Although skeletal muscle is capable of oxidizing selected amino acids, exercise in the fed and carbohydrate-replete condition results in only a small increase in amino acid utilization. Nevertheless, it may be important to increase the dietary protein requirements of active individuals. There is ongoing debate as to whether the amino acids for oxidation are derived from the free amino acid pool, from net protein breakdown, or a combination of both. There has been interest in the potential ergogenic benefits of amino acid ingestion; however, BCAA ingestion does not appear to affect fatigue during prolonged exercise, there is little support from controlled studies to recommend glutamine ingestion for enhanced immune function, and although glutamine stimulates muscle glycogen synthesis, its addition to carbohydrate supplements provides no additional benefit over ingestion of carbohydrate alone.
Mark Hargreaves and Rodney Snow
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.
Kim Bennell, Karim Khan, Bernadette Matthews, Elizabeth Cook, Karen Holzer, Heather McKay and John Wark
It is not clear at what age or maturational stage physical activity is most effective in optimizing peak bone mass in girls. We compared bone mineral of 78 pre- and early-pubertal novice female ballet dancers (mean age, 9.6 years, SD, 0.8) with that of 52 age-matched controls. Dancers had 4.5% greater total hip bone mineral density (BMD) and 4.9% greater femoral neck BMD (both p < .01) than controls. BMD at the lumbar spine and upper and lower limbs was similar between groups. These findings could not be explained by maturity, size, body composition, or dietary calcium intake differences between groups. While genetics may partially explain these findings, we propose that the mechanical loading of dance training provided appropriate skeletal stimulus to generate site-specific BMD advantage.
Jill N. Schulte and Kevin E. Yarasheski
Advancing age is associated with a reduction in skeletal muscle protein, muscle strength, muscle quality, and chemical modifications that may impair protein function. Sarcopenia has been coupled with physical disability, frailty, and a loss of independent function (5, 19). Using stable isotope tracer methodologies and mass spectrometric detection, we observed: (a) 76–92-year-old physically frail and 62–74-year-old middle-age adults have lower mixed muscle protein synthetic rates than 20–32-year-old men and women; (b) 2 weeks and 3 months of weightlifting exercise increased the synthetic rate of myosin heavy chain (MHC) and mixed muscle proteins to a similar magnitude in frail, middle-age, and young women and men; (c) Serum myostatin-immunoreactive protein levels were elevated in physically frail women and were inversely correlated with lean mass. This suggests that the protein synthetic machinery adapts rapidly to increased contractile activity and that the adaptive response(s) are maintained even in frail elders.
Susan K. Grimston and Ronald F. Zernicke
Physical exercise is touted as being beneficial for enhancing the functional quality of the skeletal system, as well as the cardiovascular and muscular systems. Unwise training practices, however, combined with potential risk factors may dispose an individual to a bone stress reaction (bone responses to repetitive loads within the physiological range) or stress fracture (frank fracture of a bone from clinically significant stress reactions that produce structural failure). Here, we trace the terms that have been used to describe these injuries and recount the etiology of stress reactions and fractures. Epidemiological data have been reported for military and athletic populations, and in many instances recurring risk factors have been identified, both those that can be modified and those that cannot. In this paper, we review epidemiological data and potential risk factors for stress fractures and summarize current thought about the treatment and prevention of these exercise-related injuries.
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.
Arnel L. Aguinaldo, Janet Buttermore and Henry Chambers
High rotational torques during baseball pitching are believed to be linked to most overuse injuries at the shoulder. This study investigated the effects of trunk rotation on shoulder rotational torques during pitching. A total of 38 pitchers from the professional, college, high school, and youth ranks were recruited for motion analysis. Professional pitchers demonstrated the least amount of rotational torque (p = .001) among skeletally mature players, while exhibiting the ability to rotate their trunks significantly later in the pitching cycle, as compared to other groups (p = .01). It was concluded that the timing of their rotation was optimized as to allow the throwing shoulder to move with decreased joint loading by conserving the momentum generated by the trunk. These results suggest that a specific pattern in throwing can be utilized to increase the efficiency of the pitch, which would allow a player to improve performance with decreased risk of overuse injury.
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.
Eleni Michopoulou, Alexandra Avloniti, Antonios Kambas, Diamanda Leontsini, Maria Michalopoulou, Symeon Tournis and Ioannis G. Fatouros
This study determined dietary intake and energy balance of elite premenarcheal rhythmic gymnasts during their preseason training. Forty rhythmic gymnasts and 40 sedentary age-matched females (10–12 yrs) participated in the study. Anthropometric profile and skeletal ages were determined. Dietary intake and physical activity were assessed to estimate daily energy intake, daily energy expenditure, and resting metabolic rate. Groups demonstrated comparable height, bone age, pubertal development, resting metabolic rate. Gymnasts had lower body mass, BMI, body fat than age-matched controls. Although groups demonstrated comparable daily energy intake, gymnasts exhibited a higher daily energy expenditure resulting in a daily energy deficit. Gymnasts also had higher carbohydrate intake but lower fat and calcium intake. Both groups were below the recommended dietary allowances for fiber, water, calcium, phosphorus and vitamin intake. Gymnasts may need to raise their daily energy intake to avoid the energy deficit during periods of intense training.
Koichi Nakazato, Tatsuro Hirose and Hongsun Song
More than 15% dietary protein has reportedly not led to significant muscle hypertrophy in normal growing rats. The aim of this study was to test whether a high protein (HP) diet affects myostatin (Mstn) synthesis in a rat gastrocnemius muscle. Twenty-four male Wistar rats (4-wk-old) were divided into three groups: 1) control diet (15% protein; 15P, n = 8), 2) the 25P group (25% protein, n = 8), and 3) the 35P group (35% protein, n = 8). After 3 wk of isoenergetic feedings, the Mstn level in skeletal muscles was determined using Northern and Western blotting analysis. After the experimental feeding, muscle masses were similar among groups. The 35P showed significant high expressions of Mstn both at mRNA and protein levels. Obtained results suggest that a high-protein diet leads to the high Mstn level to restrict muscle hypertrophy.