Short-term muscle power during growth and maturation.

During growth and maturation, the study of very brief high-intensity exercise has not received the same attention from researchers as, for instance, aerobic function. In anaerobic tasks or sports events such as sprint cycling, jumping or running, the children's performance is distinctly lower than that of adults. This partly reflects children's lesser ability to generate mechanical energy from chemical energy sources during short-term intensive activity. For many years, various attempts have been made to quantify the anaerobic energy yield in maximal-intensity exercise, but many assumptions have had to be made with respect to mechanical efficiency, lactate turnover, dilution space for lactate, and so on. During childhood and adolescence, direct measurements of the rate or capacity of anaerobic pathways for energy turnover presents several ethical and methodological difficulties. Thus, rather than measure energy supply, paediatric exercise scientists have concentrated on measuring short-term muscle power (STMP) by means of standardised tests. Previously, investigators have used various protocols such as short-term cycling power tests, vertical jump tests or running tests. Cycling ergometer tests are the most common. There is, however, no ideal test, and so it is important to acknowledge the limitations of each test. Progress has been made in assessing instantaneous cycling STMP from a single exercise bout. Several investigators have reported STMP increases with age and have suggested that late pubertal period may accentuate anaerobic glycolysis. Mass-related STMP was shown to increase dramatically during childhood and adolescence, whereas the corresponding increase in peak blood lactate was considerably lower. The latter results support the hypothesis that the difference observed between children and adolescents during STMP testing is more related to neuromuscular factors, hormonal factors and improved motor coordination, rather than being an indicator of reduced lactate-producing glycolysis mechanism. Evidence suggesting a causal link between the ability to generate lactate during exercise and sexual maturation is weak. Despite the majority of research being focused on short-term power output, the study of anaerobic function warrants more investigation. Spectacular progress is being made at the moment in the development of molecular biology tools that can be used in, for example, the genetic dissection of human performance phenotypes. Noninvasive power tools like magnetic resonance imaging and magnetic resonance spectroscopy are presently used to determine possible differences in phosphorus compounds between fast and slow fibre types. Undoubtedly these tools will lead to more information in the near future regarding STMP capabilities of the growing child.