Exercise-associated differences in an array of proteins involved in signal transduction and glucose transport.
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Vastus lateralis muscle biopsies were obtained from endurance-trained (running approximately 50 km/wk) and untrained (no regular physical exercise) men, and the expression of an array of insulin-signaling intermediates was determined. Expression of insulin receptor and insulin receptor substrate-1 and -2 was decreased 44% (P < 0.05), 57% (P < 0.001), and 77% (P < 0.001), respectively, in trained vs. untrained muscle. The downstream signaling target, Akt kinase, was not altered in trained subjects. Components of the mitogenic signaling cascade were also assessed. Extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase expression was 190% greater (P < 0.05), whereas p38 mitogen-activated protein kinase expression was 32% lower (P < 0.05), in trained vs. untrained muscle. GLUT-4 protein expression was twofold higher (P < 0.05), and the GLUT-4 vesicle-associated protein, the insulin-regulated aminopeptidase, was increased 4.7-fold (P < 0. 05) in trained muscle. In conclusion, the expression of proteins involved in signal transduction is altered in skeletal muscle from well-trained athletes. Downregulation of early components of the insulin-signaling cascade may occur in response to increased insulin sensitivity associated with endurance training. (+info)
Training, muscle volume, and energy expenditure in nonobese American girls.
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Little is known about the relationship among training, energy expenditure, muscle volume, and fitness in prepubertal girls. Because physical activity is high in prepubertal children, we hypothesized that there would be no effect of training. Forty pre- and early pubertal (mean age 9.1 +/- 0.1 yr) nonobese girls enrolled in a 5 day/wk summer school program for 5 wk and were randomized to control (n = 20) or training groups (n = 20; 1.5 h/day, endurance-type exercise). Total energy expenditure (TEE) was measured using doubly labeled water, thigh muscle volume using magnetic resonance imaging, and peak O(2) uptake (VO(2 peak)) using cycle ergometry. TEE was significantly greater (17%, P < 0.02) in the training girls. Training increased thigh muscle volume (+4.3 +/- 0.9%, P < 0.005) and VO(2 peak) (+9.5 +/- 6%, P < 0.05), effects surprisingly similar to those observed in adolescent girls using the same protocol (Eliakim A, Barstow TJ, Brasel JA, Ajie H, Lee W-NP, Renslo R, Berman N, and Cooper DM, J Pediatr 129: 537-543, 1996). We further compared these two sample populations: thigh muscle volume per weight was much lower in adolescent compared with prepubertal girls (17.0 +/- 0.3 vs. 27.8 +/- 0.6 ml/kg body mass; P < 0.001), and allometric analysis revealed remarkably low scaling factors relating muscle volume (0.34 +/- 0.05, P < 0.0001), TEE (0.24 +/- 0. 06, P < 0.0004), and VO(2 peak) (0.28 +/- 0.07, P < 0.0001) to body mass in all subjects. Muscle and cardiorespiratory functions were quite responsive to brief training in prepubertal girls. Moreover, a retrospective, cross-sectional analysis suggests that increases in muscle mass and VO(2 peak) may be depressed in nonobese American girls as they mature. (+info)
Physical exercise and normobaric hypoxia: independent modulators of peripheral cholecystokinin metabolism in man.
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The purpose of the present investigation was to determine the independent effects of hypoxia and physical exercise on peripheral cholecystokinin (CCK) metabolism in humans. Thirty-two physically active men were randomly assigned in a double-blind manner to either a normoxic (N; n = 14) or hypoxic (H; n = 18) group. During the acute study, subjects in the H group only participated in two tests, separated by 48 h, which involved a cycling test to exhaustion in normobaric normoxia and normobaric hypoxia (inspired O(2) fraction = 0.21 and 0.16, respectively). In the intermittent study, N and H groups cycle-trained for 4 wk at the same relative exercise intensity in both normoxia and hypoxia. Acute normoxic exercise consistently raised plasma CCK during both studies by 290-723%, which correlated with increases in the plasma ratio of free tryptophan to branched chain amino acids (r = 0.58-0.71, P < 0.05). In contrast, acute hypoxic exercise decreased CCK by 7.0 +/- 5.5 pmol/l, which correlated with the decrease in arterial oxygen saturation (r = 0.56, P < 0.05). In the intermittent study, plasma CCK response at rest and after normoxic exercise was not altered after physical training, despite a slight decrease in adiposity. We conclude that peripheral CCK metabolism 1) is more sensitive to acute changes than chronic changes in energy expenditure and 2) is potentially associated with acute changes in tissue PO(2) and metabolic precursors of cerebral serotoninergic activity. (+info)
Resistance exercise training reduces hypertriglyceridemia in HIV-infected men treated with antiviral therapy.
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Hypertriglyceridemia, peripheral insulin resistance, and trunk adiposity are metabolic complications recently recognized in people infected with human immunodeficiency virus (HIV) and treated with highly active antiretroviral therapy (HAART). These complications may respond favorably to exercise training. Using a paired design, we determined whether 16 wk of weight-lifting exercise increased muscle mass and strength and decreased fasting serum triglycerides and adipose tissue mass in 18 HIV-infected men. The resistance exercise regimen consisted of three upper and four lower body exercises done for 1-1.5 h/day, 4 days/wk for 64 sessions. Dual-energy X-ray absorptiometry indicated that exercise training increased whole body lean mass 1.4 kg (P = 0.005) but did not reduce adipose tissue mass (P = NS). Axial proton-magnetic resonance imaging indicated that thigh muscle cross-sectional area increased 5-7 cm(2) (P < 0.005). Muscle strength increased 23-38% (P < 0.0001) on all exercises. Fasting serum triglycerides were decreased at the end of training (281-204 mg/dl; P = 0.02). These findings imply that resistance exercise training-induced muscle hypertrophy may promote triglyceride clearance from the circulation of hypertriglyceridemic HIV-infected men treated with antiviral therapy. (+info)
Effect of oral creatine supplementation on human muscle GLUT4 protein content after immobilization.
(61/816)
The purpose of this study was to investigate the effect of oral creatine supplementation on muscle GLUT4 protein content and total creatine and glycogen content during muscle disuse and subsequent training. A double-blind placebo-controlled trial was performed with 22 young healthy volunteers. The right leg of each subject was immobilized using a cast for 2 weeks, after which subjects participated in a 10-week heavy resistance training program involving the knee-extensor muscles (three sessions per week). Half of the subjects received creatine monohydrate supplements (20 g daily during the immobilization period and 15 and 5 g daily during the first 3 and the last 7 weeks of rehabilitation training, respectively), whereas the other 11 subjects ingested placebo (maltodextrine). Muscle GLUT4 protein content and glycogen and total creatine concentrations were assayed in needle biopsy samples from the vastus lateralis muscle before and after immobilization and after 3 and 10 weeks of training. Immobilization decreased GLUT4 in the placebo group (-20%, P < 0.05), but not in the creatine group (+9% NS). Glycogen and total creatine were unchanged in both groups during the immobilization period. In the placebo group, during training, GLUT4 was normalized, and glycogen and total creatine were stable. Conversely, in the creatine group, GLUT4 increased by approximately 40% (P < 0.05) during rehabilitation. Muscle glycogen and total creatine levels were higher in the creatine group after 3 weeks of rehabilitation (P < 0.05), but not after 10 weeks of rehabilitation. We concluded that 1) oral creatine supplementation offsets the decline in muscle GLUT4 protein content that occurs during immobilization, and 2) oral creatine supplementation increases GLUT4 protein content during subsequent rehabilitation training in healthy subjects. (+info)
Protein metabolism during intensive physical training in the young adult.
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Two groups of men consumed two levels of protein (1.4 and 2.8 g/kg body weight) during a 40-day experimental period. Physical activity and the sweat rates were fairly high during the entire experimental phase. Urinary nitrogen excretions remained fairly constant for both groups during the training and heavy physical activity periods. Nitrogen balances were positive exclusive or inclusive of the daily sweat nitrogen losses showing nitrogen retention. The essentially unchanged blood hemoglobin and serum protein levels showed that the control group was receiving an adequate protein intake to maintain nitrogen equilibrium, under conditions of fairly heavy physical acitvity. Although others may have suggested some compensatory reductions in the urinary excretion of nitrogen under conditions of profuse sweating, our data have not supported these conclusions. It appears that sweat losses of nutrients become relevant in determining requirements and will increase in importance as sweat rates are increased. The data again demonstrate that the nutrient losses during profuse sweating consitute an error that could seriously invalidate the accuracy of metabolic balance studies. In this study, although the men did increase body protein stores and muscle mass with high-protein diets, the additional body protein did not enhance physiological work performance. It is suggested that in this sutdy 100 g of protein/day was adequate for men performing fairly heavy work. (+info)
Peak expiratory flow in youths with varying cigarette smoking habits.
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Measurements of peak expiratory flow (P.E.F.) were done on 195 boys arriving at a detention centre, and again eight weeks later at the time of their discharge. During this time they took much physical exercise, and cigarette smoking and drug taking were not permitted. At the initial assessment there was an impairment of P.E.F. inversely proportional to the amount of cigarettes smoked which was statistically significant. There was a significant improvement in P.E.F. between reception and discharge in all groups of boys with varying smoking habits, all groups except the heavy smokers achieving near normal results after eight weeks. The heavier smokers improved more than the non-smokers or light smokers, but this difference was not statistically significant. Suggested reasons for this improvement are discussed. (+info)
Influence of high intensity training on menstrual cycle disorders in athletes.
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AIM: To estimate the influence of intensive training on menstrual cycles in female athletes. METHOD: The questionnaire was used to determine the time of menarche, and the prevalence of primary and secondary amenorrhea and dysmenorrhea in 72 active female athletes from Zagreb (10 volleyball players, 18 basketball players, 10 ballet dancers, and 34 runners) aged between 15 and 21. The control group comprised 96 girls of the same age not engaged in any sports activity. RESULTS: The prevalence of secondary amenorrhea was three times higher in athletes than in the control group (p=0.037). The prevalence of primary amenorrhea was substantially higher in athletes than in the control group (6/72 vs. 0/96, p=0.014), whereas the prevalence of dysmenorrhea was twofold lower in athletes than in the control group (p<0.001). The highest prevalence of secondary amenorrhea was recorded in runners (14/31), particularly long-distance runners (11/17), whereas there was only one case of secondary amenorrhea among basketball players. Menarche was significantly delayed in the athletes who started physical activities before the onset of menstruation (13.8+1.4 vs. 12.6+1.0 years, p<0.001). CONCLUSION: High-intensity training before menarche postpones its onset. Type of training may be related to a significantly higher prevalence of secondary amenorrhea in runners than in basketball players. (+info)