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Purpose: Neuromuscular deficits and atrophy after anterior cruciate ligament reconstruction (ACLR) may be accompanied by changes in muscle composition and poor quadriceps muscle quality (QMQ). Quadriceps atrophy occurs after ACLR but improves within the first three postoperative months, yet this hypertrophy could be attributable to increases in noncontractile tissue (i.e., poor QMQ). The purposes of this study were to evaluate changes in QMQ after ACLR and to determine if changes in QMQ and cross-sectional area (CSA) occur in parallel or independently. Methods: A longitudinal prospective cohort design was implemented to evaluate QMQ and CSA in 20 individuals with ACLR and 12 healthy controls. Participants completed three testing sessions (baseline/presurgery, 1 month, and 3 months) during which ultrasound images were obtained from the vastus lateralis (VL) and rectus femoris (RF). QMQ was calculated as the echo intensity (EI) of each image, with high EI representing poorer QMQ. Anatomical CSA was also obtained from each image. Results: RF and VL EI were greater at 1 and 3 months in the ACLR limb compared with baseline and the contralateral limb and did not change between 1 and 3 months. VL and RF CSA in the ACLR limb were smaller at 1 and 3 months compared with the contralateral limb and controls (VL only) but increased from 1 to 3 months. Changes in QMQ and CSA were not correlated. Conclusions: QMQ declines within the first month after ACLR and does not improve by 3 months although hypertrophy occurs, suggesting that these morphological characteristics change independently after ACLR. Poorer QMQ represents greater concentration of noncontractile tissues within the muscle and potentially contributes to chronic quadriceps dysfunction observed after ACLR. [ABSTRACT FROM AUTHOR]

Purpose: This study investigated the effect of progressively adding sets for the lower limb every 2 wk versus performing a constant set volume in resistance-trained males. Methods: Thirty-one resistance-trained males (age = 24.4 ± 2.9 yr, height = 175.5 ± 6.5 cm, body mass = 80.1 ± 9.4 kg, body fat = 14.4% ± 3.1%, resistance training [RT] experience = 5.1 ± 2.2 yr; one-repetition maximum [1RM] barbell back squat: body mass ratio = 1.7 ± 0.1 a.u.) were randomly allocated into a constant group (CG, n = 10), a four-set progression group (4SG, n = 10) or a six-set progression group (6SG, n = 11). After a 2-wk washout period and another 2-wk familiarization period, participants performed a lower-limb training program twice a week for 12 wk. Maximum dynamic strength (1RM) in the barbell back squat, vastus lateralis cross-sectional area, and the sum of lateral thigh muscle thickness at 30%, 50%, and 70% of the femur length were assessed at baseline and after the 12-wk training program. Results: Regarding 1RM, multiple comparisons revealed that 6SG elicited higher muscle strength gains than 4SG (P = 0.002) and CG (P < 0.0001), and 4SG had greater improvements than CG (P = 0.023). Cross-sectional area and sum of lateral thigh muscle thickness showed no between-group differences (P = 0.067 and P = 0.076, respectively). However, an inspection of 95% confidence intervals suggests a potential dose–response relationship, with results appearing to plateau in the higher volume conditions. Conclusions: Our results suggest that progressively adding four or six sets per week every 2 wk elicited greater lower-limb strength in resistance-trained individuals over a 12-wk training period. Although our findings indicate a possible small benefit for higher volume conditions regarding hypertrophic adaptations in this population, the limited certainty of our findings warrants caution. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to compare the effects of free-weight andmachine-based resistance training on strength, hypertrophy, and joint discomfort. Methods: Thirty-eight resistance-trained men participated in an 8-wk resistance program allocated into free-weight (n = 19) or machine-based (n = 19) groups. Training variables were identical for both modalities, so they only differed in the use of barbells or machines to execute the full squat, bench press, prone bench pull, and shoulder press exercises. The velocity-based method was implemented to accurately adjust the intensity throughout the program. Strength changes were evaluated using eight velocity-monitored loading tests (four exercises two modalities) and included the relative one-repetition maximum (1RMRel), as well as the mean propulsive velocity against low (MPVLow) and high (MPVHigh) loads. Ultrasound-derived cross-sectional area of quadriceps (proximal and distal regions), pectoralis major, and rectus abdominis was measured to examine hypertrophy. Complementarily, Western Ontario and McMaster Universities and Disabilities of the Arm, Shoulder and Hand questionnaires were administrated to assess changes in lower- and upper-limb joint discomfort. Outcomes were compared using ANCOVA and percentage of change (Δ) statistics. Results: Each group significantly ( P < 0.001) increased 1RMRel, MPVLow, and MPVHigh for both modalities tested, but especially in the one they trained.When considering together the eight exercises tested, strength changes for both modalities were similar (Δ differences ≤1.8%, P ≥ 0.216). Likewise, the cross-sectional area of all the muscles evaluated was significantly increased by both modalities, with no significant differences between them (Δ difference ≤2.0%, P ≥ 0.208). No between-group differences ( P ≥ 0.144) were found for changes in stiffness, pain, and functional disability levels, which were reduced by both modalities. Conclusions: Free-weight and machine-based modalities are similarly effective to promote strength and hypertrophy without increasing joint discomfort. [ABSTRACT FROM AUTHOR]

Introduction: Athletes use their skeletal muscles to demonstrate performance. Muscle force generating capacity is correlated with volume, meaning that variations in sizes of different muscles may be indicative of how athletes meet different demands in their sports. Medical imaging enables in vivo quantification ofmuscle volumes; however, muscle volume distribution has not been compared across athletes of different sports. Purpose: The goal of this work was to define "muscular phenotypes" in athletes of different sports and compare these using hierarchical clustering. Methods: Muscle volumes normalized by body mass of athletes (football, baseball, basketball, or track) were compared with control participants to quantify size differences using z-scores. z-Scores of 35 muscles described the pattern of volume deviation within each athlete's lower limb, characterizing their muscular phenotype. Data-driven high-dimensional clustering analysis was used to group athletes presenting similar phenotypes. Efficacy of clustering to identify similar phenotypes was demonstrated by grouping athletes' contralateral limbs before other athletes' limbs. Results: Analyses revealed that athletes did not tend to cluster with others competing in the same sport. Basketball players with similar phenotypes grouped by clustering also demonstrated similarities in performance. Clustering also identified muscles with similar volume variation patterns across athletes, and principal component analysis revealed specific muscles that accounted for most of the variance (gluteus maximus, sartorius, semitendinosus, vastus medialis, vastus lateralis, and rectus femoris). Conclusions: Athletes exhibit heterogeneous lower limb muscle volumes that can be characterized and compared as individual muscular phenotypes. Clustering revealed that athletes with the most similar phenotypes do not always play the same sport such that patterns of muscular heterogeneity across a group of athletes reflect factors beyond their specific sports. [ABSTRACT FROM AUTHOR]

Purpose: The optimal intensity of resistance training (RT) to improve muscular, physical performance, and metabolic adaptations still needs to be well established for older adults. Based on current position statements, we compared the effects of two different RT loads on muscular strength, functional performance, skeletal muscle mass, hydration status, and metabolic biomarkers in older women. Methods: One hundred one older women were randomly allocated to perform a 12-wk whole-body RT program (eight exercises, three sets, three nonconsecutive days a week) into two groups: 8-12 repetitions maximum (RM) and 10-15RM. Muscular strength (1RM tests), physical performance (motor tests), skeletal muscle mass (dual-energy X-ray absorptiometry), hydration status (bioelectrical impedance), and metabolic biomarkers (glucose, total cholesterol, HDL-c, HDL-c, triglycerides, and C-reactive protein) were measured at baseline and posttraining. Results: Regarding muscular strength, 8-12RM promoted higher 1RM increases in chest press (+23.2% vs +10.7%, P < 0.01) and preacher curl (+15.7% vs +7.4%, P < 0.01), but not in leg extension (+14.9% vs +12.3%, P > 0.05). Both groups improved functional performance (P <0.05) in gait speed (4.6%-5.6%), 30 s chair stand (4.6%-5.9%), and 6 min walking (6.7%-7.0%) tests, with no between-group differences (P > 0.05). The 10-15RM group elicited superior improves in the hydration status (total body water, intracellular and extracellular water; P < 0.01), and higher gains of skeletal muscle mass (2.5% vs 6.3%, P < 0.01), upper (3.9% vs 9.0%, P < 0.01) and lower limbs lean soft tissue (2.1% vs 5.4%, P < 0.01). Both groups improved their metabolic profile. However, 10-15RM elicited greater glucose reductions (-0.2% vs -4.9%, P < 0.05) and greater HDL-c increases (-0.2% vs +4.7%, P < 0.01), with no between-group differences for the other metabolic bio-markers (P > 0.05). Conclusions: Our results suggest that 8-2RM seems more effective than 10-15RM for increasing upper limbs' muscular strength, whereas the adaptative responses for lower limbs and functional performance appear similar in older women. In contrast, 10-15RM seems more effective for skeletal muscle mass gains, and increased intracellular hydration and improvements in metabolic profile may accompany this adaptation. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to compare and rank gluteal muscle forces in eight hip-focused exercises performed with and without external resistance and describe the underlying fiber lengths, velocities, and muscle activations. Methods: Motion capture, ground reaction forces, and electromyography (EMG) were used as input to an EMG-informed neuromusculoskeletal model to estimate gluteus maximus, medius, and minimus muscle forces. Participants were 14 female footballers (18–32 yr old) with at least 3 months of lower limb strength training experience. Each participant performed eight hip-focused exercises (single-leg squat, split squat, single-leg Romanian deadlift [RDL], single-leg hip thrust, banded side step, hip hike, side plank, and side-lying leg raise) with and without 12 repetition maximum (RM) resistance. For each muscle, exercises were ranked by peak muscle force, and k-means clustering separated exercises into four tiers. Results: The tier 1 exercises for gluteus maximus were loaded split squat (95% confidence interval [CI] = 495–688 N), loaded single-leg RDL (95% CI = 500–655 N), and loaded single-leg hip thrust (95% CI = 505–640 N). The tier 1 exercises for gluteus medius were body weight side plank (95% CI = 338–483 N), loaded single-leg squat (95% CI = 278–422 N), and loaded single-leg RDL (95% CI = 283–405 N). The tier 1 exercises for gluteus minimus were loaded single-leg RDL (95% CI = 267–389 N) and body weight side plank (95% CI = 272–382 N). Peak gluteal muscle forces increased by 28–150 N when exercises were performed with 12RM external resistance compared with body weight only. Peak muscle force coincided with maximum fiber length for most exercises. Conclusions: Gluteal muscle forces were exercise specific, and peak muscle forces increased by varying amounts when adding a 12RM external resistance. These findings may inform exercise selection by facilitating the targeting of individual gluteal muscles and optimization of mechanical loads to match performance, injury prevention, or rehabilitation training goals. [ABSTRACT FROM AUTHOR]

Purpose: Sprinters exhibit inhomogeneous muscularity corresponding to musculoskeletal demand for sprinting execution. An inhomogeneous morphology would affect the mass distribution, which in turn may affect the mechanical difficulty in moving from an inertia perspective; however, the morphological characteristics of sprinters from the inertia perspective have not been examined. Here we show no corresponding differences in the normalized mass and normalized moment of inertia between the sprinters and untrained nonsprinters. Methods: We analyzed fat- and water-separated magnetic resonance images from the lower limbs of 11 male sprinters (100 m best time of 10.44–10.83 s) and 12 untrained nonsprinters. We calculated the inertial properties by identifying the tissue of each voxel and combining the literature values for each tissue density. Results: The lower-limb relative mass was significantly larger in sprinters (18.7% ± 0.7% body mass) than in nonsprinters (17.6% ± 0.6% body mass), whereas the normalized moment of inertia of the lower limb around the hip in the anatomical position was not significantly different (0.044 ± 0.002 vs 0.042 ± 0.002 [a. u.]). The thigh relative mass in sprinters (12.9% ± 0.4% body mass) was significantly larger than that in nonsprinters (11.9% ± 0.4% body mass), whereas the shank and foot relative masses were not significantly different. Conclusions: We revealed that the mechanical difficulty in swinging the lower limb is not relatively larger in sprinters in terms of inertia, even though the lower-limb mass is larger, reflecting their muscularity. We provide practical implications that sprinters can train without paying close attention to the increase in lower-limb mass and moment of inertia. [ABSTRACT FROM AUTHOR]

Purpose: Resistance exercise training (RET) attenuates age-related muscle and strength loss ("sarcopenia"). However, compared with machine-based RET, the efficacy of cost-effective, accessible elastic band RET (EB-RET) for muscle adaptive remodeling lacks supporting mechanistic evidence. Methods: Eight young (YM; 24 ± 4 yr) and eight older (OM; 68 ± 6 yr) untrained males consumed an oral stable isotope tracer (D2O) combined with serial vastus lateralis muscle biopsies to measure integrated myofibrillar protein synthesis (iMyoPS) and regulatory signaling over ~48 h before (habitual) and after an acute bout of EB-RET (6 × 12 repetitions at ~70% of one-repetition maximum). iMyoPS was determined via gas chromatography–pyrolysis–isotope ratio mass spectroscopy and regulatory signaling expression by immunoblot. Results: Habitual iMyoPS did not differ between YM and OM (1.62% ± 0.21% vs 1.43% ± 0.47%·d−1, respectively, P = 0.128). There was a significant increase in iMyoPS after EB-RET in YM (2.23% ± 0.69%·d−1, P = 0.02), but not OM (1.75% ± 0.54%·d−1, P = 0.30). EB-RET increased the phosphorylation of key anabolic signaling proteins similarly in YM and OM at 1 h postexercise, including p-IRS-1Ser636/639, p-AktSer473, p-4EBP-1Thr37/46, p-P70S6KThr389, and p-RPS6Ser240/244, whereas p-TSC2Thr1462 and p-mTORSer2448 increased only in YM (all P < 0.05). There were no differences in the expression of amino acid transporters/sensors or proteolytic markers after EB-RET. Conclusions: iMyoPS was elevated after EB-RET in YM but not OM. However, the increase in acute anabolic signaling with EB-RET was largely similar between groups. In conclusion, the capacity for EB-RET to stimulate iMyoPS may be impaired in older age. Further work may be necessary to optimize prescriptive programming in YM and OM. [ABSTRACT FROM AUTHOR]

Skeletal muscle plays a critical role in physical function and metabolic health. Muscle is a highly adaptable tissue that responds to resistance exercise (RE; loading) by hypertrophying, or during muscle disuse, RE mitigates muscle loss. Resistance exercise training (RET)–induced skeletal muscle hypertrophy is a product of external (e.g., RE programming, diet, some supplements) and internal variables (e.g., mechanotransduction, ribosomes, gene expression, satellite cells activity). RE is undeniably the most potent nonpharmacological external variable to stimulate the activation/suppression of internal variables linked to muscular hypertrophy or countering disuse-induced muscle loss. Here, we posit that despite considerable research on the impact of external variables on RET and hypertrophy, internal variables (i.e., inherent skeletal muscle biology) are dominant in regulating the extent of hypertrophy in response to external stimuli. Thus, identifying the key internal skeletal muscle–derived variables that mediate the translation of external RE variables will be pivotal to determining the most effective strategies for skeletal muscle hypertrophy in healthy persons. Such work will aid in enhancing function in clinical populations, slowing functional decline, and promoting physical mobility. We provide up-to-date, evidence-based perspectives of the mechanisms regulating RET-induced skeletal muscle hypertrophy. [ABSTRACT FROM AUTHOR]

Purpose: Resistance training induces skeletal muscle hypertrophy via the summated effects of postexercise elevations in myofibrillar protein synthesis (MyoPS) that persist for up to 48 h, although research in females is currently lacking. MyoPS is regulated by mTOR translocation and colocalization; however, the effects of resistance training on these intracellular processes are unknown. We hypothesized that MyoPS would correlate with hypertrophy only after training in both sexes and would be associated with intracellular redistribution of mTOR. Methods: Recreationally active males and females (n = 10 each) underwent 8 wk of whole-body resistance exercise three times a week. Fasted muscle biopsies were obtained immediately before (REST) and 24 and 48 h after acute resistance exercise in the untrained (UT) and trained (T) states to determine integrated MyoPS over 48 h (D2O ingestion) and intracellular mTOR colocalization (immunofluorescence microscopy). Results: Training increased (P < 0.01) muscle strength (~20%–126%), muscle thickness (~8%–11%), and average fiber cross-sectional area (~15%–20%). MyoPS increased above REST in UT (P = 0.032) and T (P < 0.01), but to a greater extent in males (~23%; P = 0.023), and was positively (P < 0.01) associated with muscle thickness and fiber cross-sectional area at T only in both males and females. mTOR colocalization with the cell periphery increased (P < 0.01) in T, irrespective of sex or acute exercise. Training increased (P ≤ 0.043) total mTOR, LAMP2 (lysosomal marker), and their colocalization (P < 0.01), although their colocalization was greater in males at 24 and 48 h independent of training status (P < 0.01). Conclusions: MyoPS during prolonged recovery from exercise is greater in males but related to muscle hypertrophy regardless of sex only in the trained state, which may be underpinned by altered mTOR localization. [ABSTRACT FROM AUTHOR]

Introduction: Low-load resistance training with blood flow restriction (LL-BFR) has emerged as a viable alternative to conventional high-load (HL) resistance training regimens. Despite increasing evidence confirming comparable muscle adaptations between LL-BFR and HL resistance exercise, only very little is known about tendinous mechanical and morphological adaptations after LL-BFR. Therefore, the aim of the present study was to examine the effects of 14 wk of LL-BFR and HL training on patellar tendon adaptations. Methods: Twenty-nine recreationally active male participants were randomly allocated into the following two groups: LL-BFR resistance training (20%–35% one-repetition maximum (1RM)) or HL resistance training (70%–85% 1RM). Both groups trained three times per week for 14 wk. One week before and after the intervention, patellar tendon mechanical and morphological properties were assessed via ultrasound and magnetic resonance imaging. In addition, changes in muscle cross-sectional area were quantified by magnetic resonance imaging and muscle strength via dynamic 1RM measurements. Results: The findings demonstrated that both LL-BFR and HL training resulted in comparable changes in patellar tendon stiffness (LL-BFR: +25.2%, P = 0.003; HL: +22.5%, P = 0.024) without significant differences between groups. Similar increases in tendon cross-sectional area were observed in HL and LL-BFR. Muscle mass and strength also significantly increased in both groups but were not statistically different between HL (+38%) and LL-BFR (+34%), except for knee extension 1RM where higher changes were seen in LL-BFR. Conclusions: The present results support the notion that both HL and LL-BFR cause substantial changes in patellar tendon properties, and the magnitude of changes is not significantly different between conditions. Further studies that examine the physiological mechanisms underlying the altered tendon properties after LL-BFR training are needed. [ABSTRACT FROM AUTHOR]

Introduction: Exercise-induced microRNA (miRNA) expression has been implicated in the regulation of skeletal muscle plasticity. However, the specificity and acute time course in miRNA expression after divergent exercisemodes are unknown. In a randomized crossover design, we compared the acute expression profile of eight skeletalmusclemiRNAs previously reported to be involved in skeletalmuscle development, growth, andmaintenance after a bout of either resistance exercise (RE), high-intensity interval exercise (HIIE), and concurrent resistance and high-intensity interval exercises (CE). Methods: Nine untrained youngmen (23.9 ± 2.8 yr, 70.1 ± 14.9 kg, 177.2 ± 3.0 cm, 41.4 ± 5.2mL·kg-1·min-1) underwent a counterbalanced crossover design in which they performed bouts of RE (2 x 10 repetitions maximum 45° leg press and leg extension exercises), HIEE (12 x 1-min sprints at VO2peak with 1-min rest intervals between sprints), and CE (RE followed by HIIE), separated by 1 wk. Vastus lateralis biopsies were harvested immediately before (Pre) and immediately (0 h), 4 h, and 8 h after each exercise bout. Results: There were similar increases (main effect of time; P < 0.05) in miR-1-3p, miR-133a-3p, miR-133b, miR-181a-3p, and miR-486 expression at 8 h from Pre with all exercise modes. Besides a main effect of time, miR-23a-3p and miR-206 presented a main effect of condition with lower expression after HIIE compared with RE and CE. Conclusions: Select miRNAs (miR-1-3p, miR-133a-3p, miR-133b, miR-23a-3p, miR-181a-3p, miR-206, miR-486) do not exhibit an expression specificity in the acute recovery period after a single bout of RE, HIIE, or CE in skeletal muscle. Our data also indicate that RE has a higher effect on the expression of miR-23a-3p and miR-206 than HIIE. As upregulation of these miRNAs seems to be confined to the 8-h period after exercise, this may subsequently affect the expression patterns of target mRNAs forming the basis of exercise-induced adaptive responses. [ABSTRACT FROM AUTHOR]

Introduction: Resistance exercise training (RET) induces muscle hypertrophy that, when combined with co-temporal protein ingestion, is enhanced. However, fewer studies have been conducted when RET is combined with multi-ingredient supplements. Purpose: We aimed to determine the effect of a high-quality multi-ingredient nutritional supplement (SUPP) versus an isonitrogenous (lower protein quality), isoenergetic placebo (PL) on RET-induced gains in lean body mass (LBM), muscle thickness, and muscle cross-sectional area (CSA). We hypothesized that RET-induced gains in LBM and muscle CSA would be greater in SUPP versus PL. Methods: In a double-blind randomized controlled trial, 26 (13 male, 13 female) healthy young adults (mean ± SD, 22 ± 2 yr) were randomized to either the SUPP group (n = 13; 20 g whey protein, 2 g leucine, 2.5 g creatine monohydrate, 300 mg calcium citrate, 1000 IU vitamin D) or the PL group (n = 13; 20 g collagen peptides, 1.4 g alanine, 0.6 g glycine) groups, ingesting their respective supplements twice daily. Measurements were obtained before and after a 10-wk linear progressive RET program. Results: Greater increases in LBM were observed for SUPP versus PL (SUPP: +4.1 ± 1.3 kg, PL: +2.8 ± 1.7 kg, P < 0.05). No additive effect of the supplement could be detected on vastus lateralis muscle CSA, but SUPP did result in increased biceps brachii muscle CSA and thickness (P < 0.05). Conclusions: We conclude that when combined with RET, the consumption of SUPP increased LBM and upper-body CSA and thickness to a greater extent than to that observed in the PL group of healthy young adults. [ABSTRACT FROM AUTHOR]

This consensus statement is an update of the 1987American College of SportsMedicine (ACSM) position stand on the use of anabolic-androgenic steroids (AAS). Substantial data have been collected since the previous position stand, and AAS use patterns have changed significantly. The ACSMacknowledges that lawful and ethical therapeutic use of AAS is now an accepted mainstream treatment for several clinical disorders; however, there is increased recognition that AAS are commonly used illicitly to enhance performance and appearance in several segments of the population, including competitive athletes. The illicit use of AAS by competitive athletes is contrary to the rules and ethics of many sport governing bodies. Thus, the ACSMdeplores the illicit use of AAS for athletic and recreational purposes. This consensus statement provides a brief history of AAS use, an update on the science of how we now understand AAS to be working metabolically/biochemically, potential side effects, the prevalence of use among athletes, and the use of AAS in clinical scenarios. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. 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. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. The biarticular hamstrings are lengthened more in a seated (hip-flexed) than prone (hip-extended) position. Purpose: We investigated the effects of seated versus prone leg curl training on hamstrings muscle hypertrophy and susceptibility to eccentric exercise-induced muscle damage. Methods: Part 1: Twenty healthy adults conducted seated leg curl training with one leg (Seated-Leg) and prone with the other (Prone-Leg), at 70% one-repetition maximum (1RM), 10 repetitions per set, 5 sets per session, 2 sessions per week for 12 wk. Magnetic resonance imaging (MRI)–measured muscle volume of the individual and whole hamstrings was assessed pre- and posttraining. Part 2: Nineteen participants from part 1 and another 12 untrained controls (Control-Leg) performed eccentric phase-only leg curl exercise at 90% 1RM, 10 repetitions per set, 3 sets for each of the seated/prone conditions with each leg. MRI-measured transverse relaxation time (T2) and 1RM of seated/prone leg curl were assessed before, 24, 48, and 72 h after exercise. Results: Part 1: Training-induced increases in muscle volume were greater in Seated-Leg versus Prone-Leg for the whole hamstrings (+14% vs +9%) and each biarticular (+8%–24% vs +4%–19%), but not monoarticular (+10% vs +9%), hamstring muscle. Part 2: After eccentric exercise, Control-Leg had greater increases in T2 in each hamstring muscle (e.g., semitendinosus at 72 h: +52%) than Seated-Leg (+4%) and Prone-Leg (+6%). Decreases in 1RM were also greater in Control-Leg (e.g., seated/prone 1RM at 24 h: −12%/−24%) than Seated-Leg (0%/−3%) and Prone-Leg (+2%/−5%). None of the changes significantly differed between Seated-Leg and Prone-Leg at any time points. Conclusion: Hamstrings muscle size can be more effectively increased by seated than prone leg curl training, suggesting that training at long muscle lengths promotes muscle hypertrophy, but both are similarly effective in reducing susceptibility to muscle damage. [ABSTRACT FROM AUTHOR]

Introduction: Several acute studies have suggested that leucine is a key amino acid to drive muscle protein synthesis. However, there are very few studies on the long-term effects of leucine supplementation on resistance training (RT)–induced gains in muscle mass and strength. We sought to determine the impact of 10 g of leucine on muscle mass and strength in response to RT in healthy young men. Methods: Twenty-five, resistance-trained men (27 ± 5 yr; 78.4 ± 11.6 kg; 24.8 ± 3.0 kg·m−2) consuming 1.8 ± 0.4 g protein·kg−1·d−1, were randomly assigned to receive 2 × 5 g·d−1 supplementation of either free leucine (LEU n = 12) or alanine (PLA n = 13) while undergoing a supervised 12-wk, twice-weekly lower-limb RT program. One-repetition maximum (leg-press 1RM) and muscle cross-sectional area (mCSA) of the vastus lateralis were determined before (PRE) and after (POST) the intervention. Additionally, three 24-h dietary recalls were also performed at PRE and POST. Results: Protein intake was roughly double that of the RDA in both groups and remained unchanged across time with no differences detected between groups. Similar increases were observed between groups in leg-press 1RM (LEU, 19.0% ± 9.4% and PLA, 21.0% ± 10.4%, P = 0.31) and mCSA (LEU, 8.0% ± 5.6% and PLA, 8.4% ± 5.1%, P = 0.77). Conclusions: High-dose leucine supplementation did not enhance gains in muscle strength and mass after a 12-wk RT program in young resistance-trained males consuming adequate amounts of dietary protein. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to compare the effects of four resistance training (RT) programs with different velocity loss (VL) thresholds: 0% (VL0), 10% (VL10), 20% (VL20), and 40% (VL40) on sprint and jump performance, muscle strength, neuromuscular, muscle hypertrophy, and architectural adaptations. Methods: Sixty-four young resistance-trained men were randomly assigned into four groups (VL0, VL10, VL20, and VL40) that differed in the VL allowed in each set. Subjects followed an RT program for 8 wk (two sessions per week) using the full-squat (SQ) exercise, with similar relative intensity (70%–85% 1-repetition maximum), number of sets (3), and interset recovery period (4 min). Before and after the RT program, the following tests were performed: 1) muscle hypertrophy and architecture of the vastus lateralis (VLA), 2) tensiomyography, 3) 20-m running sprint, 4) vertical jump, 5) maximal voluntary isometric contraction in SQ, 6) progressive loading test in SQ, and 7) fatigue test. Results: No between-group differences existed for RT-induced gains in sprint, jump, and strength performance despite the differences in the total volume performed by each group. VL20 and VL40 showed significant increases (P < 0.001) in muscle hypertrophy (group–time interaction, P = 0.06). However, only VL40 exhibited a significant slowing (P < 0.001) of the delay time in the VLA muscle (group–time interaction, P = 0.05). Moreover, VL40 showed a significant decrease in the early rate of force development (P = 0.04). Conclusions: Higher VL thresholds (i.e., VL20 and VL40) maximized hypertrophic adaptations, although an excessive VL during the set (i.e., VL40) may also induce negative neuromuscular adaptations. Therefore, moderate VL thresholds should be chosen to maximize strength adaptations and to prevent negative neuromuscular adaptations. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. Purpose: Hypertrophic cardiomyopathy (HCM) is characterized by inappropriate left ventricular (LV) wall thickness. Adaptations to exercise can occasionally mimic certain HCM characteristics. However, it is unclear whether physical activity affects HCM genotype expression and disease characteristics. Consequently, we compared lifelong physical activity volumes between HCM gene carriers with and without HCM phenotype, and compared disease characteristics among tertiles of physical activity in phenotypic HCM patients. Methods: We enrolled n = 22 genotype positive/phenotype negative (G+/P−) HCM gene carriers, n = 44 genotype positive/phenotype positive (G+/P+) HCM patients, and n = 36 genotype negative/phenotype positive (G−/P+) HCM patients. Lifelong physical activity was recorded using a questionnaire and quantified as metabolic equivalent of task hours per week. Results: We included 102 participants (51 ± 16 yr, 49% male). Lifelong physical activity volumes were not different between G+/P+ and G+/P− subjects (16 [10–29] vs 14 [6–26] metabolic equivalent of task‐hours per week, P = 0.33). Among phenotypic HCM patients, there was no difference in LV wall thickness, mass, and late gadolinium enhancement across physical activity tertiles. Patients with the highest reported physical activity volumes were younger at the time of diagnosis (tertile 1: 52 ± 14 yr, tertile 2: 49 ± 15 yr, tertile 3: 41 ± 18 yr; P = 0.03), and more often had a history of nonsustained ventricular tachycardia (4% vs 30% vs 30%, P = 0.03). Conclusions: Lifelong physical activity volumes are not associated with genotype-to-phenotype transition in HCM gene carriers. We also found no difference in LV wall thickness across physical activity tertiles. However, the most active HCM patients were younger at the time of diagnosis and had a higher arrhythmic burden. These observations warrant further exploration of the role of exercise in HCM disease development. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. Introduction: Improved myocardial contractility is a critical circulatory adaptation to exercise training. However, the types of exercise that enhance left ventricular (LV) contractile and diastolic functions have not yet been established. This study investigated how high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) influence LV mechanics during exercise. Methods: Fifty-four healthy sedentary men were randomized to engage in either HIIT (3-min intervals at 40% and 80% of V˙O2max, n = 18) or MICT (sustained 60% of V˙O2max, n = 18) for 30 min·d−1, 5 d·wk−1 for 6 wk or to a control group (n = 18) that did not engage in exercise intervention. LV mechanics during semiupright bicycle exercise tests were measured by two-dimensional speckle-tracking echocardiography. Results: Before the interventions, acute bicycle exercise increased (i) peak basal/apical radial and circumferential and peak longitudinal strains and strain rates, (ii) peak basal/apical rotations and torsion, and (iii) peak systolic twisting and early diastolic untwisting velocities in the LV. After the interventions, the HIIT group exhibited greater LV mass and diastolic internal diameter as well as higher ratio of E wave to A wave and early diastolic propagation velocity than did the MICT group. Despite decreased peak apical rotation and torsion, HIIT enhanced peak apical radial strain and strain rate as well as shortened the time to reach peak untwisting velocity in the LV during exercise. However, the LV mechanics during exercise were unchanged in the control group. Conclusion: HIIT but not MICT induces eccentric myocardial hypertrophy. Moreover, HIIT effectively improves the LV mechanics during exercise by increasing contractile and diastolic functions. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. Purpose: Combining blood flow restriction (BFR) with exercise can stimulate skeletal muscle hypertrophy. Recent observations in an animal model suggest that BFR performed without exercise can also induce anabolic effects. We assessed the effect of BFR performed both with and without low-load resistance-type exercise (LLRE) on in vivo myofibrillar protein synthesis rates in young men. Methods: Twenty healthy young men (age = 24 ± 1 yr, body mass index = 22.9 ± 0.6 kg·m−2) were randomly assigned to remain in resting condition (REST ± BFR; n = 10) or to perform LLRE (LLRE ± BFR at 20% one-repetition maximum; n = 10), combined with two 5-min cycles of single leg BFR. Myofibrillar protein synthesis rates were assessed during a 5-h post-BFR period by combining a primed continuous L-[ring-13C6]phenylalanine infusion with the collection of blood samples, and muscle biopsies from the BFR leg and the contralateral control leg. The phosphorylation status of anabolic signaling (mammalian target of rapamycin pathway) and metabolic stress (acetyl-CoA carboxylase)–related proteins, as well as the mRNA expression of genes associated with skeletal muscle mass regulation, was assessed in the collected muscle samples. Results: Under resting conditions, no differences in anabolic signaling or myofibrillar protein synthesis rates were observed between REST + BFR and REST (0.044% ± 0.004% vs 0.043% ± 0.004% per hour, respectively; P = 0.683). By contrast, LLRE + BFR increased myofibrillar protein synthesis rates by 10% ± 5% compared with LLRE (0.048% ± 0.005% vs 0.043% ± 0.004% per hour, respectively; P = 0.042). Furthermore, compared with LLRE, LLRE + BFR showed higher phosphorylation status of acetyl-CoA carboxylase and 4E-BP1 as well as the elevated mRNA expression of MuRF1 (all P < 0.05). Conclusion: BFR does not increase myofibrillar protein synthesis rates in healthy young men under resting conditions. When combined with LLRE, BFR increases postexercise myofibrillar protein synthesis rates in vivo in humans. [ABSTRACT FROM AUTHOR]

Introduction: Current athlete-specific protein recommendations are based almost exclusively on research in males. Purpose: Using the minimally invasive indicator amino acid oxidation technique, we determined the daily protein intake that maximizes whole-body protein synthesis (PS) and net protein balance (NB) after exercise in strength-trained females. Methods: Eight resistance-trained females (23 ± 3.5 yr, 67.0 ± 7.7 kg, 163.3 ± 3.7 cm, 24.4% ± 6.9% body fat; mean ± SD) completed a 2-d controlled diet during the luteal phase before performing an acute bout of whole-body resistance exercise. During recovery, participants consumed eight hourly meals providing a randomized test protein intake (0.2–2.9 g·kg−1·d−1) as crystalline amino acids modeled after egg protein, with constant phenylalanine (30.5 mg·kg−1·d−1) and excess tyrosine (40.0 mg·kg−1·d−1) intakes. Steady-state whole-body phenylalanine rate of appearance (Ra), oxidation (Ox; the reciprocal of PS), and NB (PS − Ra) were determined from oral [13C] phenylalanine ingestion. Total protein oxidation was estimated from the urinary urea–creatinine ratio (U/Cr). Results: A mixed model biphase linear regression revealed a break point (i.e., estimated average requirement) of 1.49 ± 0.44 g·kg−1·d−1 (mean ± 95% confidence interval) in Ox (r2 = 0.64) and 1.53 ± 0.32 g·kg−1·d−1 in NB (r2 = 0.65), indicating a saturation in whole-body anabolism. U/Cr increased linearly with protein intake (r2 = 0.56, P < 0.01). Conclusions: Findings from this investigation indicate that the safe protein intake (upper 95% confidence interval) to maximize anabolism and minimize protein oxidation for strength-trained females during the early ~8-h postexercise recovery period is at the upper end of the recommendations of the American College of Sports Medicine for athletes (i.e., 1.2–2.0 g·kg−1·d−1). [ABSTRACT FROM AUTHOR]

Introduction: The purpose of the present study was to compare the effects of different volumes of resistance training (RT) on muscle performance and hypertrophy in trained women. Methods: The study included 40 volunteers that performed RT for 24 wk divided into groups that performed 5 (G5), 10 (G10), 15 (G15), and 20 (G20) sets per muscle group per session. Ten-repetition maximum (10RM) tests were performed for the bench press, lat pulldown, 45° leg press, and stiff-legged deadlift. Muscle thickness (MT) was measured using ultrasound at biceps brachii, triceps brachii, pectoralis major, quadriceps femoris, and gluteus maximus. Results: All groups significantly increased all MT measures and 10RM tests after 24 wk of RT (P < 0.05). Between-group comparisons revealed no differences in any 10RM test between G5 and G10 (P > 0.05). G5 and G10 showed significantly greater 10RM increases than G15 for lat pulldown, leg press, and stiff-legged deadlift. 10RM changes for G20 were lower than all other groups for all exercises (P < 0.05). G5 and G10 showed significantly greater MT increases than G15 and G20 in all sites (P < 0.05). MT increased more in G15 than G20 in all sites (P < 0.05). G5 increases were higher than G10 for pectoralis major MT, whereas G10 showed higher increases in quadriceps MT than G5 (P < 0.05). Conclusions: Five to 10 sets per week might be sufficient for attaining gains in muscle size and strength in trained women during a 24-wk RT program. There appears no further benefit by performing higher exercise volumes. Because lack of time is a commonly cited barrier to exercise adoption, our data support RT programs that are less time consuming, which might increase participation and adherence. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. Purpose: To investigate the effects of blood flow–restricted resistance exercise (BFRRE) on myofiber areas (MFA), number of myonuclei and satellite cells (SC), muscle size and strength in powerlifters. Methods: Seventeen national level powerlifters (25 ± 6 yr [mean ± SD], 15 men) were randomly assigned to either a BFRRE group (n = 9) performing two blocks (weeks 1 and 3) of five BFRRE front squat sessions within a 6.5-wk training period, or a conventional training group (Con; n = 8) performing front squats at 60%–85% of one-repetition maximum (1RM). The BFRRE consisted of four sets (first and last set to voluntary failure) at ~30% of 1RM. Muscle biopsies were obtained from m. vastus lateralis (VL) and analyzed for MFA, myonuclei, SC and capillaries. Cross-sectional areas (CSA) of VL and m. rectus femoris were measured by ultrasonography. Strength was evaluated by maximal voluntary isokinetic torque (MVIT) in knee extension and 1RM in front squat. Results: BFRRE induced selective increases in type I MFA (BFRRE: 12% vs Con: 0%, P < 0.01) and myonuclear number (BFRRE: 18% vs Con: 0%, P = 0.02). Type II MFA was unaltered in both groups. BFRRE induced greater changes in VL CSA (7.7% vs 0.5%, P = 0.04), which correlated with the increases in MFA of type I fibers (r = 0.81, P = 0.02). No group differences were observed in SC and strength changes, although MVIT increased with BFRRE (P = 0.04), whereas 1RM increased in Con (P = 0.02). Conclusions: Two blocks of low-load BFRRE in the front squat exercise resulted in increased quadriceps CSA associated with preferential hypertrophy and myonuclear addition in type 1 fibers of national level powerlifters. [ABSTRACT FROM AUTHOR]

Leucine metabolites, α-hydroxyisocaproic acid (α-HICA) and β-hydroxy-β-methylbutyrate (calcium, HMB-Ca and free acid, HMB-FA), have been proposed to augment resistance training-induced changes in body composition and performance. Purpose: We aimed to conduct a double-blind randomized controlled pragmatic trial to evaluate the effects of off-the-shelf leucine metabolite supplements of α-HICA, HMB-FA, and HMB-Ca on resistance training-induced changes in muscle thickness and performance. Methods: Forty men were randomly assigned to receive α-HICA (n = 10, fat-free mass [FFM] = 62.0 ± 7.1 kg), HMB-FA (n = 11, FFM = 62.7 ± 10.5 kg), HMB-Ca (n = 9, FFM = 65.6 ± 10.1 kg), or placebo (PLA; n = 10, FFM = 64.2 ± 5.7 kg). The training program consisted of whole body thrice weekly resistance training for 8 wk (seven exercises per session, three to four sets per session, at 70%–80% one repetition maximum). Skeletal muscle thickness by ultrasound, performance measures, and blood measures (creatine kinase, insulin-like growth factor 1, growth hormone, cortisol, and total testosterone) were evaluated at baseline and at the end of weeks 4 and 8. Results: Time-dependent changes were observed for muscle thickness (P < 0.001), one repetition maximum bench press and squat (P < 0.001), Wingate peak power (P = 0.02), countermovement jump height (P = 0.03), power (P = 0.006), creatine kinase, insulin-like growth factor-1, growth hormone, and cortisol (all P < 0.001). No significant between-group or time–group interactions were observed. Conclusions: No leucine metabolite resulted in any ergogenic effects on any outcome variable. Supplementation with leucine metabolites—α-HICA, HMB-FA, or HMB-Ca—is not a supplementation strategy that improves muscle growth and strength development in young adult men. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. Introduction: Low-intensity endurance training (ET) performed with blood flow restriction (BFR) can improve muscle strength, cross-sectional area (CSA) and cardiorespiratory capacity. Whether muscle strength and CSA as well as cardiorespiratory capacity (i.e., V˙O2max) and underlying molecular processes regulating such respective muscle adaptations are comparable to resistance and ET is unknown. Purpose: To determine the respective chronic (i.e., 8 wk) functional, morphological, and molecular responses of ET-BFR training compared with conventional, unrestricted resistance training (RT) and ET. Methods: Thirty healthy young men were randomly assigned to one of three experimental groups: ET-BFR (n = 10, 4 d·wk−1, 30-min cycling at 40% of V˙O2max), RT (n = 10, 4 d·wk−1, 4 sets of 10 repetitions leg press at 70% of one repetition maximum with 60 s rest) or ET (n = 10, 4 d·wk−1, 30-min cycling at 70% of V˙O2max) for 8 wk. Measures of quadriceps CSA, leg press one repetition maximum, and V˙O2max as well as muscle biopsies were obtained before and after intervention. Results: Both RT and ET-BFR increased muscle strength and hypertrophy responses. ET-BFR also increased V˙O2max, total cytochrome c oxidase subunit 4 isoform 1 abundance and vascular endothelial growth factor mRNA abundance despite the lower work load compared to ET. Conclusions: Eight weeks of ET-BFR can increase muscle strength and induce similar muscle hypertrophy responses to RT while V˙O2max responses also increased postintervention even with a significantly lower work load compared with ET. Our findings provide new insight to some of the molecular mechanisms mediating adaptation responses with ET-BFR and the potential for this training protocol to improve muscle and cardiorespiratory capacity. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to evaluate muscular adaptations between low-, moderate-, and high-volume resistance training protocols in resistance-trained men. Methods: Thirty-four healthy resistance-trained men were randomly assigned to one of three experimental groups: a low-volume group performing one set per exercise per training session (n = 11), a moderate-volume group performing three sets per exercise per training session (n = 12), or a high-volume group performing five sets per exercise per training session (n = 11). Training for all routines consisted of three weekly sessions performed on nonconsecutive days for 8 wk. Muscular strength was evaluated with one repetition maximum (RM) testing for the squat and bench press. Upper-body muscle endurance was evaluated using 50% of subjects bench press 1RM performed to momentary failure. Muscle hypertrophy was evaluated using B-mode ultrasonography for the elbow flexors, elbow extensors, mid-thigh, and lateral thigh. Results: Results showed significant preintervention to postintervention increases in strength and endurance in all groups, with no significant between-group differences. Alternatively, while all groups increased muscle size in most of the measured sites from preintervention to postintervention, significant increases favoring the higher-volume conditions were seen for the elbow flexors, mid-thigh, and lateral thigh. Conclusions: Marked increases in strength and endurance can be attained by resistance-trained individuals with just three 13-min weekly sessions over an 8-wk period, and these gains are similar to that achieved with a substantially greater time commitment. Alternatively, muscle hypertrophy follows a dose–response relationship, with increasingly greater gains achieved with higher training volumes. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. Ingestion of proteins with high leucine content during resistance training (RT) can augment hypertrophy. Some data suggest that a leucine metabolite, β-hydroxy, β-methylbutyrate (HMB), is substantially more anabolically efficacious than leucine. Purpose: We aimed to test whether supplementation with HMB versus leucine, added to whey protein, would result in differential muscle hypertrophy and strength gains in young men performing RT. Methods: Twenty-six resistance-trained men (23 ± 2 yr) performed 12 wk of RT with three phases. Phase 1: 8 wk of periodized RT (three training sessions per week). Phase 2: 2 wk overreaching period (five sessions per week). Phase 3: 2 wk taper (three sessions per week). Participants were randomly assigned to twice daily ingestion of: whey protein (25 g) plus HMB (1.5 g) (whey+HMB; n = 13) or whey protein (25 g) plus leucine (1.5 g) (whey+leu; n = 13). Skeletal muscle biopsies were performed before and after RT. Measures of fat- and bone-free mass, vastus lateralis (VL) muscle thickness and muscle cross-sectional area (CSA) (both by ultrasound), muscle fiber CSA, and 1-repetition maximum (1-RM) strength tests were determined. Results: We observed increases in fat- and bone-free mass, VL muscle thickness, muscle CSA and fiber type CSA and 1-RM strength with no differences between groups at any phase. We observed no differences between groups or time–group interactions in hormone concentrations at any phase of the RT program. Conclusions: β-Hydroxy-β-methylbutyrate added to whey did not result in greater increases in any measure of muscle mass, strength, or hormonal concentration compared to leucine added to whey. Our results show that HMB is no more effective in stimulating RT-induced hypertrophy and strength gains than leucine. [ABSTRACT FROM AUTHOR]

Purpose: This investigation evaluated myocellular responses to an integrated resistance and aerobic training program during 70 d of bed rest. Methods: Training was 6 d·wk−1 on a small-footprint gravity-independent flywheel resistance and aerobic device; 3 d of maximal flywheel supine quadriceps and calf exercises with continuous rowing separated by 4 to 6 h, and 3 d of interval rowing. Vastus lateralis (VL) and soleus (SOL) muscle biopsies were obtained from eight healthy males (age, 28 ± 4 yr; BMI, 25 ± 3 kg·m−2; V˙O2max, 42 ± 6 mL·kg−1·min−1) before and after 6° head-down tilt bed rest. Vastus lateralis and SOL myosin heavy chain (MHC) I and IIa single muscle fiber size and functional characteristics, as well as overall fiber type distribution, capillarization, and metabolic enzyme activities were evaluated. Results: In the VL, MHC I size and power (absolute and normalized) were preserved. The MHC IIa fibers hypertrophied (+6%, P < 0.05) without a change in absolute power, so normalized power declined (−7%, P < 0.05). In the SOL, MHC I fibers atrophied (−9%) and absolute power declined (−17%) (P < 0.05), whereas normalized power was maintained. Size, absolute power, and normalized power were protected in the less-abundant MHC IIa fibers. Reduced MHC coexpressing hybrid fibers, generally indicative of an exercise training effect, was apparent in the VL, whereas fiber type was maintained in the SOL. Capillarization and metabolic enzymes were generally preserved or increased in VL and SOL. Conclusions: The integrated resistance and aerobic training protocol on a device maintains several key myocellular characteristics during prolonged unloading, but further refinement of the exercise approach to fully protect the SOL is warranted. [ABSTRACT FROM AUTHOR]

Purpose: American-style football (ASF) participation rates in the United States are highest among high school (HS) athletes. This study sought to compare the cardiovascular response to HS versus collegiate ASF participation. Methods: The ASF participants (HS, n = 61; collegiate, n = 87) were studied at preseason and postseason time points with echocardiography and applanation tonometry. Primary outcome variables included: left ventricular (LV) mass index, LV diastolic function (early relaxation velocity [E′]), and arterial stiffness (pulse wave velocity [PWV]). Results: High school (17.1 ± 0.4 yr) and collegiate ASF participants (18 ± 0.4 yr) experienced similar LV hypertrophy (ΔLV mass HS = 10.5 ± 10 vs collegiate = 11.2 ± 13.6 g·m−2, P = 0.97). Among HS participants, increases in LV mass were associated with stable diastolic tissue velocities (ΔE′ = −0.3 ± 2.9 cm·s−1, P = 0.40) and vascular function (ΔPWV = −0.1 ± 0.6 m·s−1, P = 0.13). In contrast, collegiate participants demonstrated a higher burden of concentric LV hypertrophy (21/87, 24% vs 7/61, 11%, P = 0.026) with concomitant reductions in diastolic tissue velocities (ΔE′: −2.0 ± 2.7 cm·s−1, P < 0.001) and increased arterial stiffness (ΔPWV: Δ0.2 ± 0.6 m·s−1, P = 0.003), changes that were influenced by linemen who had the highest post-season weight (124 ± 10 kg) and systolic blood pressure ([SBP], 138.8 ± 11 mm Hg). In multivariable analyses adjusting for age and ethnicity, body mass was an independent predictor of post-season PWV (β estimate = 0.01, P = 0.04) and E′ (β estimate = −0.04, P = 0.05), whereas SBP was an independent predictor of postseason LV mass index (β estimate = 0.18, P = 0.01) and PWV (β estimate = 0.01, P = 0.007). Conclusions: The transition from HS to college represents an important physiologic temporal data point after which differential ASF cardiovascular phenotypes manifest. Future work aimed to clarify underlying mechanisms, and the long-term clinical implications of these findings is warranted. [ABSTRACT FROM AUTHOR]

It is unclear whether the superiority of eccentric over concentric training on neuromuscular improvements is due to higher torque (mechanical loading) achievable during eccentric contractions or due to resulting greater total work. Purpose: This study aimed to examine neuromuscular adaptations after maximal eccentric versus concentric training matched for total work. Methods: Twelve males conducted single-joint isokinetic (180°·s−1) maximal eccentric contractions of the knee extensors in one leg (ECC-leg) and concentric in the other (CON-leg), 6 sets per session (3–5 sets in the initial 1–3 sessions), 2 sessions per week for 10 wk. The preceding leg performed 10 repetitions per set. The following leg conducted the equivalent volume of work. In addition to peak torque during training, agonist EMG and MRI-based anatomical cross-sectional area (ACSA) and transverse relaxation time (T2) at midthigh as reflective of neural drive, hypertrophy, and edema, respectively, were assessed weekly throughout the training period and pre- and posttraining. Whole muscle volume was also measured pre- and posttraining. Results: Torque and EMG (in trained contraction conditions) significantly increased in both legs after week 1 (W1) and week 4 (W4), respectively, with a greater degree for ECC-leg (torque +76%, EMG +73%: posttraining) than CON-leg (+28%, +20%). ACSA significantly increased after W4 in ECC-leg only (+4%: posttraining), without T2 changes throughout. Muscle volume also increased in ECC-leg only (+4%). Multiple regression analysis revealed that changes (%Δ) in EMG solely explained 53%–80% and 30%–56% of the total variance in %Δtorque through training in ECC-leg and CON-leg, respectively, with small contributions (+13%–18%) of %ΔACSA for both legs. Conclusion: Eccentric training induces greater neuromuscular changes than concentric training even when matched for total work, whereas most of the strength gains during 10-wk training are attributable to the increased neural drive. [ABSTRACT FROM AUTHOR]

Purpose: Neuromuscular electrical stimulation (NMES) is commonly used in rehabilitation settings to increase muscle mass and strength. However, the effects of NMES on muscle growth are not clear and no human studies have compared anabolic signaling between low-frequency (LF) and high-frequency (HF) NMES. The purpose of this study was to determine the skeletal muscle anabolic signaling response to an acute bout of LF- and HF-NMES. Methods: Eleven young healthy volunteers (6 men, 5 women) received an acute bout of LF-NMES (20 Hz) and HF-NMES (60 Hz). Muscle biopsies were obtained from the vastus lateralis muscle before the first NMES treatment and 30 min after each NMES treatment. Phosphorylation of the following key anabolic signaling proteins was measured by Western blot, and proteins are expressed as a ratio of phosphorylated to total: mammalian target of rapamycin, p70-S6 kinase 1, and eukaryotic initiation factor 4E binding protein 1. Results: Compared with pre-NMES, phosphorylation of mammalian target of rapamycin was upregulated 40.2% for LF-NMES ( P = 0.018) and 68.4% for HF-NMES ( P < 0.0001), and HF-NMES was 29.3% greater than LF-NMES ( P = 0.026). Phosphorylation of p70-S6 kinase 1 after HF-NMES was 96.6% higher than pre-NMES ( P = 0.001) and was not different between pre-NMES and LF-NMES (although it was 50.4% higher after LF-NMES) or LF- and HF-NMES ( P > 0.05). There were no differences between treatment conditions for eukaryotic initiation factor 4E binding protein 1 phosphorylation ( P > 0.05). Conclusions: An acute bout of LF- and HF-NMES upregulated anabolic signaling with HF-NMES producing a greater anabolic response compared with LF-NMES, suggesting that HF stimulation may provide a stronger stimulus for processes that initiate muscle hypertrophy. In addition, the stimulation frequency parameter should be considered by clinicians in the design of optimal NMES treatment protocols. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to investigate the efficacy of a 12-wk combined functional anaerobic and strength training program on neuromuscular properties and functional capacity in young adults with spastic-type cerebral palsy. Methods: A total of 17 young adults (21 ± 4 yr, 9 males, Gross Motor Function Classification System I = 11 and II = 6) were randomized to 12 wk, 3 sessions per week, of high-intensity functional anaerobic and progressive resistance training of the lower limbs ( n = 8), or a waitlist control group ( n = 9). Pre- and posttraining plantarflexor and tibialis anterior muscle volumes and composition, passive and active plantarflexor muscle properties, and functional capacity outcomes were assessed. Results: The training group had higher values compared with the control group (adjusted mean difference) at 12 wk for the following: more- and less-impaired total plantarflexor and tibialis anterior muscle volumes, maximum isometric plantarflexion strength, muscle power sprint test peak power, agility shuttle time, composite functional strength score, and 6-min walk test distance. The change in total plantarflexor muscle volume was associated with the change in plantarflexor muscle strength. There were relationships between the change in plantarflexor muscle strength and the change in functional capacity outcomes (functional strength; 6-min walk test). Conclusions: Combined functional anaerobic and strength training increased muscle size, strength, and functional capacity in young adults with cerebral palsy. The addition of anaerobic training to progressive resistance training programs assists in the transfer to improved functional capacity. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. Introduction: The myonuclear domain theory postulates that myonuclei are added to muscle fibers when increases in fiber cross-sectional area (i.e., hypertrophy) are ≥26%. However, recent studies have reported increased myonuclear content with lower levels (e.g., 12%) of muscle fiber hypertrophy. Purpose: This study aimed to determine whether a muscle fiber hypertrophy “threshold” is required to drive the addition of new myonuclei to existing muscle fibers. Methods: Studies of resistance training endurance training with or without nutrient (i.e., protein) supplementation and steroid administration with measures of muscle fiber hypertrophy and myonuclei number as primary or secondary outcomes were considered. Twenty-seven studies incorporating 62 treatment groups and 903 subjects fulfilled the inclusion criteria and were included in the analyses. Results: Muscle fiber hypertrophy of ≤10% induces increases in myonuclear content, although a significantly higher number of myonuclei are observed when muscle hypertrophy is ~22%. Additional analyses showed that age, sex, and muscle fiber type do not influence muscle fiber hypertrophy or myonuclei addition. Conclusions: Although a more consistent myonuclei addition occurs when muscle fiber hypertrophy is >22%, our results challenge the concept of a muscle hypertrophy threshold as significant myonuclei addition occurs with lower muscle hypertrophy (i.e., <10%). [ABSTRACT FROM AUTHOR]

Purpose: Protracted quadriceps muscle atrophy is observed after anterior cruciate ligament reconstruction (ACL-R). The aim of this study was to assess if quadriceps strength training with eccentric overload (CON/ECC+) is more efficient to induce muscle regeneration after ACL-R than conventional concentric/eccentric (CON/ECC) strength training. Methods: Biopsies from the vastus lateralis muscle were obtained from 37 recreational athletes after 12 wk of regular rehabilitation after ACL-R and again after 12 wk with twice a week of either conventional CON/ECC (n = 16) or CON/ECC+ (n = 21) one-legged supervised leg-press training. Immunohistochemical analyses were used to determine satellite cell (SC) number (Pax7+); activated SC number (Pax7+/MyoD+); fibers expressing myosin heavy-chain (MHC) I and II, MHC neonatal, and fiber cross-sectional area. Magnetic resonance imaging was performed to measure quadriceps cross-sectional area and isokinetic testing for the measurement of quadriceps strength. Results: CON/ECC+ induced a significantly (P = 0.002) greater increase in quadriceps cross-sectional area than did CON/ECC. There also was a significant increase in the fiber cross-sectional areas of all fiber types and in quadriceps strength, but without significant difference between training groups. Only CON/ECC+ training led to a significant (P < 0.05) increase in percent type I fibers. After training, the number of MHC I+/MHCneo+ fibers was significantly (P < 0.05) greater in the CON/ECC+ than after in the CON/ECC group. The proportion of hybrid fibers tended to decrease in both groups; percent type II fibers, SC number, and activated SC number remained unchanged. Conclusions: CON/ECC+ leads to significantly greater muscle hypertrophy compared with CON/ECC, but without the hypothesized enhancing effect on SC activation. At the same time, CON/ECC+ induces a less favorable slower muscle phenotype for strong and fast movements. [ABSTRACT FROM AUTHOR]

Although endurance exercise training promotes angiogenesis and improves metabolic health, the effect of resistance training on this process is less well defined. We hypothesized that capillarization would increase proportionally, and concurrently, with muscle fiber hypertrophy in response to resistance training in young men. Methods In this double-blind, randomized control trial, 36 men (22 ± 1 yr) were randomized to placebo or protein supplementation, and participated in 12 wk of resistance training. Skeletal muscle biopsies were collected before and after 2, 4, 8, and 12 wk of training. Immunohistochemistry assessed fiber type-specific size and capillarization. Western blot and reverse transcription polymerase chain reaction assessed proteins involved in the molecular regulation of angiogenesis. Results Resistance training effectively increased Type I (15% ± 4%; P < 0.01) and Type II fiber cross-sectional area (28% ± 5%; P < 0.0001), an effect that tended to be further enhanced with protein supplementation in Type II fibers (P = 0.078). Capillary-to-fiber ratio significantly increased in Type I (P = 0.001) and II (P = 0.015) fibers after 12 wk of resistance exercise training and was evident after only 2 wk. Capillary-to-fiber perimeter exchange index increased in the Type I fibers only (P = 0.054) after 12 wk of training. Training resulted in a reduction in vascular endothelial growth factor mRNA. A (P = 0.008), while vascular endothelial growth factor receptor 2 (P = 0.016), hypoxia-inducible factor 1α (P = 0.016), and endothelial nitric oxide synthase (P = 0.01) increased in both groups. Hypoxia-inducible factor 1α protein content was higher in the protein group (main group effect, P = 0.02), and endothelial nitric oxide synthase content demonstrated a divergent relationship (time-group interaction, P = 0.049). Conclusions This study presents novel evidence that microvascular adaptations and the molecular pathways involved are elevated after 2 wk of a 12-wk resistance training program. Increases in muscle fiber cross-sectional area are effectively matched by the changes in the microvasculature, providing further support for resistance training programs to optimize metabolic health. [ABSTRACT FROM AUTHOR]

Purpose To determine if muscle growth is important for increasing muscle strength or if changes in strength can be entirely explained from practicing the strength test. Methods Thirty-eight untrained individuals performed knee extension and chest press exercise for 8 weeks. Individuals were randomly assigned to either a high-volume training group (HYPER) or a group just performing the one repetition maximum (1RM) strength test (TEST). The HYPER group performed 4 sets to volitional failure (~8-12RM) while the TEST group performed up to 5 attempts to lift as much weight as possible one time each visit. Results Data are presented as mean (90% CI). The change in muscle size was greater in the HYPER group for both the upper and lower body at most but not all sites. The change in 1RM strength for both the upper [difference of -1.1 (-4.8, 2.4) kg] and lower body [difference of 1.0 (-0.7, 2.8) kg for dominant leg] was not different between groups (similar for non-dominant). Changes in isometric and isokinetic torque were not different between groups. The HYPER group observed a greater change in muscular endurance [difference of 2 (1, 4) repetitions] only in the dominant leg. There were no differences in the change between groups in upper body endurance. There were between group differences for exercise volume [mean (95% CI)] of the dominant [difference of 11049.3 (9254.6, 12844.0) kg] leg (similar for non-dominant) and chest press with the HYPER group completing significantly more total volume [difference of 13259.9 (9632.0, 16887.8) kg]. Conclusion These findings suggests that exercise volume nor the change in muscle size from training contributed to greater strength gains compared to just practicing the test. [ABSTRACT FROM AUTHOR]

Purpose: Sporadic inclusion body myositis (sIBM), a muscular degenerative disease in the elderly, is an inflammatory myopathy characterized by muscle weakness in the wrist flexor, quadriceps, and tibialis anterior muscles. We aimed to identify the therapeutic effect of resistance exercise (RE) in improving sIBM symptoms in an sIBM animal model. Methods: Six-week-old male Wistar rats were divided into a sham group (sham, n = 12), chloroquine-control group (CQ-con, n = 12), and chloroquine-RE group (CQ-RE, n = 12). The rats were subjected to 1 wk of exercise adaptation and 8 wk of exercise (three sessions per week). Protein expression was measured by Western blotting. Rimmed vacuoles (RV) were identified by hematoxylin and eosin staining and modified Gömöri trichrome staining, and amyloid deposition was examined by Congo red staining. Results: The effects of CQ and RE differed depending on myofiber characteristics. Soleus muscles showed abnormal autophagy in response to CQ, which increased RV generation and amyloid-β accumulation, resulting in atrophy. RE generated RV and decreased amyloid deposition in soleus muscles and also improved autophagy without generating hypertrophy. This reduced the atrophy signal transduction, resulting in decreased atrophy compared with the CQ-con group. Despite no direct effect of CQ, flexor hallucis longus muscles showed loss of mass because of reduced activity or increased inflammatory response; however, RE increased the hypertrophy signal, resulting in reduced autophagy and atrophy. Conclusions: These results demonstrate that RE had a preventive effect on sIBM induced by CQ treatment in an animal model. However, because the results were from an animal experiment, a more detailed study should be conducted over a longer period, and the effectiveness of different RE programs should also be investigated. [ABSTRACT FROM AUTHOR]

It has been proposed that protein supplementation during resistance exercise training enhances muscle hypertrophy. The degree of hypertrophy during training is controlled in part through the activation of satellite cells and myonuclear accretion. Purpose: This study aimed to determine the efficacy of protein supplementation (and the type of protein) during traditional resistance training on myofiber cross-sectional area, satellite cell content, and myonuclear addition. Methods: Healthy young men participated in supervised whole-body progressive resistance training 3 d⋅wk-1 for 12 wk. Participants were randomized to one of three groups ingesting a daily 22-g macronutrient dose of soy--dairy protein blend (PB, n = 22), whey protein isolate (WP, n = 15), or an isocaloric maltodextrin placebo (MDP, n = 17). Lean mass, vastus lateralis myofiber-type--specific cross-sectional area, satellite cell content, and myonuclear addition were assessed before and after resistance training. Results: PB and the pooled protein treatments (PB + WP = PRO) exhibited a greater whole-body lean mass %change compared with MDP (P = 0.057 for PB) and (P = 0.050 for PRO), respectively. All treatments demonstrated similar leg muscle hypertrophy and vastus lateralis myofiber-type--specific cross-sectional area (P < 0.05). Increases in myosin heavy chain I and II myofiber satellite cell content and myonuclei content were also detected after exercise training (P < 0.05). Conclusion: Protein supplementation during resistance training has a modest effect on whole-body lean mass as compared with exercise training without protein supplementation, and there was no effect on any outcome between protein supplement types (blend vs whey). However, protein supplementation did not enhance resistance exercise--induced increases in myofiber hypertrophy, satellite cell content, or myonuclear addition in young healthy men. We propose that as long as protein intake is adequate during muscle overload, the adaptations in muscle growth and function will not be influenced by protein supplementation. [ABSTRACT FROM AUTHOR]

Purpose: The aim of the present study was to investigate the effect and time course of high-frequent low-load blood flow--restricted (BFR) resistance training on rapid force capacity (i.e., rate of torque development [RTD]). Materials and Methods: Ten male subjects (22.8 ± 2.3 yr) performed four sets of knee extensor exercise (20% one-repetition maximum) to concentric failure during concurrent BFR of the thigh (100 mm Hg), and eight work-matched controls (21.9 ± 3.0 yr) trained without BFR (CON). Twenty-three training sessions were performed within 19 d. Maximal slow and fast knee joint velocity muscle strength and rapid force capacity (e.g., RTD) and evoked twitch contractile parameters were assessed before (Pre) and 5 and 12 d after (Post5 and Post12) training. Muscle biopsies were obtained Pre, after 8 d (Mid8), and 3 and 10 d after (Post3 and Post10) training to examine changes in myofiber area and expression of myocellular proteins known to be modified by cellular stress (CaMKII, annexin A6, SNO-CYS). Results: RTD remained unchanged after BFR training at Post5, while increasing 15%-20% Post12 (P < 0.01). Evoked muscle twitch parameters showed a general decline Post5 (P < 0.01) while returning to baseline levels at Post12. All contractile parameters essentially remained unchanged in CON. Elevated CaMKII was observed with BFR training at Post3 (57%) and Post10 (71%) (P < 0.05), whereas SNO-CYS increased in CON at Mid8 (P < 0.05). Conclusion: This study is the first to show that low-load resistance exercise performed with BFR leads to marked increases in rapid force capacity (RTD). However, a general delayed adaptive response was observed for voluntary contractile parameters (including RTD) in parallel with a decline and subsequent recovery in evoked contractile properties, suggesting the delayed gain in rapid force capacity mainly have a peripheral origin. [ABSTRACT FROM AUTHOR]

Purpose: Aging is associated with a gradual loss of muscle mass, which some have suggested to be accelerated by short periods of muscle disuse due to medical illness. We investigated the effect of hospitalization on skeletal muscle mass in acutely ill geriatric patients with focus on the relationship between systemic inflammatory marker C-reactive protein (CRP) and changes in muscle mass, as well as the influence of resistance training upon muscle mass. Method: Unilateral leg press resistance exercise was conducted daily during the hospital period. Outcomes included changes in whole body and regional lean mass, maximal voluntary contraction of the knee extensors, leg extension power, and functional performance. Activity level was measured using ActivPAL accelerometers, and CRP levels were obtained from blood samples. Results: Sixteen subjects completed the study (eight men and eight women, age = 84.8 ± 1.9 yr, mean ± SE). Lean mass at the midthigh region of the trained leg increased by 2.4% ± 1.1% (P < 0.05) after the intervention period. There was a negative association between changes in midthigh lean mass of the trained leg and CRP (rs = -0.53, P < 0.05). Leg extension power increased significantly in both legs (P < 0.05), with no difference observed between legs. There were no changes in maximal voluntary contraction or functional performance. Conclusion: Muscle mass is not significantly lost during short-term hospitalization of relatively high functioning and active geriatric patients although our findings are potentially affected by changes in hydration status. Resistance training during hospitalization increases skeletal muscle mass, and patients with high levels of systemic inflammation demonstrate less ability to increase or preserve muscle mass in response to resistance training during illness. [ABSTRACT FROM AUTHOR]

Purpose: Long-term exercise training is associated with characteristic cardiac adaptation, termed athlete's heart. Our research group previously characterized in vivo left ventricular (LV) function of exercise-induced cardiac hypertrophy in detail in a rat model; however, the effect of detraining on LV function is still unclear. We aimed at evaluating the reversibility of functional alterations of athlete's heart after detraining. Methods: Rats (n = 16) were divided into detrained exercised (DEx) and detrained control (DCo) groups. Trained rats swam 200 min⋅d-1 for 12 wk, and control rats were taken into water for 5 min⋅d-1. After the training period, both groups remained sedentary for 8 wk. We performed echocardiography at weeks 12 and 20 to investigate the development and regression of exercise-induced structural changes. LV pressure-volume analysis was performed to calculate cardiac functional parameters. LV samples were harvested for histological examination. Results: Echocardiography showed robust LV hypertrophy after completing the training protocol (LV mass index = 2.61 ± 0.08 DEx vs 2.04 ± 0.04 g⋅kg-1 DCo, P < 0.05). This adaptation regressed after detraining (LV mass index = 2.01 ± 0.03 vs 1.97 ± 0.05 g ⋅kg-1, n.s.), which was confirmed by postmortem measured heart weight and histological morphometry. After the 8-wk-long detraining period, a regression of the previously described exercise-induced cardiac functional alterations was observed (DEx vs DCo): stroke volume (SV; 144.8 ± 9.0 vs 143.9 ± 9.6 µL, P = 0.949), active relaxation (τ =11.5 ± 0.3 vs 11.3 ± 0.4 ms, P = 0.760), contractility (preload recruitable stroke work = 69.5 ±2.7 vs 70.9 ± 2.4 mm Hg, P = 0.709), and mechanoenergetic (mechanical efficiency = 68.7 ± 1.2 vs 69.4 ± 1.8, P = 0.742) enhancement reverted completely to control values. Myocardial stiffness remained unchanged; moreover, no fibrosis was observed after the detraining period. Conclusion: Functional consequences of exercise-induced physiological LV hypertrophy completely regressed after 8 wk of deconditioning. [ABSTRACT FROM AUTHOR]

Purpose: We sought to explore the association between the spinal cord injury (SCI) level on the cardiac structure and the function observed in elite para-cyclists. Methods: Cross-sectional echocardiographic data from 44 elite SCI hand cyclists (39.8 ± 9 yr, 68% male/32% female) stratified by the level of SCI (cervical, N= 9; T1-T5, N= 10; below T5, N= 25) and 19 non-SCI blind/visually impaired (BVI) tandem cyclists (32.4 ± 7 yr, 58% male/42% female) were analyzed before the initiation of international competition. Results: Compared with non-SCI BVI cyclists, cervical SCI para-cyclists were observed with lower indexed left ventricular (LV) mass (99.6 ± 12 vs 125 ± 20 g-m, P = 0.01), posterior wall thickness (4.5 ± 0.3 vs 5.8 ± 0.7 mm⋅m-2, P < 0.001), interventricular septal wall thickness (4.8 ± 0.5 vs 5.7 ± 0.7 mm⋅m-2; P = 0.03), and left atrial volume (21 ± 3.5 vs 28 ± 7 mL⋅m-2; P = 0.02). In multivariable analyses, cervical SCI was independently associated with decreased LV wall thickness [interventricular septum (β = -0.67, P = 0.01), posterior wall (β = -0.98, P = 0.001)], decreased LV mass (β = -21, P < 0.001), and decreased left atrial volume index (β = -6.9, P = 0.001) compared with other levels of SCI and non-SCI BVI cyclists. There were no differences in ventricular function among any of the athlete groups. Conclusion: Compared with para-cyclists with lower levels of SCI, the athletes with cervical SCI demonstrate attenuated cardiac size and concentric LV hypertrophy. [ABSTRACT FROM AUTHOR]