Muscle morphological and strength adaptations to endurance vs. resistance training

Fascicle angle (FA) is suggested to increase as a result of fiber hypertrophy and furthermore to serve as the explanatory link in the discrepancy in the relative adaptations in the anatomical cross-sectional area (CSA) and fiber CSA after resistance training (RT). In contrast to RT, the effects of endurance training on FA are unclear. The purpose of this study was therefore to investigate and compare the longitudinal effects of either progressive endurance training (END, n = 7) or RT (n = 7) in young untrained men on FA, anatomical CSA, and fiber CSA. Muscle morphological measures included the assessment of vastus lateralis FA obtained by ultrasonography and anatomical CSA by magnetic resonance imaging of the thigh and fiber CSA deduced from histochemical analyses of biopsy samples from m. vastus lateralis. Functional performance measures included VO2max and maximal voluntary contraction (MVC). The RT produced increases in FA by 23 ± 8% (p < 0.01), anatomical CSA of the knee extensor muscles by 9 ± 3% (p = 0.001), and fiber CSA by 19 ± 7% (p < 0.05). RT increased knee extensor MVC by 20 ± 5% (p < 0.001). END increased VO2max by 10 ± 2% but did not evoke changes in FA, anatomical CSA, or in fiber CSA. In conclusion, the morphological changes induced by 10 weeks of RT support that FA does indeed serve as the explanatory link in the observed discrepancy between the changes in anatomical and fiber CSA. Contrarily, 10 weeks of endurance training did not induce changes in FA, but the lack of morphological changes from END indirectly support the fact that fiber hypertrophy and FA are interrelated.     

Effect of oral DHEA on serum testosterone and adaptations to resistance training in young men.

This study examined the effects of acute dehydroepiandrosterone (DHEA) ingestion on serum steroid hormones and the effect of chronic DHEA intake on the adaptations to resistance training. In 10 young men (23 +/- 4 yr old), ingestion of 50 mg of DHEA increased serum androstenedione concentrations 150% within 60 min (P < 0.05) but did not affect serum testosterone and estrogen concentrations. An additional 19 men (23 +/- 1 yr old) participated in an 8-wk whole body resistance-training program and ingested DHEA (150 mg/day, n = 9) or placebo (n = 10) during weeks 1, 2, 4, 5, 7, and 8. Serum androstenedione concentrations were significantly (P < 0.05) increased in the DHEA-treated group after 2 and 5 wk. Serum concentrations of free and total testosterone, estrone, estradiol, estriol, lipids, and liver transaminases were unaffected by supplementation and training, while strength and lean body mass increased significantly and similarly (P < 0.05) in the men treated with placebo and DHEA. These results suggest that DHEA ingestion does not enhance serum testosterone concentrations or adaptations associated with resistance training in young men.     

Similarity in adaptations to high-resistance circuit vs. traditional strength training in resistance-trained men

To compare the effects of 8 weeks of high-resistance circuit (HRC) training (3-6 sets of 6 exercises, 6 repetition maximum [RM], ～35-second interset recovery) and traditional strength (TS) training (3-6 sets of 6 exercises, 6RM, 3-minute interset recovery) on physical performance parameters and body composition, 33 healthy men were randomly assigned to HRC, TS, or a control group. Training consisted of weight lifting 3 times a week for 8 weeks. Before and after the training, 1RM strength on bench press and half squat exercises, bench press peak power output, and body composition (dual x-ray absorptiometry ) were determined. Shuttle run and 30-second Wingate tests were also completed. Upper limb (UL) and lower limb 1RM increased equally after both TS and HRC training. The UL peak power at various loads was significantly higher at posttraining for both groups (p ≤ 0.01). Shuttle-run performance was significantly better after both HRC and TS training, however peak cycling power increased only in TS training (p ≤ 0.05). Significant decreases were found in % body fat in the HRC group only; HRC and TS training both resulted in an increased lean but not bone mass. The HRC training was as effective as TS for improving weight lifting 1RM and peak power, shuttle-run performance and lean mass. Thus, HRC training promoted a similar strength-mass adaptation as traditional training while using a shorter training session duration.     

Lactate threshold and performance adaptations to 4 weeks of training in untrained swimmers: volume vs. intensity

The purpose of this study was to investigate the impact of 4 weeks of high-intensity vs. high-volume swim training on lactate threshold (LT) characteristics and performance. Thirteen untrained swimmers with a mean age of 19.0 ± 0.5 undertook an incremental swimming test before and after 4 weeks of training for the determination of LT. Performance was evaluated by a 50-m maximum freestyle test. The swimmers were assigned to 1 of each of 2 training groups. The high-intensity group (n = 6) focused on sprint training (SP) and swam a total of 1,808 ± 210 m. The high-volume group (n = 7) followed the same program as the SP group but swam an additional 1,100 m (38% more) of endurance swimming (SP + End). A training effect was evident in both groups as seen by the similar improvements in sprint performance of the 50-m maximum time (p < 0.01), peak velocity increases and the lower value of lactate at the individual LTs (p < 0.01). Lactate threshold velocity improved only in the SP + End group from 1.20 ± 0.12 m·s(-1) pretraining to 1.32 ± 0.12 m·s(-1) posttraining (p = 0.77, effect size = 1, p < 0.01), expressed by the rightward shifts of the individual lactate-velocity curves, indicating an improvement in the aerobic capacity. Peak lactate and lactate concentrations at LT did not significantly change. In conclusion, this study was able to demonstrate that 4 weeks of either high-intensity or high-volume training was able to demonstrate similar improvements in swimming performance. In the case of lack of significant changes in lactate profiling in response to high-intensity training, we could suggest a dissociation between the 2.     

Blood flow-restricted training does not improve jump performance in untrained young men

The purpose of this study was to investigate the effect of blood flow-restricted training (BFRT) on jump performance in relation to changes in muscle strength. Seventeen untrained young men were assigned into either BFRT or normal training (NORT) groups and performed low-intensity [30-40% of one-repetition maximum (1RM)] resistance exercise (horizontal squat, 3-4 sets × 15-30 repetitions) twice a week for 10 weeks. The BFRT performed the exercise with their proximal thighs compressed by air-pressure cuffs for the purpose of blood flow restriction. Squat 1RM, muscle cross-sectional area (CSA) of quadriceps femoris, and countermovement jump (CMJ) height were measured before and after the 10-wk training period. Squat 1RM increased greater in BFRT than in NORT (19.3% vs. 9.7%, P < 0.01). Although the CSA increase was independent of groups, it tended to be larger in BFRT than in NORT (8.3% vs. 2.9%, P = 0.094). On the other hand, CMJ height did not change after the training (P = 0.51). In conclusion, the present study showed that BFRT induced muscle hypertrophy and strength increase, whereas it did not increase CMJ height in previously untrained young men. It is suggested that BFRT is ineffective in improving jump performance.     

Musculoskeletal adaptations to 16 weeks of eccentric progressive resistance training in young women

We investigated the musculoskeletal adaptations and efficacy of a whole-body eccentric progressive resistance-training (PRT) protocol in young women. Subjects (n = 37; mean age, 24.3) were randomly assigned to one of 3 groups: high-intensity eccentric PRT (HRT), low-intensity eccentric PRT (LRT), or control. Subjects performed 3 sets of 6 repetitions at 125% intensity or 3 sets of 10 repetitions at 75% intensity in the HRT and LRT groups, respectively, 2 times per week for 16 weeks. Strength was determined by the concentric 1-repetition maximum (1RM) standard. Bone mass and body composition were measured by dual-energy x-ray absorptiometry (DXA). Blood and urine samples were obtained for deoxypyridinoline, osteocalcin, creatine kinase, and creatinine. Data were analyzed by repeated-measures analysis of variance with post hoc comparisons. Strength increased 20-40% in both training groups. Lean body mass increased in the LRT (0.7 +/- 0.6 kg) and HRT (0.9 +/- 0.9 kg) groups. Bone mineral content increased (0.855 +/- 0.958 g) in the LRT group only. Deoxypyridinoline decreased and osteocalcin increased in the HRT and LRT groups, respectively. These findings suggest that submaximal eccentric training is optimal for musculoskeletal adaptations and that the intensity of eccentric training influences the early patterns of bone adaptation.     

Body composition adaptations to lower-body plyometric training: a systematic review and meta-analysis

The aim of this meta-analysis was to explore the effects of plyometric jump training (PJT) on body composition parameters among males. Relevant articles were searched in the electronic databases PubMed, MEDLINE, WOS, and SCOPUS, using the key words “ballistic”, “complex”, “explosive”, “force-velocity”, “plyometric”, “stretch-shortening cycle”, “jump”, “training”, and “body composition”. We included randomized controlled trials (RCTs) that investigating the effects of PJT in healthy male’s body composition (e.g., muscle mass; body fat), irrespective of age. From database searching 21 RCTs were included (separate experimental groups = 28; pooled number of participants = 594). Compared to control, PJT produced significant increases in total leg muscle volume (small ES = 0.55, p = 0.009), thigh muscle volume (small ES = 0.38, p = 0.043), thigh girth (large ES = 1.78, p = 0.011), calf girth (large ES = 1.89, p = 0.022), and muscle pennation angle (small ES = 0.53, p = 0.040). However, we did not find significant difference between PJT and control for muscle cross-sectional area, body fat, and skinfold thickness. Heterogeneity remained low-to-moderate for most analyses, and using the Egger’s test publication bias was not found in any of the analyses (p = 0.300–0.900). No injuries were reported among the included studies. PJT seems to be an effective and safe mode of exercise for increasing leg muscle volume, thigh muscle volume, thigh and calf girth, and muscle pennation angle. Therefore, PJT may be effective to improve muscle size and architecture, with potential implications in several clinical and sport-related contexts.     

Muscle performance and enzymatic adaptations to sprint interval training

Our purpose was to examine the effects of sprintinterval training on muscle glycolytic and oxidative enzyme activityand exercise performance. Twelve healthy men (22 ± 2 yr of age)underwent intense interval training on a cycle ergometer for 7 wk.Training consisted of 30-s maximum sprint efforts (Wingate protocol)interspersed by 2-4 min of recovery, performed three times perweek. The program began with four intervals with 4 min of recovery persession in week 1 and progressed to 10 intervals with 2.5 min of recovery per session by week7. Peak power output and total work over repeated maximal 30-s efforts and maximal oxygen consumption(O_{2 max}) weremeasured before and after the training program. Needle biopsies weretaken from vastus lateralis of nine subjects before and after theprogram and assayed for the maximal activity of hexokinase, totalglycogen phosphorylase, phosphofructokinase, lactate dehydrogenase, citrate synthase, succinate dehydrogenase, malate dehydrogenase, and3-hydroxyacyl-CoA dehydrogenase. The training program resulted insignificant increases in peak power output, total work over 30 s, andO_{2 max}. Maximalenzyme activity of hexokinase, phosphofructokinase, citrate synthase,succinate dehydrogenase, and malate dehydrogenase was alsosignificantly (P < 0.05) higherafter training. It was concluded that relatively brief but intensesprint training can result in an increase in both glycolytic andoxidative enzyme activity, maximum short-term power output, andO_{2 max}.

     

Muscle morphological and biochemical adaptations to training in obese Zucker rats

The purposes of the present study were to characterize the histochemical and enzymatic profiles of various hindlimb skeletal muscles, as well as to determine maximal O2 consumption (VO2max) and respiratory exchange ratios (R) during steady-state exercise in the obese Zucker rat. The changes that occurred in these parameters in response to a 6-wk training program were then assessed. Obese rats were randomly assigned to a sedentary or training group. Lean littermates served as a second control. Training consisted of treadmill running at 18 m/min up an 8% grade, 1.5 h/day, 5 day/wk for 6 wk. During week 6, VO2max and R during a steady-state run (74% max) were determined. After 2 days of inactivity, hindlimb muscles were excised, stained for fiber type and capillaries, and assayed for hexokinase, citrate synthase, cytochrome oxidase, and beta-hydroxyacetyl-CoA dehydrogenase. The obese sedentary rats demonstrated greater oxidative enzyme activities per gram of muscle tissue than their lean littermates, greater R values during submaximal exercise of the same relative intensity, and greater absolute VO2max values. Training resulted in a 20-56% increase in oxidative enzymes, a 10% increase in VO2max, and an increase in capillary density in the soleus and plantaris. There was no alteration in R values during exercise at 74% VO2max or in fiber type composition in response to exercise training. Results suggest that the muscle of the obese Zucker rat manifests a greater oxidative capacity than the muscle of its lean littermates. The apparent inability of the obese rat to increase its use of fat during submaximal exercise of the same relative intensity in response to training remains to be elucidated.     

Ultrastructural muscle damage in young vs. older men after high-volume, heavy-resistance strength training.

This study assessed ultrastructural muscle damage in young (20-30 yr old) vs. older (65-75 yr old) men after heavy-resistance strength training (HRST). Seven young and eight older subjects completed 9 wk of unilateral leg extension HRST. Five sets of 5-20 repetitions were performed 3 days/wk with variable resistance designed to subject the muscle to near-maximal loads during every repetition. Biopsies were taken from the vastus lateralis of both legs, and muscle damage was quantified via electron microscopy. Training resulted in a 27% strength increase in both groups (P < 0.05). In biopsies before training in the trained leg and in all biopsies from untrained leg, 0-3% of muscle fibers exhibited muscle damage in both groups (P = not significant). After HRST, 7 and 6% of fibers in the trained leg exhibited damage in the young and older men, respectively (P < 0.05, no significant group differences). Myofibrillar damage was primarily focal, confined to one to two sarcomeres. Young and older men appear to exhibit similar levels of muscle damage at baseline and after chronic HRST.     

Muscle hypertrophy response to resistance training in older women.

We conducted a 12-wk resistance training program in elderly women [mean age 69 +/- 1.0 (SE) yr] to determine whether increases in muscle strength are associated with changes in cross-sectional fiber area of the vastus lateralis muscle. Twenty-seven healthy women were randomly assigned to either a control or exercise group. The program was satisfactorily completed and adequate biopsy material obtained from 6 controls and 13 exercisers. After initial testing of baseline maximal strength, exercisers began a training regimen consisting of seven exercises that stressed primary muscle groups of the lower extremities. No active intervention was prescribed for the controls. Increases in muscle strength of the exercising subjects were significant compared with baseline values (28-115%) in all muscle groups. No significant strength changes were observed in the controls. Cross-sectional area of type II muscle fibers significantly increased in the exercisers (20.1 +/- 6.8%, P = 0.02) compared with baseline. In contrast, no significant change in type II fiber area was observed in the controls. No significant changes in type I fiber area were found in either group. We conclude that a program of resistance exercise can be safely carried out by elderly women, such a program significantly increases muscle strength, and such gains are due, at least in part, to muscle hypertrophy.     

A systematic review: plyometric training programs for young children

The purpose of this systematic review was to evaluate the efficacy and safety of plyometric training for improving motor performance in young children; to determine if this type of training could be used to improve the strength, running speed, agility, and jumping ability of children with low motor competence; and to examine the extent and quality of the current research literature. Primary research articles were selected if they (a) described the outcomes of a plyometric exercise intervention; (b) included measures of strength, balance, running speed, jumping ability, or agility; (c) included prepubertal children 5-14 years of age; and (d) used a randomized control trial or quasiexperimental design. Seven articles met the inclusion criteria for the final review. The 7 studies were judged to be of low quality (values of 4-6). Plyometric training had a large effect on improving the ability to run and jump. Preliminary evidence suggests plyometric training also had a large effect on increasing kicking distance, balance, and agility. The current evidence suggests that a twice a week program for 8-10 weeks beginning at 50-60 jumps a session and increasing exercise load weekly results in the largest changes in running and jumping performance. An alternative program for children who do not have the capability or tolerance for a twice a week program would be a low-intensity program for a longer duration. The research suggests that plyometric training is safe for children when parents provide consent, children agree to participate, and safety guidelines are built into the intervention.     

Modulation of the dystrophin-associated protein complex in response to resistance training in young and older men.

The dystrophin-associated protein complex (DAPC) is a scaffold of proteins linking the intracellular cytoskeleton with the extracellular matrix that is integral to structural stability and integrity, signaling and mechanotransduction, and force transmission. We hypothesized that the expression of DAPC component proteins would be altered by resistance loading during progressive resistance training (PRT)-mediated myofiber hypertrophy, and we investigated whether aging influenced these changes. Seventeen young (27 yr) and 13 older (65 yr) men completed 16 wk of PRT with muscle biopsies at baseline (T1), 24 h after bout 1 (T2), and 24 h after the final bout at week 16 (T3). Myofiber hypertrophy in the young (type I 31%, P < 0.005; type II 40%, P < 0.001) far exceeded hypertrophy in the old (type II only, 19.5%, P < 0.05). PRT altered protein expression for caveolin-3 (decreased 24% by T3, P < 0.01), alpha(1)-syntrophin (increased 16% by T3, P < 0.05), alpha-dystrobrevin (fell 23% from T2 to T3, P < 0.01), and dystrophin [rose acutely (30% by T2, P < 0.05) and returned to baseline by T3]. The phosphorylation state of membrane neuronal nitric oxide synthase (Ser(1417)) decreased 70% (P < 0.005) by T3, particularly in the old (81%), whereas p38 MAPK phosphorylation increased twofold by T3 in the old (P < 0.01). We conclude that component proteins of the DAPC are modulated by PRT, which may serve to improve both structural and signaling functions during load-mediated myofiber hypertrophy. The blunted hypertrophic adaptation seen in old vs. young men may have resulted from overstress, as suggested by marked p38 MAPK activation in old men only.     

Hormonal responses to resistance exercise in long-term trained and untrained middle-aged men

This cross-sectional study compared hormonal responses to resistance exercise between trained and untrained men to investigate the adaptations of the endocrine system to long-term strength training in middle-aged men. Twenty-one middle-aged men were recruited for this study and matched into a strength-trained group (SG) (n = 10) and an untrained group (UG) (n = 11). In the SG, the individuals had practiced strength training for hypertrophy for at least 3 years. Upper- and lower-body muscle strength was measured with a 1 repetition maximum (1RM) test. Blood samples were collected at rest and after multiple sets of a superset strength training protocol (SSTP), with an intensity of 75% of 1RM values. With these blood samples, the levels of total testosterone (TT), free testosterone (FT), dehydroepiandrosterone (DHEA), cortisol, and sex hormone-binding globulin (SHBG) were determined. In addition, the TT-to-cortisol ratio and TT-to-SHBG ratio were calculated. There was no difference at rest between groups in hormonal values for TT, FT, DHEA, cortisol, the TT-to-SHBG ratio, and the TT-to-cortisol ratio. There were increases after SSTP in the levels of TT, FT, DHEA, and cortisol and the TT-to-SHBG ratio in the UG, but only FT increased in the SG. The SG demonstrated lower values in the TT-to-SHBG ratio after the training session. These results suggest the presence of alterations in anabolic and catabolic hormonal responses to resistance exercise in long-term trained middle-aged men, with the trained subjects demonstrating lower responsiveness in the hormone values. Long-term trained men seem to require a higher volume of training, at least similar to their daily workout, to stimulate greater hormone responses.     

Pulmonary function in young and older athletes and untrained men

This study compared the lung volumes and pulmonary functions of older endurance-trained athletes with those of healthy sedentary age-matched controls, young athletes, and young untrained men to determine whether training affects the age-associated changes in these variables. Despite large differences in maximal 02 consumption (VO2max), the older athletes and their sedentary peers had similar values for all pulmonary variables when expressed as absolute values. However, because the older athletes were shorter than the older sedentary men, their vital capacity, total lung capacity (TLC), and forced expiratory volume in 1 s were significantly larger than those of the older sedentary men when normalized for age and height; the average values for maximal voluntary ventilation and residual volume (RV) were also larger in the older athletes when normalized for age and height, but the differences were not significant. The young trained and untrained men did not differ in any of these measures. TLC was the only pulmonary variable that was the same in the young and older men; RV and the RV-to-TLC ratio were larger, whereas all other pulmonary function and volume measures were lower in the older men compared with the younger men. The older athletes were the only group whose lung volumes and pulmonary function measures were all, except for RV, substantially greater than expected based on their age and height. Thus prolonged strenuous endurance training in these older highly trained endurance athletes appears to have altered the decline in pulmonary function and volumes associated with aging.     

Large energetic adaptations of elderly muscle to resistance and endurance training.

This study determined the cellular energetic and structural adaptations of elderly muscle to exercise training. Forty male and female subjects (69.2 +/- 0.6 yr) were assigned to a control group or 6 mo of endurance (ET) or resistance training (RT). We used magnetic resonance spectroscopy and imaging to characterize energetic properties and size of the quadriceps femoris muscle. The phosphocreatine and pH changes during exercise yielded the muscle oxidative properties, glycolytic ATP synthesis, and contractile ATP demand. Muscle biopsies taken from the same site as the magnetic resonance measurements were used to determine myosin heavy chain isoforms, metabolite concentrations, and mitochondrial volume densities. The ET group showed changes in all energetic pathways: oxidative capacity (+31%), contractile ATP demand (-21%), and glycolytic ATP supply (-56%). The RT group had a large increase in oxidative capacity (57%). Only the RT group exhibited change in structural properties: a rise in mitochondrial volume density (31%) and muscle size (10%). These results demonstrate large energetic, but smaller structural, adaptations by elderly muscle with exercise training. The rise in oxidative properties with both ET and RT suggests that the aerobic pathway is particularly sensitive to exercise training in elderly muscle. Thus elderly muscle remains adaptable to chronic exercise, with large energetic changes accompanying both ET and RT.