Effects of a 10-week conventional strength training program on lower leg muscle performance in adolescent boys compared to adults.

AIM: The use of resistance training by adolescents has been an area of controversy. The aim of the present work was therefore to evaluate the degree of strength trainability in adolescents compared to adults. METHODS: Thirteen healthy male adolescents (AL) and eight adults (AD) volunteered to participate in a 10-week training program. Subjects performed supervised exercises for the legs, calf raise, leg curl and leg extension three times a week. Maximal strength, explosive power and anaerobic power were assessed prior and after the 10-week training program. RESULTS: Significant interaction effects (time * age group) were found only for explosive strength as improvements of squat jump and counter movement jump performance (P<0.05) in favor of the AL group. No between-group changes were found for maximal strength and anaerobic power. However, significant time effects were observed for these parameters within both groups. CONCLUSION: Taken together, adolescents show distinct muscular adaptations by a higher gain in explosive power in response to resistance training when compared to adults. This might be related to peak height velocity (PHV) which is a "sensitive" period of trainability and accelerated adaptation to resistance training in adolescents.

Different metabolic responses during incremental exercise assessed by localized 31P MRS in sprint and endurance athletes and untrained individuals.

Until recently, assessment of muscle metabolism was only possible by invasive sampling. 31P magnetic resonance spectroscopy (31P MRS) offers a way to study muscle metabolism non-invasively. The aim of the present study was to use spatially-resolved 31P MRS to assess the metabolism of the quadriceps muscle in sprint-trained, endurance-trained and untrained individuals during exercise and recovery. 5 sprint-trained (STA), 5 endurance-trained (ETA) and 7 untrained individuals (UTI) completed one unlocalized 31P MRS session to measure phosphocreatine (PCr) recovery, and a second session in which spatially-resolved 31P MR spectra were obtained. PCr recovery time constant (τ) was significantly longer in STA (50±17 s) and UTI (41±9 s) than in ETA (30±4 s), (P<0.05). PCr changes during exercise differed between the groups, but were uniform across the different components of the quadriceps within each group. pH during recovery was higher for the ETA than for the UTI (P<0.05) and also higher than for the STA (P<0.01). Muscle volume was greater in STA than in UTI (P<0.05) but not different from ETA. Dynamic 31P MRS revealed considerable differences among endurance and sprint athletes and untrained people. This non-invasive method offers a way to quantify differences between individual muscles and muscle components in athletes compared to untrained individuals.