372 studies, 13 randomized controlled trials (RCTs) that enrolled 244 volunteers were included. The pooled results demonstrated that KDs significantly decreased BM [(WMD = -3.67 kg; 95% CI: -4.44, -2.90, p < 0.001)], FM [(WMD = -2.21 kg; 95% CI: -3.09, -1.34, p < 0.001)], FFM [(WMD = -1.26 kg; 95% CI: -1.82, -0.70, p < 0.001)], BMI [(WMD = -1.37 kg.m^-2; 95% CI: -2.14, -0.59, p = 0.022)], and BFP [(WMD = -2.27%; 95% CI: -3.63, -0.90, p = 0.001)] compared to non-KDs. We observed beneficial effects of KDs compared to non-KDs on BM and body fat (both FM and BFP) in individuals performing RT. However, adherence to KDs may have a negative effect on FFM, which is not ameliorated by the addition of RT.

Loading Recommendations for Muscle Strength, Hypertrophy, and Local Endurance: A Re-Examination of the Repetition Continuum

Loading recommendations for resistance training are typically prescribed along what has come to be known as the “repetition continuum”, which proposes that the number of repetitions performed at a given magnitude of load will result in specific adaptations. Specifically, the theory postulates that heavy load training optimizes increases maximal strength, moderate load training optimizes increases muscle hypertrophy, and low-load training optimizes increases local muscular endurance. However, despite the widespread acceptance of this theory, current research fails to support some of its underlying presumptions. Based on the emerging evidence, we propose a new paradigm whereby muscular adaptations can be obtained, and in some cases optimized, across a wide spectrum of loading zones. The nuances and implications of this paradigm are discussed herein.

Acute effects of muscle failure and training system (traditional vs. rest-pause) in resistance exercise on countermovement jump performance in trained adults

BACKGROUND: Traditional and rest-pause systems are commonly used during resistance training. These systems have different rest times between repetitions that might affect neuromuscular status and fatigue level. OBJECTIVE: This study compared the acute effects of traditional and rest-pause resistance exercise done to muscular failure on countermovement jump (CMJ) performance. METHODS: Twenty-nine recreationally strength-trained adults of both sexes aged from 18 to 33 years old performed four experimental resistance exercise sessions (half back-squat exercise) in a randomized order. The experimental conditions were: Traditional system to muscular failure (TR-F; 4 × 15 [15RM]) or non-failure (TR-NF; 5 × 12 [15RM]), and rest-pause system to muscular failure (RP-F; 60 reps with 30 s rest between each failure) or non-failure (RP-NF; 60 reps with 10.2 s rest between each repetition). CMJ height was measured at pre-experiment, Post-15 s, and Post-30 min. Perceived recovery was assessed at pre-experiment, lactate concentration Post-2 min, and rating of perceived exertion Post-30 min. RESULTS: CMJ height decrease occurred at Post-15 s and 30 min for the TR-F, TR-NF, and RP-F sessions (p< 0.05). Interaction effects (p< 0.05) showed exercise to muscle failure (TR-F and RP-F) induced greater neuromuscular decrement at Post-15 s, with RP-F leading to a higher CMJ performance impairment at Post-30 min (p< 0.001). Higher blood lactate concentrations were found following TR-F, TR-NF, and RP-F (p< 0.05) than RP-NF conditions, whereas greater internal training load perception was reported after training to muscular failure (p< 0.05) than non-failure exercise. CONCLUSION: Resistance exercise to muscular failure induced greater CMJ height decrement and internal training load perception than non-failure exercise, with RP-F leading to a higher acute neuromuscular performance impairment.

Strength Training: In Search of Optimal Strategies to Maximize Neuromuscular Performance

Training with low-load exercise performed under blood flow restriction can augment muscle hypertrophy and maximal strength to a similar extent as the classical high-load strength training method. However, the blood flow restriction method elicits only minor neural adaptations. In an attempt to maximize training-related gains, we propose using other protocols that combine high voluntary activation, mechanical tension, and metabolic stress.

Is stronger better? Influence of a strength phase followed by a hypertrophy phase on muscular adaptations in resistance-trained men

Although used by resistance-trained individuals, it is unknown if increasing muscle strength prior to hypertrophy training leads to greater muscle growth and strength gains. We investigated muscle thickness and maximum strength in 26 resistance-trained men who were randomly assigned to either: STHT, consisted in a 3-week strength-oriented training period (4x1-3 repetition maximum [RM]) prior to a 5-week hypertrophy-oriented period (4x8-12RM), or HT, which comprised an 8-week hypertrophy-oriented training period. Vastus lateralis muscle thickness, and back squat and leg-press 1-RM were assessed at pre, third week, and after 8 weeks of training. When pre-to-post changes are compared, STHT induced greater muscle growth (p = 0.049; 95%CI = 0.15-3.2%; d = 0.81) and strength gains in the back squat (p = 0.015; 95%CI = 1.5-13%; d = 1.05) and leg-press 45° (p = 0.044; 95%CI = 0.16-9.9%; d = 0.79) compared to HT. Our results support the use of a period to increase muscle strength prior to an HT to increase muscle thickness and maximum strength in resistance-trained men.

Varying the Order of Combinations of Single- and Multi-Joint Exercises Differentially Affects Resistance Training Adaptations

Brandão, L, de Salles Painelli, V, Lasevicius, T, Silva-Batista, C, Brendon, H, Schoenfeld, BJ, Aihara, AY, Cardoso, FN, de Almeida Peres, B, and Teixeira, EL. Varying the order of combinations of single- and multi-joint exercises differentially affects resistance training adaptations. J Strength Cond Res 34(5): 1254-1263, 2020-Our study aimed to compare the effects of multi-joint (MJ) and single-joint (SJ) exercises, either isolated or in combination, and in different orders, on cross-sectional area (CSA) of the pectoralis major (PM) and different heads of the triceps brachii (TB), as well as on the one-repetition maximum (1-RM) in the bench press and lying barbell triceps press. Forty-three young men were randomly assigned to one of 4 possible RT protocols: barbell bench press plus lying barbell triceps press (MJ + SJ, n = 12); lying barbell triceps press plus barbell bench press (SJ + MJ, n = 10); barbell bench press (MJ, n = 10); or lying barbell triceps press (SJ, n = 11). Results showed significant within-group increases in 1-RM bench press for MJ, MJ + SJ, and SJ + MJ but not for SJ. Conversely, significantly greater within-group increases in elbow extension 1-RM were noted for SJ, MJ + SJ, and SJ + MJ but not for MJ. Significantly greater increases in PM CSA were observed for MJ, MJ + SJ, and SJ + MJ compared with SJ. Significant increases in TB CSA were noted for SJ, MJ + SJ, and SJ + MJ, but not for MJ, without observed between-group differences. Individual analysis of TB heads showed significantly greater CSA increases in the lateral head for MJ, MJ + SJ, and SJ + MJ compared with SJ. Alternatively, significantly greater increases in the long head were observed for SJ, MJ + SJ, and SJ + MJ compared with MJ. CSA increases for the medial head were statistically similar between conditions. Our findings indicate that muscular adaptations are differentially affected by performance of MJ and SJ exercises.

Strength testing or strength training: considerations for future research

Maximal strength testing is often performed to assess the efficacy of training programs or as a way to prescribe exercise load. Generally, it is believed that high load exercise is superior to low load exercise at increasing absolute strength, however this is not always the case (i.e. strength increases similarly between groups). We hypothesized that some of the discrepancy in the literature may be related to performing the strength test itself. To investigate this further we reviewed the literature looking for studies comparing high load and low load exercise. The included studies were separated into 'no extra practice' and 'practice'. No extra practice means the strength test was only performed at pre and post whereas practice refers to additional strength tests performed throughout the training intervention. Our results indicated that the differences between high load and low load exercise can be reduced when the group training with a low load is allowed additional exposure to the maximal strength test. This suggests that repeated exposure to strength tests may augment low load training adaptations and influence the outcomes. We discuss potential moderators of this relationship (e.g. how low is the low load, complexity of the skill) and offer considerations for future research. Based on this it would be recommended that when investigating the effects of low load training strength tests should be limited to pre and post intervention or if a control group is utilized then the control group should receive the same number of exposures to the strength test.

High intensity training during spaceflight: results from the NASA Sprint Study

Historically, International Space Station (ISS) exercise countermeasures have not fully protected astronauts’ musculoskeletal and cardiorespiratory fitness. Although these losses have been reduced on more recent missions, decreasing the time required to perform in-flight exercise would permit reallocation of that time to other tasks. To evaluate the effectiveness of a new training prescription, ISS crewmembers performed either the high intensity/lower volume integrated Sprint resistance (3 d wk⁻¹) and aerobic (interval and continuous workouts, each 3 d wk⁻¹ in alternating fashion) exercise program (n = 9: 8M/1F, 48 ± 7 y, 178 ± 5 cm, 77.7 ± 12.0 kg) or the standard ISS countermeasure consisting of daily resistance and aerobic exercise (n = 17: 14M/3F, 46 ± 6 y, 176 ± 6 cm, 80.6 ± 10.5 kg) during long-duration spaceflight. Bone mineral density (dual energy X-ray absorptiometry (DXA)), muscle strength (isokinetic dynamometry), muscle function (cone agility test), and cardiorespiratory fitness (VO_2peak) were assessed pre- and postflight. Mixed-effects modeling was used to analyze dependent measures with alpha set at P < 0.05. After spaceflight, femoral neck bone mineral density (−1.7%), knee extensor peak torque (−5.8%), cone agility test time (+7.4%), and VO_2peak (−6.1%) were decreased in both groups (simple main effects of time, all P < 0.05) with a few group × time interaction effects detected for which Sprint experienced either attenuated or no loss compared to control. Although physiologic outcomes were not appreciably different between the two exercise programs, to conserve time and optimally prepare crewmembers for the performance of physically demanding mission tasks, high intensity/lower volume training should be an indispensable component of spaceflight exercise countermeasure prescriptions.

Feasibility of eccentric overloading and neuromuscular electrical stimulation to improve muscle strength and muscle mass after treatment for head and neck cancer

PURPOSE

Treatment of head and neck cancer (HNC) results in severe weight loss, mainly due to the loss of lean body mass. Consequently, decreases in muscular strength and health-related quality of life (HRQL) occur. This study investigated the feasibility of a 12-week novel strength training (NST) and conventional strength training (CST) intervention delivered after HNC treatment.

METHODS

Participants were randomized to a NST group (n = 11) involving eccentric overloaded strength training and neuromuscular electrical stimulation (NMES), or a CST group (n = 11) involving dynamic resistance exercises matched for training volume. Feasibility outcomes included recruitment, completion, adherence, and evidence of progression. A neuromuscular assessment involving maximal isometric voluntary contractions (MIVCs) in the knee extensors was evaluated prior to and during incremental cycling to volitional exhaustion at baseline and after the interventions. Anthropometrics and patient-reported outcomes (PROs) were also assessed.

RESULTS

Although recruitment was challenging, completion was 100% in NST and 82% in CST. Adherence was 92% in NST and 81% in CST. Overall, MIVC increased by 19 ± 23%, muscle cross-sectional area improved 18 ± 22%, cycling exercise time improved by 18 ± 13%, and improvements in HRQL and fatigue were clinically relevant.

CONCLUSIONS

Both interventions were found to be feasible for HNC patients after treatment. Strength training significantly improved maximal muscle strength, muscle cross-sectional area, and PROs after HNC treatment. Future research should include fully powered trials and consider the use of eccentric overloading and NMES during HNC treatment.

IMPLICATIONS FOR CANCER SURVIVORS

Eccentric- and NMES-emphasized strength training may be useful alternatives to conventional strength training after HNC treatment.

Session Rating of Perceived Exertion as an Efficient Tool for Individualized Resistance Training Progression

Gomes, RL, Lixandrão, ME, Ugrinowitsch, C, Moreira, A, Tricoli, V, and Roschel, H. Session rating of perceived exertion as an efficient tool for individualized resistance training progression. J Strength Cond Res XX(X): 000-000, 2020-The present study aimed to investigate the effects of an individualized resistance training (RT) progression model based on the session rating of perceived exertion (RPE) on gains in muscle mass and strength when compared with a conventional predetermined progression method (PP). Twenty previously trained young male subjects were randomly allocated to 1 of the 2 groups: RPE (n = 10) or PP (n = 10). Muscle cross-sectional area (CSA) and maximum dynamic strength were assessed at baseline and after 6 weeks. The RPE-based progression model resulted in a lower number of high-intensity sessions compared with the PP-based model. Despite this, both groups showed significant and similar increases in CSA (p < 0.0001; RPE = 6.55 ± 5.27% and PP = 9.65 ± 3.63%) and strength (p < 0.0001; RPE = 9.68 ± 4.57% and PP = 9.28 ± 4.01%) after the intervention period. No significant between-group difference was observed for total training volume (RPE = 45,366.00 ± 10,190.00 kg and PP = 47,779.00 ± 5,685.00 kg; p = 0.52). Our results showed that an RT progression model based on session-to-session physiological response assessments resulted in fewer high-intensity training sessions while allowing for similar gains in muscle strength and mass. Thus, trainees are encouraged to adopt session RPE as a potential tool to control workload progression throughout a training period and allowing the optimization of training stimulus on an individual basis.

Effects of resistance training with controlled versus self-selected repetition duration on muscle mass and strength in untrained men

The aim of this study was to compare the effect of self-selected repetition duration (SELF), with and without volume load (VL) equalized with controlled repetition duration (CON) on muscle strength and hypertrophy in untrained males. We used a within-subjects design in which 20 volunteers (age: 24.7 ± 2.9 years) had one leg randomly assigned to CON (i.e., 2 s concentric, 2 s eccentric) and the other to SELF or to self-selected repetition duration with equalized volume load (SELF-EV). One repetition maximum (1-RM) and muscle cross-sectional area (CSA) were measured at baseline (Pre) and after (Post) resistance training (RT; 2×/wk for 8 weeks). For the main study variables (1-RM and muscle CSA), a mixed-model analysis was performed, assuming repetition duration (SELF, SELF-EV and CON), and time (Pre and Post) as fixed factors and the subjects as random factor for each dependent variable (1-RM and CSA). All RT protocols showed significant increases in values of 1-RM from Pre (CON: 73.7 ± 17.6 kg; SELF: 75.9 ± 17.7 kg; and SELF-EV: 72.6 ± 16.9 kg) to Post (CON: 83.4 ± 19.9 kg, effect size (ES): 0.47; SELF: 84 ± 19.1 kg, ES: 0.43; and SELF-EV: 83.2 ± 19.9 kg, ES: 0.57, P < 0.0001). Muscle CSA values increased for all protocols from Pre (CON: 12.09 ± 3.14 cm²; SELF: 11.91 ± 3.71 cm²; and SELF-EV: 11.93 ± 2.32 cm²) to Post (CON: 13.03 ± 3.25 cm², ES: 0.29; SELF: 13.2 ± 4.16 cm², ES: 0.32; and SELF-EV: 13.2 ± 2.35 cm², ES: 0.53, P < 0.0001). No significant differences between protocols were found for both 1-RM and CSA (P > 0.05). Performing RT with SELF, regardless of VL, was equally effective in inducing increases in muscle strength and hypertrophy compared to CON in untrained men.

Muscle thickness and strength adaptations in dominant and non-dominant upper limbs

BACKGROUND

It is currently unknown if muscle growth and strength gain are similar in both dominant and non-dominant limbs of the same individual with the same training load. Therefore, the objective of this study was to analyze initial muscle size and strength levels in both upper limbs and compare changes in muscle size and strength between dominant and non-dominant upper limbs with a within-individual experimental design with high-load resistance training.

METHODS

Ten untrained participants performed six weeks of unilateral resistance training for upper limbs (i.e., elbow flexors) using 80% of 1 repetition maximum (1RM). Muscle thickness and 1RM were assessed before and after the training period. We used a two-way repeated measures ANOVA to compared changes between limbs, effect sizes (ES) were also calculated.

RESULTS

Muscle thickness and 1RM were not different between limbs at baseline. There was a main time effect for muscle thickness (P<0.0001; dominant: 10±4%, ES=0.83; non-dominant: 11±3%, ES=0.85) and 1RM (P<0.0001; dominant: 23±15%, ES=1.8; non-dominant: 30±17%, ES=1.9), but there was no interaction effect for muscle thickness (P=0.63) and 1RM (P=0.32). There was no difference between dominant and non-dominant limbs in volume load (ES=0.4; P=0.13).

CONCLUSIONS

Similar baseline strength level and muscle thickness, and training volume may explain similar adaptations observed. Within-individual design seems reliable to investigate training models as both limbs adapt similarly to the same stimulus.

Scientific Basis for Eccentric Quasi-Isometric Resistance Training: A Narrative Review

Oranchuk, DJ, Storey, AG, Nelson, AR, and Cronin, JB. The scientific basis for eccentric quasi-isometric resistance training: A narrative review. J Strength Cond Res 33(10): 2846-2859, 2019-Eccentric quasi-isometric (EQI) resistance training involves holding a submaximal, yielding isometric contraction until fatigue causes muscle lengthening and then maximally resisting through a range of motion. Practitioners contend that EQI contractions are a powerful tool for the development of several physical qualities important to health and sports performance. In addition, several sports involve regular quasi-isometric contractions for optimal performance. Therefore, the primary objective of this review was to synthesize and critically analyze relevant biological, physiological, and biomechanical research and develop a rationale for the value of EQI training. In addition, this review offers potential practical applications and highlights future areas of research. Although there is a paucity of research investigating EQIs, the literature on responses to traditional contraction types is vast. Based on the relevant literature, EQIs may provide a practical means of increasing total volume, metabolite build-up, and hormonal signaling factors while safely enduring large quantities of mechanical tension with low levels of peak torque. Conversely, EQI contractions likely hold little neuromuscular specificity to high velocity or power movements. Therefore, EQI training seems to be effective for improving musculotendinous morphological and performance variables with low injury risk. Although speculative due to the limited specific literature, available evidence suggests a case for future experimentation.

Type of Exercise Training and Training Methods

There is general agreement that exercise training leads to functional, morphological, and metabolic adaptations of different biological systems, thereby increasing overall physical performance and promoting good health. Thus, an active lifestyle is propagated in all age groups. However, not every exercise routine or workout is suitable for everyone. Inappropriate training can also pose risks, and too low or too high training intensity or volume often does not lead to the expected success. To ensure significant benefits, specific principles and strategies need to be considered and accustomed to the individual.This chapter summarizes the key exercise variables and training principles to consider when developing a training program to improve or maintain performance and health. In addition, the various steps for creating an individual training program are described, and an overview of the different training methods and training strategies is given.

The Effects of Increasing Training Load on Affect and Perceived Exertion

Cavarretta, DJ, Hall, EE, and Bixby, WR. The effects of increasing training load on affect and perceived exertion. J Strength Cond Res XX(X): 000-000, 2019-This study was designed to investigate how affect and ratings of perceived exertion based on repetitions in reserve (RPE/RIR) change as a function of increasing load during a 10 repetition maximum (RM) test. Twenty-nine novice lifters completed a 10RM test for 2 different conditions presented in a randomized, counterbalanced fashion. RPE/RIR and affect were assessed immediately after each successful 10RM attempt. RPE/RIR was significantly different at all loads from 50 to 100% 10RM (p < 0.001) with no differences between exercise and exercise load (p = 0.059). RPE/RIR was higher for all lower body exercises compared with upper-body exercises (p < 0.001) but was not different between machine and free-weight exercises (p > 0.344). Affect became less positive only at 100% 10RM compared with all other loads (p < 0.05). Finally, affect was more positive for upper-body exercises compared to lower-body exercises (p = 0.025) and more positive for machines compared to free-weights (p = 0.015). The results of this study suggest that among novice lifters, RPE/RIR increases as load increases during a 10RM and affective valence remains relatively constant but becomes less positive when exercising at maximal intensities (100% 10RM). Further research is needed to replicate these findings and elucidate the effects of different muscles used (e.g., upper vs. lower body) and modality of exercise (e.g., machine vs. free-weight) on RPE/RIR and affect among both novice and experienced lifters.

Maximizing Muscle Hypertrophy: A Systematic Review of Advanced Resistance Training Techniques and Methods

BACKGROUND

Effective hypertrophy-oriented resistance training (RT) should comprise a combination of mechanical tension and metabolic stress. Regarding training variables, the most effective values are widely described in the literature. However, there is still a lack of consensus regarding the efficiency of advanced RT techniques and methods in comparison to traditional approaches.

METHODS

MEDLINE and SPORTDiscus databases were searched from 1996 to September 2019 for all studies investigating the effects of advanced RT techniques and methods on muscle hypertrophy and training variables. Thirty articles met the inclusion criteria and were consequently included for the quality assessment and data extraction.

RESULTS

Concerning the time-efficiency of training, the use of agonist-antagonist, upper-lower body supersets, drop and cluster sets, sarcoplasma stimulating training, employment of fast, but controlled duration of eccentric contractions (~2s), and high-load RT supplemented with low-load RT under blood flow restriction may provide an additional stimulus and an advantage to traditional training protocols. With regard to the higher degree of mechanical tension, the use of accentuated eccentric loading in RT should be considered. Implementation of drop sets, sarcoplasma stimulating training, low-load RT in conjunction with low-load RT under blood flow restriction could provide time-efficient solutions to increased metabolic stress.

CONCLUSIONS

Due to insufficient evidence, it is difficult to provide specific guidelines for volume, intensity of effort, and frequency of previously mentioned RT techniques and methods. However, well-trained athletes may integrate advanced RT techniques and methods into their routines as an additional stimulus to break through plateaus and to prevent training monotony.

Effects of Pre-exhaustion Versus Traditional Resistance Training on Training Volume, Maximal Strength, and Quadriceps Hypertrophy

BACKGROUND

The pre-exhaustion (PreEx) method is used as a resistance training (RT) method to increase muscle mass, yet the chronic effects of this method are poorly understood.

OBJECTIVE

Although readily prescribed as a RT method for promotion of muscle hypertrophy, few researches give light to gains made after chronic PreEx RT. Therefore, we compared the effects of traditional versus PreEx RT programs on muscle strength, body composition, and muscular hypertrophy in adult males.

METHODS

Untrained subjects (age: 31.37 ± 6.83 years; height: 175.29 ± 5.52 cm; body mass: 82.04 ± 13.61 kg; 1RM leg press: 339.86 ± 61.17 kg; 1RM leg extension: 121.71 ± 11.93 kg) were submitted to 9 weeks of RT with weekly sessions. Traditional (TRT) group (n = 12) performed three sets at 45° of leg press exercise at 75% of 1RM, PreEx group (n = 12) completed a set to failure on a leg extension machine prior to the leg press, and the control (CON) group (n = 7) did not train. Maximum strength, muscle thickness, and body composition were analyzed.

RESULTS

PreEx group increased in maximal strength on leg press (16 ± 8%) and leg extension (17 ± 11%), while the TRT group improved by 15 ± 9 and 11 ± 4%, respectively. The thickness of the quadriceps muscles increased for both intervention groups. Specifically, the post-training thickness of the vastus lateralis was significantly higher for PreEx (55%) compared to the CON group. The TRT group presented a greater loss of total and thigh fat mass when compared with the PreEx method. These results were found in the presence of a lower training load for the PreEx group.

CONCLUSION

The PreEx training can decrease the total training volume while maintaining results in strength and hypertrophy when comparing to TRT. However, TRT may be optimal if the goal is to decrease fat mass.

Supervised Physical Training Enhances Muscle Strength but Not Muscle Mass in Prostate Cancer Patients Undergoing Androgen Deprivation Therapy: A Systematic Review and Meta-Analysis

Introduction: Androgen deprivation therapy (ADT) is considered the basic treatment for advanced prostate cancer, but it is highly associated with detrimental changes in muscle mass and muscle strength. The aim of this meta-analysis was to investigate the effects of supervised physical training on lean mass and muscle strength in prostate cancer patients undergoing ADT.

Methods: A systematic literature search was performed using MEDLINE, Embase, and ScienceDirect until October 2018. Only studies that examined both muscle mass and strength in prostate cancer patients undergoing ADT were included. Outcomes of interest were changes in lean body mass (surrogate for muscle mass) as well as upper and lower body muscle strength. The meta-analysis was performed with fixed-effects models to calculate mean differences between intervention and no-training control groups.

Results: We identified 8,521 publications through the search of the following key words: prostate cancer, prostate tumor, prostate carcinoma, prostate neoplasm, exercise, and training. Out of these studies, seven randomized controlled trials met the inclusion criteria and where included in the analysis. No significant mean differences for changes in lean mass were observed between the intervention and control groups (0.49 kg, 95% CI: −0.76, 1.74; P = 0.44). In contrast, the mean difference for muscle strength was significant both in chest (3.15 kg, 95% CI: 2.46, 3.83; P < 0.001) and in leg press (27.46 kg, 95% CI: 15.05, 39.87; p < 0.001).

Conclusion: This meta-analysis provides evidence that low- to moderate-intensity resistance and aerobic training is effective for increasing muscle strength but may not be sufficient to affect muscle mass in prostate cancer patients undergoing ADT. The underlying mechanisms for this maladaptation may in part be explained by an insufficient stimulus induced by the training regimens as well as a delayed initiation of training in relation to the start of ADT. When interpreting the present findings, one should bear in mind that the overall number of studies included in this review was rather low, emphasizing the need for further studies in this field.

Effect of individualized resistance training prescription with heart rate variability on individual muscle hypertrophy and strength responses

The aim of the present study was to investigate if resistance training (RT), performed with individualized recovery between sessions (RT-IND), promotes greater gains in strength and muscle mass and reduces the variability on adaptations compared to RT with fixed recovery intervals (RT-FIX). Twenty young men (age 21.9 ± 3.3 years) were randomized in the RT-IND and RT-FIX groups. Five days before the beginning of the training, measurements of the root mean square of successive R-R intervals differences (RMSSD) values of each individual were performed to establish the baseline values. Before each RT session, the RMSSD values determined whether the participants from RT-IND protocol were recovered from the previous session. Participants performed the RT session only if RMSSD values had returned to the baseline, otherwise they had to wait for an additional 24 h. RT-FIX performed an RT session every 48 h. Muscle strength was measured by one-maximal repetition (1-RM) test and muscle cross-section area (CSA) of the vastus laterals by ultrasonography were assessed pre- and post-training. 1-RM values increased significantly from pre to post-training for both groups (RT-IND: 30% and RT-FIX: 42%, main time effect, P < 0001), with no significant difference between groups. Muscle CSA increased significantly from pre to post-training (RT-IND: 15.7% and RT-FIX: 15.8%, main time effect, P < 0001), with no significant difference between groups. In conclusion, RT-IND did not increase the gains in muscle strength and mass neither reduce the variability in muscle adaptations when compared to the RT-FIX.

Stimuli and sensors that initiate skeletal muscle hypertrophy following resistance exercise

One of the most striking adaptations to exercise is the skeletal muscle hypertrophy that occurs in response to resistance exercise. A large body of work shows that a mammalian target of rapamycin complex 1 (mTORC1)-mediated increase of muscle protein synthesis is the key, but not sole, mechanism by which resistance exercise causes muscle hypertrophy. While much of the hypertrophy signaling cascade has been identified, the initiating, resistance exercise-induced and hypertrophy-stimulating stimuli have remained elusive. For the purpose of this review, we define an initiating, resistance exercise-induced and hypertrophy-stimulating signal as "hypertrophy stimulus," and the sensor of such a signal as "hypertrophy sensor." In this review we discuss our current knowledge of specific mechanical stimuli, damage/injury-associated and metabolic stress-associated triggers, as potential hypertrophy stimuli. Mechanical signals are the prime hypertrophy stimuli candidates, and a filamin-C-BAG3-dependent regulation of mTORC1, Hippo, and autophagy signaling is a plausible albeit still incompletely characterized hypertrophy sensor. Other candidate mechanosensing mechanisms are nuclear deformation-initiated signaling or several mechanisms related to costameres, which are the functional equivalents of focal adhesions in other cells. While exercise-induced muscle damage is probably not essential for hypertrophy, it is still unclear whether and how such muscle damage could augment a hypertrophic response. Interventions that combine blood flow restriction and especially low load resistance exercise suggest that resistance exercise-regulated metabolites could be hypertrophy stimuli, but this is based on indirect evidence and metabolite candidates are poorly characterized.

Muscle Adaptations to High-Load Training and Very Low-Load Training With and Without Blood Flow Restriction

An inability to lift loads great enough to disrupt muscular blood flow may impair the ability to fatigue muscles, compromising the hypertrophic response. It is unknown what level of blood flow restriction (BFR) pressure, if any, is necessary to reach failure at very low-loads [i.e., 15% one-repetition maximum (1RM)]. The purpose of this study was to investigate muscular adaptations following resistance training with a very low-load alone (15/0), with moderate BFR (15/40), or with high BFR (15/80), and compare them to traditional high-load (70/0) resistance training. Using a within/between subject design, healthy young participants (n = 40) performed four sets of unilateral knee extension to failure (up to 90 repetitions/set), twice per week for 8 weeks. Data presented as mean change (95% CI). There was a condition by time interaction for 1RM (p < 0.001), which increased for 70/0 [3.15 (2.04,4.25) kg] only. A condition by time interaction (p = 0.028) revealed greater changes in endurance for 15/80 [6 (4,8) repetitions] compared to 15/0 [4 (2,6) repetitions] and 70/0 [4 (2,5) repetitions]. There was a main effect of time for isometric MVC [change = 10.51 (3.87,17.16) Nm, p = 0.002] and isokinetic MVC at 180^°/s [change = 8.61 (5.54,11.68) Nm, p < 0.001], however there was no change in isokinetic MVC at 60^°/s [2.45 (−1.84,6.74) Nm, p = 0.261]. Anterior and lateral muscle thickness was assessed at 30, 40, 50, and 60% of the upper leg. There was no condition by time interaction for muscle thickness sites (all p ≥ 0.313). There was a main effect of time for all sites, with increases over time (all p < 0.001). With the exception of the 30% lateral site (p = 0.059) there was also a main effect of condition (all p < 0.001). Generally, 70/0 was greater. Average weekly volume increased for all conditions across the 8 weeks, and was greatest for 70/0 followed by 15/0, 15/40, then 15/80. With the exception of 1RM, changes in strength and muscle size were similar regardless of load or restriction. The workload required to elicit these changes lowered with increased BFR pressure. These findings may be pertinent to rehabilitative settings, future research, and program design.