This study examined the force-velocity and power-velocity relationships of the quadriceps muscles of children and adults. Measurements of muscle function were collected using the Con-Trex isokinetic dynamometer. Twenty adults and twenty children performed maximal effort knee extensions at nine different velocities. The mean force-velocity curves of children and adults revealed obvious differences between the groups. The curves remained different following corrections of torque for CSA and velocity for length. ANOVA revealed significant differences in the uncorrected values of power between the two groups. When power values were corrected for lean thigh muscle volume, no significant differences were found between the groups. These findings suggest that differences in muscle strength between children and adults are a function of muscle size and imply that muscle function remains relatively unchanged from childhood to early adulthood.
Ursula Barrett and Drew Harrison
Yuya Watanabe, Michiya Tanimoto, Akane Ohgane, Kiyoshi Sanada, Motohiko Miyachi and Naokata Ishii
The authors investigated the effects of low-intensity resistance training on muscle size and strength in older men and women. Thirty-five participants (age 59–76 yr) were randomly assigned to 2 groups and performed low-intensity (50% of 1-repetition maximum) knee-extension and -flexion exercises with either slow movement and tonic force generation (LST; 3-s eccentric, 3-s concentric, and 1-s isometric actions with no rest between repetitions) or normal speed (LN; 1-s concentric and 1-s eccentric actions with 1-s rests between repetitions) twice a week for 12 wk (2-wk preparation and 10-wk intervention). The LST significantly increased thigh-muscle thickness, as well as isometric knee-extension and -flexion strength. The LN significantly improved strength, but its hypertrophic effect was limited. These results indicate that even for older individuals, the LST can be an effective method for gaining muscle mass and strength.
Wayne W. Campbell, Lyndon J.O. Joseph, Richard A. Anderson, Stephanie L. Davey, Jeremy Hinton and William J. Evans
This study assessed the effect of resistive training (RT), with or without high-dose chromium picolinate (Cr-pic) supplementation, on body composition and skeletal muscle size of older women. Seventeen sedentary women, age range 54-71 years. BMI 28.8±2.4 kg/m2. were randomly assigned (double-blind) to groups (Cr-pic. n = 9; Placebo, n = 8) that consumed either 924 μg Cr/d as Cr-pic or a low-Cr placebo (<0.2 μg Cr/d) during a 12-week RT program (2 day/ week, 3 sets · exercise−1 · d1,80% of 1 repetition maximum). Urinary chromium excretion was 60-fold higher in the Cr-pic group, compared to the Placebo group (p < .001), during the intervention. Resistive training increased maximal strength of the muscle groups trained by 8 to 34% (p < .001), and these responses were not influenced by Cr-pic supplementation. Percent body fat and fat-free mass were unchanged with RT in these weight-stable women, independent of Cr-pic supplementation. Type I and type II muscle fiber areas of the m. vastus lateralis were not changed over time and were not influenced by Cr-pic supplementation. These data demonstrate that high-dose Cr-pic supplementation did not increase maximal strength above that of resistive training alone in older women. Further, these data show that, under these experimental conditions, whole body composition and skeletal muscle size were not significantly changed due to resistive training and were not influenced by supplemental chromium picolinate.
Alon Eliakim, Mark Y. Moromisato, David Y. Moromisato and Dan M. Cooper
In this study, the hypothesis that improvements in functional and structural measures could be detected in the young, female rat with only 5 days of moderate treadmill training was tested. Eight-week-old female Sprague-Dawley rats were divided randomly into control (n = 10) and training groups (n = 11). Over the 5-day period, running duration and treadmill speed increased progressively. Maximal running time and gas exchange were measured on Day 6. In trained compared with control rats, maximal running time was 54% greater (p < .005), right hindlimb muscle was 16% heavier (p < .01), and end-exercise respiratory exchange ratio (RER) was 17% lower (p < .05). Substantial metabolic and structural adaptations occurred in young female rats after only 5 days of treadmill training. This protocol may be useful in discovering the initiating mechanisms of the training response in the young organism.
Louise E. Wood, Sharon Dixon, Chris Grant and Neil Armstrong
The aim of this study was to examine elbow flexion torque, muscle cross-sectional area (CSA), and leverage in boys and girls. Thirty-eight prepubertal children (9.6 ± 0.3 years) volunteered to participate. All performed isometric flexion actions at 10°, 50°, and 90° of elbow flexion. Magnetic resonance imaging was used to assess elbow flexor (EF) muscle CSA and brachialis moment arm lengths. No significant gender differences were observed for any of the variables studied. EF CSA was directly proportional to isometric torque at 50° and 90°. CSA explained between 47% and 57% of torque variance. Moment arm estimates explained 19% of the variance in isometric torque at 90°. These baseline data contribute to our understanding of factors influencing strength variation during childhood.
Leila Ghamkhar, Somayeh Amiri Arimi and Amir H. Kahlaee
increased JRE, smaller extensor muscles size, and reduced extensor endurance in comparison with the control group and (2) JRE, extensor muscles size, and cervical endurance are associated with the chronic nonspecific NP odds ratio. Methods Participants A total of 60 subjects aged 20–55 years volunteered to
Conall F. Murtagh, Christopher Nulty, Jos Vanrenterghem, Andrew O’Boyle, Ryland Morgans, Barry Drust and Robert M. Erskine
. Therefore, the present soccer talent selection models are limited. Subsequently, the aims of this study were to (1) investigate the differences in muscle strength, size, architecture, and activation between elite and nonelite soccer players and (2) determine the contribution of muscle size, architecture
Kevin R. Short and K. Sreekumaran Nair
Loss of muscle mass, strength, and oxidative capacity accompanies normal aging in humans. The mechanisms responsible for these changes remain to be clearly defined. Muscle protein mass and function depend on protein turnover. Synthesis rate of the major muscle contractile protein, myosin heavy chain (MHC), and transcript levels of fast MHC isoforms decrease in association with strength reductions, while mitochondrial protein synthesis rate declines in parallel with activities of mitochondrial enzymes and maximal oxidative capacity (V̇O2max). Resistance exercise training increases the synthesis rate of MHC and transcript levels of the slow MHC isoform in older humans, along with increasing muscle strength. The relationship between the synthesis of muscle proteins, and muscle size and function, with aging and exercise training are discussed in this review.
Krissy D. Weisgarber, Darren G. Candow and Emelie S. M. Vogt
To determine the effects of whey protein before and during resistance exercise (RE) on body composition and strength in young adults.
Participants were randomized to ingest whey protein (PRO; 0.3 g/kg protein; n = 9, 24.58 ± 1.8 yr, 88.3 ± 17.1 kg, 172.5 ± 8.0 cm) or placebo (PLA; 0.2 g/kg cornstarch maltodextrin + 0.1 g/kg sucrose; n = 8, 23.6 ± 4.4 yr, 82.6 ± 16.1 kg, 169.4 ± 9.2 cm) during RE (3 sets of 6–10 repetitions for 9 whole-body exercises), which was performed 4 d/wk for 8 wk. PRO and PLA were mixed with water (600 ml); 50% of the solution containing 0.15 g/kg of PRO or PLA was consumed immediately before the start of exercise, and ~1.9% of the remaining solution containing ~0.006 g/kg of PRO or PLA was consumed immediately after each training set. Before and after the study, measures were taken for leantissue mass (dual-energy X-ray absorptiometry), muscle size of the elbow and knee flexors and extensors and ankle dorsiflexors and plantar flexors (ultrasound), and muscle strength (1-repetition-maximum chest press).
There was a significant increase (p < .05) in muscle size of the knee extensors (PRO 0.6 ± 0.4 cm, PLA 0.1 ± 0.5 cm), knee flexors (PRO 0.4 ± 0.6 cm, PLA 0.5 ± 0.7 cm) and ankle plantar flexors (PRO 0.6 ± 0.7 cm, PLA 0.8 ± 1.4 cm) and chest-press strength (PRO 16.6 ± 11.1 kg, PLA 9.1 ± 14.6 kg) over time, with no differences between groups.
The ingestion of whey protein immediately before the start of exercise and again after each training set has no effect on muscle mass and strength in untrained young adults.
Thomas W. Balon, Jeffrey F. Horowitz and Karen M. Fitzsimmons
Bodybuilders have used different carbohydrate loading regimens in conjunction with resistance exercise prior to competition in the belief that this would result in increased muscle size. To investigate this possibility, muscle girth measurements were obtained from nine weight-trained males before and after a control (standard isocaloric diet) and an experimental trial (carbohydrate loading). The latter regimen consisted of 3 days of intense weight-lifting while the subjects ingested a diet of 10% carbohydrate (CHO), 57% fat (F), and 33% protein (P), followed by 3 days of light weight-lifting and a day of rest while ingesting a diet of 80% CHO, 5% F, and 15% P. The control trial consisted of an identical weight-lifting regimen while subjects ingested an isocaloric (45 kcal/kg BWIday) diet. Body weight and girths (forearm, upper arm, chest, thigh, waist, and calf) were obtained before and after each trial in a relaxed and flexed state. The results indicated that an exercise/carbohydrate loading regimen had no significant effect on muscle girth as compared to the control trial. It is concluded that CHO loading has no additional advantage to enhancing muscle girth in bodybuilders over weight-lifting alone.