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Han C.G. Kemper, G. Bertheke Post and Jos W.R. Twisk

This longitudinal study evaluates the relationship of food intake and physical activity with biological maturation of 200 boys and girls during adolescence and young adulthood. The subjects were followed during 9 years from ages 12 to 22 years, with repeated measurements at ages 13, 14, 15, 16, and 21. Biological maturation was estimated four times between ages 12 and 17 as skeletal age by radiographs of the left hand and wrist. Daily nutritional intake (macro- and micronutrients) was assessed with a cross-checked dietary history method. Daily physical activity was assessed through structured interview, whereby average weekly time spent in activity was used to assign a weighted activity score. The 107 girls and 93 boys were divided into three maturity groups: early maturers, late maturers, and average maturers. It was concluded that in both sexes, late maturation seemed to coincide with a higher energetic food intake and a slightly higher activity pattern than early maturation during adolescence.

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Sharon Ann Plowman

This paper describes the effects of exercise training on the somatic, skeletal, and sexual maturation of children. Young athletes of both sexes grow at the same rate and to the same extent as young nonathletes. However, there is evidence that the pubertal development of young female athletes may be delayed. Menarche is more consistently late than either thelarche or pubarche. Genetic and environmental factors are explored in an attempt to determine causative mechanisms. Longitudinal training data are needed for both boys and girls on a variety of physical and hormonal variables. Until such data are available, it is recommended that all children engage in regular physical activity but that maturational progress be monitored in those involved in strenuous competitive training.

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Anni Rava, Anu Pihlak, Jaan Ereline, Helena Gapeyeva, Tatjana Kums, Priit Purge, Jaak Jürimäe and Mati Pääsuke

The purpose of this study was to evaluate the differences in body composition, neuromuscular performance, and mobility in healthy, regularly exercising and inactive older women, and examine the relationship between skeletal muscle indices and mobility. Overall, 32 healthy older women participated. They were divided into groups according to their physical activity history as regularly exercising (n = 22) and inactive (n = 10) women. Body composition, hand grip strength, leg extensor muscle strength, rapid force development, power output, and mobility indices were assessed. Regularly exercising women had lower fat mass and higher values for leg extensor muscle strength and muscle quality, and also for mobility. Leg extensor muscle strength and power output during vertical jumping and appendicular lean mass per unit of body mass were associated with mobility in healthy older women. It was concluded that long-term regular exercising may have beneficial effects on body composition and physical function in older women.

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Mark R. Forwood

Experiments to design physical activity programs that optimize their osteogenic potential are difficult to accomplish in humans. The aim of this article is to review the contributions that animal studies have made to knowledge of the loading conditions that are osteogenic to the skeleton during growth, as well as to consider to what extent animal studies fail to provide valid models of physical activity and skeletal maturation. Controlled loading studies demonstrate that static loads are ineffective, and that bone formation is threshold driven and dependent on strain rate, amplitude, and duration of loading. Only a few loading cycles per session are required, and distributed bouts are more osteogenic than sessions of long duration. Finally, animal models fail to inform us of the most appropriate ways to account for the variations in biological maturation that occur in our studies of children and adolescents, requiring the use of techniques for studying human growth and development.

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Mitchell M. Kanter and Melvin H. Williams

Three nutritional products that have very different mechanisms of action are antioxidant vitamins, carnitine, and choline. Antioxidant vitamins do not appear to have a direct effect on physical performance in well-fed people but have been touted for their ability to detoxify potentially damaging free radicals produced during exercise. Carnitine purportedly enhances lipid oxidation, increases VO2max, and decreases plasma lactate accumulation during exercise. However, studies of carnitine do not generally support its use for ergogenic purposes. Choline supplements have been advocated as a means of preventing the decline in acetylcholine production purported to occur during exercise; this decline may reduce the transmission of contraction-generating impulses across the skeletal muscle, an effect that could impair one’s ability to perform muscular work. However, there are no definitive studies in humans that justify choline supplementation. Much of the scientific data regarding the aforementioned nutrients are equivocal and contradictory. Their potential efficacy for improving physical performance remains largely theoretical.

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Daniel Courteix, Christelle Jaffré, Philippe Obert and Laurent Benhamou

The aim of this study was to assess the effects of vigorous activity on the somatic and skeletal growths in young females reaching puberty. From a group of 41 prepubertal girls, 24 remained in this study: 10 gymnasts training 15 to 22 hr a week and 14 non-exercising controls. At the start and during the study period, bone age, height, weight, fat and lean mass were significantly lower in the gymnasts vs. the controls (p < .05). These variables had increased in the same way for both groups. At each investigation, the gymnasts had significantly higher BMC, BMD, and BMAD at all the sites (p < .01) except the whole body. The strong correlation between somatic measurements at the start and at the end of the study indicated that physical exercise does not disrupt the normal growth in these children.

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Daniel A. Galvão, Robert U. Newton and Dennis R. Taaffe

Resistance training has been shown to be the most effective exercise mode to induce anabolic adaptations in older men and women. Advances in imaging techniques and histochemistry have increased the ability to detect such changes, confirming the high level of adaptability that remains in aging skeletal muscle. This brief review presents a summary of the resistance-training studies that directly compare chronic anabolic responses to training in older (>60 years) men and women. Sixteen studies are summarized, most of which indicate similar relative anabolic responses between older men and women after resistance training. Relatively small sample sizes in most of the interventions limited their ability to detect significant sex differences and should be considered when interpreting these studies. Future research should incorporate larger sample sizes with multiple measurement time points for anabolic responses.

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Bareket Falk, Sarah Braid, Michael Moore, Deborah O’Leary, Phil Sullivan and Panagiota Klentrou

The objective of this study was to assess bone strength using quantitative ultrasound (QUS, Sunlight Omnisense) in pre- and early-pubertal normal weight (NW, % body fat ≤20, n = 28), and overweight (OW, % body fat ≥25, n = 15) boys. Groups were similar in chronological and skeletal age, sexual maturity, sports participation, and calcium intake. Leisure-time physical activity was lower in OW boys. Radial speed of sound (SOS) was similar in the two groups. Tibial SOS, however, was significantly lower in OW compared with NW (3,554 ± 109 vs. 3,646 ± 71 m·s−1, respectively). Among pre- and early-pubertal boys, higher adiposity appears to be associated with lower bone SOS in the lower extremities.

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Dennis J. Caine

This literature review reveals an accumulating body of evidence indicating that growth disturbance associated with both chronic and acute growth plate injury occurs in young athletes and may be more prevalent than formerly believed. Skeletal complications resulting from these injuries may include progressive bone shortening, progressive deformity, joint incongruity, and arthritic sequelae. Against this background an increased concern for the welfare of young athletes is recommended. It is emphasized that back pain or pain around a joint in young athletes may be the symptom of significant growth plate changes that require accurate diagnosis, adequate treatment, and specific recommendations about return to activity. Suggestions are given for further research and prevention of growth plate injuries.

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G. Lynis Dohm

We previously reported that insulin resistance in skeletal muscle of obese individuals was associated with decreases in insulin signal transduction and tyrosine kinase activity of the insulin receptor. Herein is reviewed the recently published data supporting the hypothesis that protein kinase C (PKC) phosphorylates the insulin receptor on serine/threonine residues to decrease tyrosine kinase activity and cause insulin resistance. Treatment of insulin receptors from obese subjects with alkaline phosphatase restored tyrosine kinase activity, suggesting that the reduced activity was a result of hyperphosphorylation of the receptor. Incubating human muscle fiber strips with PKC inhibitors restored insulin action in muscle of obese patients, while activating PKC with a phorbol ester caused insulin resistance in muscle from lean control patients. The beta isoform of PKC was elevated in muscle of obese, insulin-resistant patients. These data are consistent with the hypothesis that elevated PKC activity may cause insulin resistance by phosphorylating the insulin receptor to decrease tyrosine kinase activity.