Skeletal muscle proteins are constantly being synthesized and degraded, and the net balance between synthesis and degradation determines the resultant muscle mass. Biochemical pathways that control protein synthesis are complex, and the following must be considered: gene transcription, mRNA splicing, and transport to the cytoplasm; specific amino acyl-tRNA, messenger (mRNA), ribosomal (rRNA) availability; amino acid availability within the cell; the hormonal milieu; rates of mRNA translation; packaging in vesicles for some types of proteins; and post-translational processing such as glycation and phosphorylation/dephosphorylation. Each of these processes is responsive to the need for greater or lesser production of new proteins, and many states such as sepsis, uncontrolled diabetes, prolonged bed-rest, aging, chronic alcohol treatment, and starvation cause marked reductions in rates of skeletal muscle protein synthesis. In contrast, acute and chronic resistance exercise cause elevations in rates of muscle protein synthesis above rates found in nondiseased rested organisms, which are normally fed. Resistance exercise may be unique in this capacity. This chapter focuses on studies that have used exercise to elucidate mechanisms that explain elevations in rates of protein synthesis. Very few studies have investigated the effects of aging on these mechanisms; however, the literature that is available is reviewed.
Olga N. Fedotovskaya, Leysan J. Mustafina, Daniil V. Popov, Olga L. Vinogradova and Ildus I. Ahmetov
In red skeletal muscle, monocarboxylate transporter 1 (MCT1) is required for lactate to enter the myocytes for oxidation. The A1470T polymorphism (rs1049434) in the MCT1 gene was shown to be associated with lactate transport rates in human skeletal muscles. The aim of the study was to compare genotype and allele frequencies of the MCT1 gene polymorphism in 323 Russian athletes and 467 nonathletic controls and to investigate the association of the MCT1 gene A1470T polymorphism with maximal oxygen consumption and maximal lactate concentration in rowers (n = 79).
Genotyping for the A1470T MCT1 polymorphism was performed by PCR-RFLP method. Physiological measurements of 79 Russian rowers of national competitive standard were determined during an incremental test to exhaustion on a rowing ergometer.
Frequencies of the A allele (71.8% vs 62.5%, P < .0001) and AA genotype (59.8% vs 39.4%, P < .0001) were significantly higher in endurance-oriented athletes (n = 142) than in the control group. Mean blood lactate concentration was higher in male rowers with the T allele (AT+TT 10.26 ± 1.89 mmol/L, AA 8.75 ± 1.69 mmol/L, P = .005).
MCT1 gene A1470T polymorphism is associated with endurance athlete status and blood lactate level after intensive exercise.
Ronald L. Terjung, Ryszard Zarzeczny and H.T. Yang
Skeletal muscle mitochondrial capacity (mito), tissue blood flow (BF) capacity, and oxygen exchange capacity (e.g., DO2) appear to be well matched. The different skeletal muscle fiber types and muscle remodeled, due to inactivity >(e.g., related to aging or disease) or exercise training, exhibit widely differing aerobics capacities (V̇O2max). Yet, there are remarkably coordinated alterations in these 3 parameters in each of these conditions. With such a balance, there is likely shared control among these parameters in limiting (V̇O2max) of muscle, although this is a matter of considerable debate. The reduction in aerobic capacity in elderly can be improved by submaximal aerobic exercise training; this is related to increases in muscle mitochondria concentration and capillarity, but probably not BF capacity, as this is limited by central cardiovascular function. Thus, exercise-induced biochemical adaptations and angiogenesis occur in the elderly. The increase in muscle capillarity likely contributes to the increased oxygen exchange capacity, typical of endurance type training. The increase in [mito] appears essential to realize the increased in muscle V̇O2max with training and amplifies the rate-limiting influence of the muscle’s oxygen exchange capacity. Further, vascular remodeling induced by exercise in the elderly could be effective at improving flow capacity, if limited by peripheral obstruction. Thus, the limits to aerobic function specific to aged muscle appear most influenced by inactivity, whereas central cardiovascular changes impact whole body performance. Some may consider the aged myocyte as a small, inactive, normal myocyte in need of activity!
Dorina Ianc, Carmen Serbescu, Marius Bembea, Laurent Benhamou, Eric Lespessailles and Daniel Courteix
We investigated the effects of calcium supplementation and physical practice on the bone ultrasound properties and trabecular microarchitecture in children. 160 children aged 8−11 were randomly allocated to active or nonactive groups and to receive either a calcium-phosphate or a placebo powder for 6 months. Skeletal status was assessed using an ultrasound technique, which measures the speed of sound (Ad-SoS, m/s) at the phalanx. Bone microarchitecture was characterized by fractal analysis measured on calcaneus radiographs and the result expressed as the Hmean parameter, that has been shown to a good reliability of the bone texture quality. After 6 months, the calcium group had significantly gained Ad-SoS compared to the placebo group (P = 0.01) and Hmean increase was greater in the active than the nonactive group (P < 0.05). Exercise and calcium supplementation had a differential effect on the bone tissue, calcium being rather linked to a systemic effect whereas exercise has acted better onto the skeletal stressed site.
Erik A. Richter, Jørgen F.P. Wojtaszewski, Søren Kristiansen, Jens R. Daugaard, Jakob N. Nielsen, Wim Derave and Bente Kiens
In the present short review some factors affecting glucose utilization during exercise in skeletal muscle will be briefly described. Special focus will be put on the glucose transport step across the sarcolemma. Glucose transporters (GLUT4) are expressed at a surprisingly similar level in the different muscle fiber types in human skeletal muscle in contrast to findings in the rat. When working at the same absolute work load muscle glucose transport is decreased in trained compared with untrained muscle in part due to a decrease in GLUT4 translocation to the sarcolemma in trained muscle. However, when trained and untrained muscle are stressed severely by a workload taxing 100% of their peak oxygen uptake in a glycogen-depleted state, then glucose uptake is larger in trained than in untrained muscle and correlates with muscle GLUT4 content. Finally, the possible role of the AMP-activated protein kinase (AMPK) in regulating glucose uptake during exercise is discussed. It is indicated that at present no experiments definitively link activation of AMPK to activation of muscle glucose transport during exercise.
João Valente-dos-Santos, Manuel J. Coelho-e-Silva, Filipe Simões, Antonio J. Figueiredo, Neiva Leite, Marije T. Elferink-Gemser, Robert M. Malina and Lauren Sherar
This study evaluates the contributions of age, growth, skeletal maturation, playing position and training to longitudinal changes in functional and skill performance in male youth soccer. Players were annually followed over 5 years (n = 83, 4.4 measurements per player). Composite scores for functional and skill domains were calculated to provide an overall estimate of performance. Players were also classified by maturity status and playing position at baseline. After testing for multicollinearity, two-level multilevel (longitudinal) regression models were obtained for functional and skill composite scores. The scores improved with age and training. Body mass was an additional predictor in both models [functional (late maturing): 13.48 + 1.05 × centered on chronological age (CA)—0.01 × centered CA2—0.19 × fat mass (FM) + 0.004 × annual volume training—1.04 × dribbling speed; skills (defenders): 7.62 + 0.62 × centered CA—0.06 × centered CA2 + 0.04 × fat-free mass—0.03 × FM + 0.005 × annual volume training—0.19 × repeated-sprint ability + 0.02 × aerobic endurance]. Skeletal maturity status was a significant predictor of functional capacities and playing position of skill performance. Sound accuracy of each multilevel model was demonstrated on an independent cross-sectional sample (n = 52).
Gillian K. Myburgh, Sean P. Cumming, Manuel Coelho E. Silva, Karl Cooke and Robert M. Malina
To evaluate relationships among skeletal maturity, body size, and functional capacities of elite junior tennis players.
Participants were 88 elite British Junior tennis players (44 male; 44 female), 8–16 years of age (12.4 } 1.9 years). Skeletal age estimated maturty. Anthropometry, grip strength, countermovement jump, squat jump, forehand agility, backhand agility, Yo-Yo, 5-m, 10-m and 20-m sprints were measured. Comparative analysis for each sex was performed, relating advanced maturers (Male: 15; Female: 29) to a combination of on-time and late maturers (Male: 29; Female: 31). ANCOVAs were used to determine absolute differences between male and female players and between the 2 maturity subgroups, with chronological age as the covariate.
Advanced maturity afforded male players advantages in absolute measures of grip strength, speed, upper and lower body power but not in acceleration, agility or aerobic endurance. Male players were significantly taller than females in the U13-U16 age group. Advanced maturity in female players afforded advantages in absolute measures of grip strength, agility and overhead power, but not in backhand agility, aerobic endurance or squat jump power.
It is important that talent identification protocols consider the maturity of youth athletes to more satisfactorily address athletic potential rather than transient physical capabilities.
Over the past 3 decades, there has been a continued increase in the number of “older” participants in sporting events such as running, swimming, cycling, rowing, and weightlifting. Some master athletes come from a background with years of training and competition experience, while others have only begun to compete as they approach middle-aged and older. The majority of what we currently know about master athletes and aging has been gained from both cross-sectional and longitudinal testing and re-testing master athletes and recreational athletes. The focus of this paper is on the physiological profile of athletes and individuals performing regular exercise training. Physiological data from elite and non-elite, recreational, sedentary, and senior athletes clearly indicate that human skeletal muscle has a high degree of plasticity that is maintained late into life. Muscle fiber protein expression and single muscle fiber contractile properties are greatly influenced by exercise training. It appears that skeletal muscle can quickly adapt to accommodate a wide range of functionality to meet the demands (or lack of demands) placed upon it.
Adrienne J. McNamara, Michael J. Pavol and Katherine B. Gunter
Community-based exercise programs are popular for achieving physical activity among older adults, but the amount of physical activity obtained through such programs is unknown. This study quantified the bone-loading forces and levels of cardiovascular activity associated with participation in “Better Bones and Balance” (BBB), a community-based fall- and fracture-prevention program for older adults.
Thirty-six postmenopausal women age 73.2 ± 7.6 yr engages in BBB participated in this study. Ground-reaction forces (GRFs) associated with BBB exercises were evaluated using a force platform. Session and weekly totals of minutes of moderate to vigorous physical activity (MVPA) and total time spent above 55% maximum heart rate (HR) were measured using accelerometers and HR monitors, respectively.
BBB exercises produced mean 1-leg GRFs of 1.4–2.2 units body weight. Weekly BBB participation was associated with 126 ± 31 min of MVPA.
Activity obtained by BBB participation meets recommended guidelines for skeletal and cardiovascular health.
Sheila Muldoon, Rolf Bunger, Patricia Deuster and Nyamkhishig Sambuughin
This commentary discusses known links between Exertional Heat Illness (EHI), Malignant Hyperthermia (MH), and other hereditary diseases of muscle. Genetic and functional testing is also evaluated as measures of fitness to return to duty/play.
Reviews and research articles from Sports Medicine, Applied Physiology, and Anesthesiology.
Detailed comparisons of existing literature regarding clinical cases of EHI and MH and the potential utility of genetic testing, specifically the ryanodine receptor (RYR1) gene and other genes related to disorders of skeletal muscle.
EHI is a complex disorder wherein physiological, environmental, and hereditary factors interact to endanger an individual’s ability to maintain thermal homeostasis.
Individuals’ genetic background is likely to play an important role, particularly when EHI recurs. Recurrent EHI has been associated with MH and other genetic disorders, highlighting the importance of identification and exclusion of individuals with known high risk factors.