Training-induced Muscle Hypertrophy Research Articles

Influence of intramuscular steroid receptor content and fiber capillarization on skeletal muscle hypertrophy.

Multiple intramuscular variables have been proposed to explain the high variability in resistance training induced muscle hypertrophy across humans. This study investigated if muscular androgen receptor (AR), estrogen receptor α (ERα) and β (ERβ) content and fiber capillarization are associated with fiber and whole-muscle hypertrophy after chronic resistance training. Male (n = 11) and female (n = 10) resistance training novices (22.1 ± 2.2 years) trained their knee extensors 3×/week for 10 weeks. Vastus lateralis biopsies were taken at baseline and post the training period to determine changes in fiber type specific cross-sectional area (CSA) and fiber capillarization by immunohistochemistry and, intramuscular AR, ERα and ERβ content by Western blotting. Vastus lateralis volume was quantified by MRI-based 3D segmentation. Vastus lateralis muscle volume significantly increased over the training period (+7.22%; range: -1.82 to +18.8%, p < 0.0001) but no changes occurred in all fiber (+1.64%; range: -21 to +34%, p = 0.869), type I fiber (+1.33%; range: -24 to +41%, p = 0.952) and type II fiber CSA (+2.19%; range: -23 to +29%, p = 0.838). However, wide inter-individual ranges were found. Resistance training increased the protein expression of ERα but not ERβ and AR, and the increase in ERα content was positively related to changes in fiber CSA. Only for the type II fibers, the baseline capillary-to-fiber-perimeter index was positively related to type II fiber hypertrophy but not to whole muscle responsiveness. In conclusion, an upregulation of ERα content and an adequate initial fiber capillarization may be contributing factors implicated in muscle fiber hypertrophy responsiveness after chronic resistance training.

Effect weight training on muscular hypertrophy: a systematic review

Background and Study Aim. In the context of the growing importance of strength training, the analysis of the impact of strength loads on muscle hypertrophy becomes increasingly significant. Therefore, it is critical to comprehend both the effects of strength training on stimulating muscle growth and the potential ramifications. This study aimed to systematically analyze and collate the existing scientific evidence on the effects of weight training on muscle hypertrophy. Material and Methods. The research method involved the source selection of relevant studies from various databases, with predefined inclusion criteria. A thorough literature search was conducted, followed by data extraction focusing on study design, subject population, type of weight training, duration, and outcome measures of muscle hypertrophy. Databases such as PubMed, Google Scholar and Scopus were the primary sources of literature searches. Results. The results of this systematic review indicated evidence supporting the positive effect of weight training on muscle hypertrophy in most of the studies included. However, some studies produced controversial findings or even showed no significant impact. Factors such as variations in exercise type, intensity, and frequency also influence the outcome of weight training on muscle growth. Conclusions. While weight training has the potential to stimulate muscle hypertrophy, its effects may vary based on various factors. Therefore, selecting the correct type of exercise, setting the appropriate intensity, and planning the frequency of activity is essential in achieving optimal results. This study has strong relevance in fostering effective and safe exercise programs.It can also serve as a basis for further research in exploring other factors that may influence weight training-induced muscle hypertrophy outcomes.

Effects of Acute Loading Induced Fatigability, Acute Serum Hormone Responses and Training Volume to Individual Hypertrophy and Maximal Strength during 10 Weeks of Strength Training

This study investigated whether a strength training session-induced acute fatigue is related to individuals’ strength training adaptations in maximal force and/or muscle hypertrophy, and whether acute responses in serum testosterone (T) and growth hormone (GH) concentrations during the training sessions would be associated with individual neuromuscular adaptations. 26 males completed the 10-week strength-training intervention, which included fatiguing dynamic leg press acute loading bouts (5 x 10 RM) at weeks two, four, six, and ten. Blood samples were collected before and after the loading and after 24h of recovery for serum T, GH, and cortisol (C) concentrations at weeks 2, 6, and 10. The cross-sectional area of the vastus lateralis was measured by ultrasonography. Isometric force measurements were performed before and immediately after loadings, and loading-induced acute decrease in maximal force was reported as the fatigue percentage. The subjects were split into three groups according to the degree of training-induced muscle hypertrophy after the training period. Increases in isometric force were significant for High Responders (HR, n = 10) (by 24.3 % ± 17.2, p = 0.035) and Medium Responders (MR, n = 7) (by 23.8 % ± 5.5, p = 0.002), whereas the increase of 26.2 % (±16.5) in Low Responders (LR, n = 7) was not significant. The amount of work (cm + s) increased significantly at every measurement point in all the groups. A significant correlation was observed between the fatigue percentage and relative changes in isometric force after the training period for the whole group (R = 0.475, p = 0.022) and separately only in HR (R = 0.643, p = 0.049). Only the HR group showed increased acute serum GH concentrations at every measurement point. There was also a significant acute increase in serum T for HR at weeks 6 and 10. HR showed the strongest correlation between acute loading-induced fatigue and isometric force gains. HR was also more sensitive to acute increases in serum concentrations of T and GH after the loading. Acute fatigue and serum GH concentrations may be indicators of responsiveness to muscle strength gain and, to some extent, muscle hypertrophy.

Effects of Acute Loading Induced Fatigability, Acute Serum Hormone Responses and Training Volume to Individual Hypertrophy and Maximal Strength during 10 Weeks of Strength Training.

This study investigated whether a strength training session-induced acute fatigue is related to individuals' strength training adaptations in maximal force and/or muscle hypertrophy, and whether acute responses in serum testosterone (T) and growth hormone (GH) concentrations during the training sessions would be associated with individual neuromuscular adaptations. 26 males completed the 10-week strength-training intervention, which included fatiguing dynamic leg press acute loading bouts (5 x 10 RM) at weeks two, four, six, and ten. Blood samples were collected before and after the loading and after 24h of recovery for serum T, GH, and cortisol (C) concentrations at weeks 2, 6, and 10. The cross-sectional area of the vastus lateralis was measured by ultrasonography. Isometric force measurements were performed before and immediately after loadings, and loading-induced acute decrease in maximal force was reported as the fatigue percentage. The subjects were split into three groups according to the degree of training-induced muscle hypertrophy after the training period. Increases in isometric force were significant for High Responders (HR, n = 10) (by 24.3 % ± 17.2, p = 0.035) and Medium Responders (MR, n = 7) (by 23.8 % ± 5.5, p = 0.002), whereas the increase of 26.2 % (±16.5) in Low Responders (LR, n = 7) was not significant. The amount of work (cm + s) increased significantly at every measurement point in all the groups. A significant correlation was observed between the fatigue percentage and relative changes in isometric force after the training period for the whole group (R = 0.475, p = 0.022) and separately only in HR (R = 0.643, p = 0.049). Only the HR group showed increased acute serum GH concentrations at every measurement point. There was also a significant acute increase in serum T for HR at weeks 6 and 10. HR showed the strongest correlation between acute loading-induced fatigue and isometric force gains. HR was also more sensitive to acute increases in serum concentrations of T and GH after the loading. Acute fatigue and serum GH concentrations may be indicators of responsiveness to muscle strength gain and, to some extent, muscle hypertrophy.

The Effects of Dietary Supplements, Nutraceutical Agents, and Physical Exercise on Myostatin Levels: Hope or Hype?

Myostatin, a secreted growth factor belonging to the transforming growth factor β (TGF-β) family, performs a role in hindering muscle growth by inhibiting protein kinase B (Akt) phosphorylation and the associated activation of hypertrophy pathways (e.g., IGF-1/PI3K/Akt/mTOR pathway). In addition to pharmacological agents, some supplements and nutraceutical agents have demonstrated modulatory effects on myostatin levels; however, the clinical magnitude must be appraised with skepticism before translating the mechanistic effects into muscle hypertrophy outcomes. Here, we review the effects of dietary supplements, nutraceutical agents, and physical exercise on myostatin levels, addressing the promise and pitfalls of relevant randomized clinical trials (RCTs) to draw clinical conclusions. RCTs involving both clinical and sports populations were considered, along with wasting muscle disorders (e.g., sarcopenia) and resistance training-induced muscle hypertrophy, irrespective of disease status. Animal models were considered only to expand the mechanisms of action, and observational data were consulted to elucidate potential cutoff values. Collectively, the effects of dietary supplements, nutraceutical agents, and physical exercise on myostatin mRNA expression in skeletal muscle and serum myostatin levels are not uniform, and there may be reductions, increases, or neutral effects. Large amounts of research using resistance protocols shows that supplements or functional foods do not clearly outperform placebo for modulating myostatin levels. Thus, despite some biological hope in using supplements or certain functional foods to decrease myostatin levels, caution must be exercised not to propagate the hope of the food supplement market, select health professionals, and laypeople.

Relationship between protein intake and resistance training–induced muscle hypertrophy in middle-aged women: A pilot study

ObjectiveThe aim of this study was to observe the relationship of protein intake at each meal and daily total with change in lean tissue mass with progressive resistance exercise training (RET) in healthy middle-aged women. MethodsTwenty-two healthy Japanese women were recruited from Shiga Prefecture, Japan, and a supervised whole body RET program was conducted twice a week for 16 wk. The dietary intake was assessed using 3-d dietary records. Dual-energy x-ray absorptiometry was used to measure the whole body lean soft tissue mass (WLTM). Multiple regression analysis was performed to examine the relationship between the protein intake and RET-induced changes in the WLTM after adjusting for age, sleep quality, physical activity, and energy intake. ResultsThe 16-wk RET program caused a significant gain in the WLTM (1.46 ± 0.45%, P = 0.004). Multiple regression analysis showed that the baseline protein intake at breakfast was negatively associated with the percent change in the WLTM (β = –1.598; P = 0.022). Additionally, the percent change (β = 0.624; P = 0.018) in protein intake at breakfast was positively associated with the percent change in WLTM. ConclusionIncreasing protein intake at breakfast may contribute to RET-induced muscle hypertrophy in middle-aged women, especially among those who habitually consume low-protein levels at breakfast. However, future studies with larger sample sizes are required to confirm the importance of protein intake at breakfast.

Effects of Combining a Ketogenic Diet with Resistance Training on Body Composition, Strength, and Mechanical Power in Trained Individuals: A Narrative Review.

Ketogenic diets (KD) have gained popularity in recent years among strength-trained individuals. The present review summarizes current evidence—with a particular focus on randomized controlled trials—on the effects of KD on body composition and muscle performance (strength and power output) in strength-trained individuals. Although long-term studies (>12 weeks) are lacking, growing evidence supports the effectiveness of an ad libitum and energy-balanced KD for reducing total body and fat mass, at least in the short term. However, no or negligible benefits on body composition have been observed when comparing hypocaloric KD with conventional diets resulting in the same energy deficit. Moreover, some studies suggest that KD might impair resistance training-induced muscle hypertrophy, sometimes with concomitant decrements in muscle performance, at least when expressed in absolute units and not relative to total body mass (e.g., one-repetition maximum). KD might therefore be a beneficial strategy for promoting fat loss, although it might not be a recommendable option to gain muscle mass and strength/power. More research is needed on the adoption of strategies for avoiding the potentially detrimental effect of KD on muscle mass and strength/power (e.g., increasing protein intake, reintroduction of carbohydrates before competition). In summary, evidence is as yet scarce to support a major beneficial effect of KD on body composition or performance in strength-trained individuals. Furthermore, the long-term effectiveness and safety of this type of diet remains to be determined.

Effects of long-term athletic training on muscle morphology and tendon stiffness in preadolescence: association with jump performance

PurposeEvidence on training-induced muscle hypertrophy during preadolescence is limited and inconsistent. Possible associations of muscle strength and tendon stiffness with jumping performance are also not investigated. We investigated the thickness and pennation angle of the gastrocnemius medialis muscle (GM), as indicators for potential muscle hypertrophy in preadolescent athletes. Further, we examined the association of triceps surae muscle–tendon properties with jumping performance.MethodsEleven untrained children (9 years) and 21 similar-aged artistic gymnastic athletes participated in the study. Muscle thickness and pennation angle of the GM were measured at rest and muscle strength of the plantar flexors and Achilles tendon stiffness during maximum isometric contractions. Jumping height in squat (SJ) and countermovement jumps (CMJ) was examined using a force plate. We evaluated the influence of normalised muscle strength and tendon stiffness on jumping performance with a linear regression model.ResultsMuscle thickness and pennation angle did not differ significantly between athletes and non-athletes. In athletes, muscle strength was greater by 25% and jumping heights by 36% (SJ) and 43% (CMJ), but Achilles tendon stiffness did not differ between the two groups. The significant predictor for both jump heights was tendon stiffness in athletes and normalised muscle strength for the CMJ height in non-athletes.ConclusionLong-term artistic gymnastics training during preadolescence seems to be associated with increased muscle strength and jumping performance but not with training-induced muscle hypertrophy or altered tendon stiffness in the plantar flexors. Athletes benefit more from tendon stiffness and non-athletes more from muscle strength for increased jumping performance.

Crucial role of androgen receptor in resistance and endurance trainings-induced muscle hypertrophy through IGF-1/IGF-1R- PI3K/Akt- mTOR pathway

BackgroundAndrogen receptor (AR) has been reported to play vital roles in exercise-induced increase of muscle mass in rats, but needs to be further verified and the mechanism behind remains unclear. As AR target genes, insulin growth factor-1 (IGF-1) and IGF-1 receptor (IGF-1R) promote muscle hypertrophy through activating PI3K/Akt- mammalian target of rapamycin (mTOR) pathway, a classic pathway of muscle hypertrophy. So the main purpose of this study was using AR antagonist flutamide to demonstrate AR’s effect on training-induced muscle hypertrophy and its possible mechanism: IGF-1/IGF-1R- PI3K/Akt- mTOR pathway?MethodsForty-eight Sprague Dawley male rats aged 7 weeks were randomly divided into six groups: control (C), flutamide (F), resistance training (R), resistance training plus flutamide (R + F), endurance training (E), and endurance training plus flutamide (E + F) groups. Flutamide was used to block AR in rats. Rats in R and R + F groups fulfilled 3 weeks of ladder climbing with progressively increased load, while E and E + F rats completed 3-week moderate intensity aerobic exercise on a treadmill. The relative muscle mass (muscle mass/body weight) of rats was detected. Serum levels of testosterone and IGF-1 of rats were determined by ELISA, and mRNA levels of IGF-1R and mTOR in muscles by real-time PCR. Protein levels of AR, IGF-1, IGF-1R, mTOR, PI3K, Akt, p-PI3K and p-Akt in muscles were detected by Western blot.Results(1) The training-induced rise in the relative muscle mass and the expression levels of AR were only found in the gastrocnemius of R rats and in the soleus of E rats (selective muscle hypertrophy), which were blocked by flutamide. (2) Serum testosterone in the R and E rat were increased, and flutamide exerted no effect. (3) The levels of IGF-1, IGF-1R and mTOR as well as the activities of PI3K and Akt were enhanced selectively (in the gastrocnemius of R rats and in the soleus of E rats), which were reduced by flutamide. Conclusions: AR exerted an essential role in both resistance training and endurance training-induced muscle hypertrophy, which was mediated at least partly through IGF-1/IGF-1R- PI3K/Akt- mTOR pathway.

Resistance training-induced muscle hypertrophy is mediated by TGF-β1-Smad signaling pathway in male Wistar rats.

The TGF-β1-Smad pathway is a well-known negative regulator of muscle growth; however, its potential role in resistance training-induced muscle hypertrophy is not clear. The present study proposed to determine whether and how this pathway may be involved in resistance training-induced muscle hypertrophy. Skeletal muscle samples were collected from the control, trained (RT), control + SB431542 (CITGF ), and trained + SB431542 (RTITGF ) animals following 3, 5, and 8 weeks of resistance training. Inhibition of the TGF-β1-Smad pathway by SB431542 augmented muscle satellite cells activation, upregulated Akt/mTOR/S6K1 pathway, and attenuated FOXO1 and FOXO3a expression in the CITGF group (all p < .01), thereby causing significant muscle hypertrophy in animals from the CITGF . Resistance training significantly decreased muscle TGF-β1 expression and Smad3 (P-Smad3S423/425 ) phosphorylation at COOH-terminal residues, augmented Smad2 (P-Smad2-LS245/250/255 ) and Smad3 (P-Smad3-LSer208 ) phosphorylation levels at linker sites (all p < .01), and led to a muscle hypertrophy which was unaffected by SB431542, suggesting that the TGF-β1-Smad signaling pathway is involved in resistance training-induced muscle hypertrophy. The effects of inhibiting the TGF-β1-Smad signaling pathway were not additive to the resistance training effects on FOXO1 and FOXO3a expression, muscle satellite cells activation, and the Akt/mTOR/S6K1 pathway. Resistance training effect of satellite cell differentiation was independent of the TGF-β1-Smad signaling pathway. These results suggested that the effect of the TGF-β1-Smad signaling pathway on resistance training-induced muscle hypertrophy can be attributed mainly to its diminished inhibitory effects on satellite cell activation and protein synthesis. Suppressed P-Smad3S423/425 and enhanced P-Smad2-LS245/250/255 and P-Smad3-LSer208 are the molecular mechanisms that link the TGF-β1-Smad signaling pathway to resistance training-induced muscle hypertrophy.

Influence of shortened recovery between resistance exercise sessions on muscle-hypertrophic effect in rat skeletal muscle.

Resistance exercise training induces muscle hypertrophy, and recovery between sessions is one of the major determinants of this effect. However, the effect of the recovery period between sessions on muscle hypertrophy following resistance exercise training remains unclear. To elucidate the effect of recovery period on hypertrophy, in the present study, we investigated changes in protein degradation systems and hypertrophic responses in rat skeletal muscle to resistance training with variable recovery periods. In the conventional recovery group (exercised every 72 h) and a shorter recovery group (exercised every 24 h), 18 bouts of resistance exercise consisting of 50 repetitions of a 3‐sec maximal isometric contraction caused muscle hypertrophy and slight activation of muscle protein degradation systems. By contrast, in an excessively shorter recovery group (exercised every 8 h), 18 bouts of resistance exercise did not cause hypertrophy and markedly activated protein degradation systems, accompanied by inflammatory responses. These observations indicate that excessive shortening of recovery between sessions does not cause skeletal muscle hypertrophy, likely due to the activation of proteolysis induced by inflammatory responses to resistance exercise training.

Twenty-Four Months' Resistance and Endurance Training Improves Muscle Size and Physical Functions but Not Muscle Quality in Older Adults Requiring Long-Term Care.

To assess the effects of 24 months training on muscle quality, size, strength, and gait abilities in older adults who need long-term care. Non-randomized controlled trial Setting: Kawai Rehabilitation Center and Kajinoki Medical Clinic. Ten older participants who needed long-term care (age, 76.7 ± 5.6 years) were participated as training group (Tr-group) and 10 older men and women who did not require long-term care (age, 72.9 ± 6.6 years) comprised the control group (Cont-group). Tr-group performed resistive and endurance exercises once or twice a week for 24 months. Using ultrasound images, echo intensity (EI) and muscle thickness were measured in the rectus femoris and biceps femoris as an index of muscle quality and size. Physical performance was measured before and after the training; performance parameters included knee extension peak torque, 5-m normal and maximal walk test, sit-to-stand and timed up and go test. After the training, there was no change in EI, while BF thickness was increased (pre; 1.82 ± 0.29 cm, 24 months; 2.14 ± 0.23 cm, p < 0.05) in Tr-group. Walk-related performances were improved after the training in Tr-group (i.e. 5-m walk test and timed up and go test). The percent change of knee extension peak torque explained the percent change of EI in the rectus femoris (regression coefficient = 1.24, R = 0.91, adjusted R2 = 0.82, p < 0.001). Twenty-four months' training induced muscle hypertrophy and improved physical functions. Increased muscle quality in the rectus femoris could be a key to improved knee extension peak torque, with the potential to eventually reduce the need for long-term care in older individuals.

Eccentric cycling does not improve cycling performance in amateur cyclists.

Eccentric cycling training induces muscle hypertrophy and increases joint power output in non-athletes. Moreover, eccentric cycling can be considered a movement-specific type of strength training for cyclists, but it is hitherto unknown if eccentric cycling training can improve cycling performance in trained cyclists. Twenty-three male amateur cyclists were randomized to an eccentric or a concentric cycling training group. The eccentric cycling was performed at a low cadence (~40 revolution per minute) and the intensity was controlled by perceived effort (12–17 on the Borgs scale) during 2 min intervals (repeated 5–8 times). The cadence and perceived effort of the concentric group matched those of the eccentric group. Additionally, after the eccentric or concentric cycling, both groups performed traditionally aerobic intervals with freely chosen cadence in the same session (4–5 x 4–15 min). The participants trained twice a week for 10 weeks. Maximal oxygen uptake (VO2max), maximal aerobic power output (Wmax), lactate threshold, isokinetic strength, muscle thickness, pedaling characteristics and cycling performance (6- and 30-sec sprints and a 20-min time trial test) were assessed before and after the intervention period. Inferences about the true value of the effects were evaluated using probabilistic magnitude-based inferences. Eccentric cycling induced muscle hypertrophy (2.3 ± 2.5% more than concentric) and augmented eccentric strength (8.8 ± 5.9% more than concentric), but these small magnitude effects seemed not to transfer into improvements in the physiological assessments or cycling performance. On the contrary, the eccentric training appeared to have limiting or detrimental effects on cycling performance, measured as Wmax and a 20-min time trial. In conclusion, eccentric cycling training did not improve cycling performance in amateur cyclists. Further research is required to ascertain whether the present findings reflect an actual lack of efficacy, negative effects or a delayed response to eccentric cycling training.

Oral Supplementation Using Gamma-Aminobutyric Acid and Whey Protein Improves Whole Body Fat-Free Mass in Men After Resistance Training.

BackgroundOral gamma-aminobutyric acid (GABA) supplementation increases growth hormone (GH) serum levels and protein synthesis. Therefore, post-exercise supplementation using GABA and protein may help enhance training-induced muscle hypertrophy. We evaluated whether GABA with whey protein enhanced muscular hypertrophy in men after progressive resistance training.MethodsTwenty-one healthy men (26 - 48 years) were randomized to receive whey protein (WP; 10 g) or whey protein + GABA (WP + GABA; 10 g + 100 mg) daily for 12 weeks. Both groups performed resistance training twice per week (three sets of 12 repetitions at 60% of maximal strength; leg press, leg extension, leg curl, chest press, and pull down). Body composition was assessed using dual-energy X-ray absorptiometry.ResultsIn the WP + GABA group, resting plasma GH concentrations were significantly elevated at 4 and 8 weeks, compared to baseline. However, resting plasma GH concentrations in the WP group were only significantly elevated at 8 weeks. After 12 weeks, the WP + GABA group exhibited significantly greater increase in whole body fat-free mass than the WP group.ConclusionsThe GABA and whey protein combination was more effective for increasing whole body fat-free mass; daily GABA supplementation may help enhance exercise-induced muscle hypertrophy.

Resistance Training-Induced Muscle Hypertrophy is Related to Androgen Receptor Content not Intramuscular or Systemic Hormones

Resistance Training-Induced Muscle Hypertrophy is Related to Androgen Receptor Content not Intramuscular or Systemic Hormones

Relationship between Dietary Protein or Essential Amino Acid Intake and Training-Induced Muscle Hypertrophy among Older Individuals.

Dietary protein intake is critical for maintaining an optimal muscle mass, especially among older individuals. Although protein supplementation during resistance training (RT) has been shown to further augment training-induced muscle mass in older individuals, the impact of daily variations in protein intake on training-induced muscle mass has not been explored thus far. Therefore, this study aimed to investigate the relationship between the dietary protein and amino acid intake and RT-induced muscle hypertrophy among older individuals. Ten healthy older men (n=10; mean age=69±2 y; body weight (BW)=61.5±2.2 kg; height=1.65±0.02 m) participated in progressive RT performed 3 times/wk for 12 wk. Body composition (using DXA) and nutritional assessments (using a 3-d dietary record) were performed before and after the training period. Leg lean mass (LLM) increased significantly (15.0±0.8 vs. 15.4±0.8 kg, p<0.05) after RT, with no change in dietary nutrient intake. The average dietary protein intake was 1.62±0.11 g/kg BW/d, while essential amino acids was 600±51 mg/kg BW/d. Although the correlation between the increase in LLM and dietary protein intake was not significant, a significant correlation was found between the increase in LLM and dietary essential amino acid (EAA) intake. Furthermore, there were significant correlations between the increase in LLM and protein as well as EAA (especially leucine) intake at breakfast among subjects with suboptimal protein intake (p<0.05). Our study findings indicate that dietary protein as well as EAA intake may be significant contributing factors in muscle hypertrophic response during RT among healthy older men.

Combined effects of resistance training and calorie restriction on mitochondrial fusion and fission proteins in rat skeletal muscle.

Recent studies have demonstrated that resistance exercise leads not only to muscle hypertrophy, but it also improves mitochondrial function. Because calorie restriction (CR) has been suggested as a way to induce mitochondrial biogenesis, we examined the effects of resistance training with or without CR on muscle weight and key mitochondrial parameters in rat skeletal muscle. Four weeks of resistance training (thrice/wk) resulted in increased gastrocnemius muscle weight by 14% in rats fed ad libitum (AL). The degree of muscle-weight increase via resistance training was lower in rats with CR (7.4%). CR showed no effect on phosphorylation of mammalian target of rapamycin (mTOR) signaling proteins rpS6 and ULK1. Our results revealed that CR resulted in elevated levels of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) protein, a known master regulator of mitochondrial biogenesis. Resistance training alone also resulted in increased PGC-1α levels in skeletal muscle. The magnitude of the increase in PGC-1α was similar in rats in both the CR and AL groups. Moreover, we found that resistance training with CR resulted in elevated levels of proteins involved in mitochondrial fusion (Opa1 and Mfn1), and oxidative phosphorylation, whereas there was no effect of CR on the fission-regulatory proteins Fis1 and Drp1. These results indicate that CR attenuates resistance training-induced muscle hypertrophy, and that it may enhance mitochondrial adaptations in skeletal muscle.

Resistance Training-induced Muscle Hypertrophy Is Not Determined By Repetition-load In Resistance-trained Men

We have previously shown that performing resistance exercise (RE) with high or low repetition-loads resulted in similar acute (protein turnover) and chronic (hypertrophy) adaptations. However, these studies were performed in RE-naïve trainees using unilateral leg exercises. Here we aimed to determine the effect of repetition-load on skeletal muscle hypertrophy and strength with a 12wk, whole-body RE intervention in RE-trained (RET) young men. We also evaluated the change and correlations of the post-RE rise in systemic hormone concentrations in relation to changes in skeletal muscle hypertrophy and strength. Forty-nine RET men (mean ± SEM, 23 ± 1 y, 86 ± 2 kg, 181 ± 1 cm) were randomly allocated into a high-repetition (lower load - 30-50% 1RM) group (HR: 20-25 repetitions/set, n=24) or a low-repetition (higher load - 70-90% 1RM) group (LR, 8-12 repetitions/set, n=25). Muscular strength increased for all exercises (p <0.01) and only the change in bench press was different between groups (HR; 9 ± 1, LR; 14 ±1 kg, p < 0.05). Lean body mass, type I and type II muscle fiber cross sectional area all increased following training (p < 0.01) with no significant differences between groups. There was no change in fibre type distribution pre- to post-intervention and no differences between groups. The acute post-RE rise in systemic hormones did not change as a result of training. The post-RE rise in total testosterone, insulin-like growth factor-1 and growth hormone had no correlation with any strength or hypertrophy outcome. These data show that in RET individuals repetition-load is a determinant of neither strength nor hypertrophic gains when RE is performed to volitional failure. In accordance with our previous findings we conclude that the post-RE rise in systemic hormones is not associated with or in any way predictive of changes in skeletal muscle hypertrophy or strength.

Time Course of Resistance Training–Induced Muscle Hypertrophy in the Elderly

Extended periods of resistance training (RT) induce muscle hypertrophy. Nevertheless, to date, no study has investigated the time window necessary to observe significant changes in muscle cross-sectional area (CSA) in older adults. Therefore, this study investigated the time course of muscle hypertrophy after 10 weeks (20 sessions) of RT in the elderly. Fourteen healthy older subjects were randomly allocated in either the RT (n: 6) or control group (n: 8). The RT was composed of 4 sets × 10 repetitions (70-80% 1 repetition maximum [1RM]) in a leg press machine. The time course of vastus lateralis muscle hypertrophy (CSA) was assessed on a weekly basis by mode-B ultrasonography. Leg press muscle strength was assessed by dynamic 1RM test. Our results demonstrated that the RT group increased leg press 1RM by 42% (p ≤ 0.05) after 10 weeks of training. Significant increases in vastus lateralis muscle CSA were observed only after 18 sessions of training (9 weeks; p ≤ 0.05; 7.1%). In conclusion, our training protocol promoted muscle mass accrual in older subjects, and this was only observable after 18 sessions of RT (9 weeks).

SUN-LB020: The Relationship Between Dietary Amino Acids Intake and Training-Induced Muscle Hypertrophy Among Older Individuals

SUN-LB020: The Relationship Between Dietary Amino Acids Intake and Training-Induced Muscle Hypertrophy Among Older Individuals