Six-year longitudinal analysis shows physical activity impacts on lean mass development in adolescence

The study of physical activity effects on muscle and bone in youth are largely limited to cross-sectional comparisons among athletic and non-athletic groups and short-term intervention studies often less than one year. Critical to the field is the impact of physical activity throughout the developmental years on musculo-skeletal system and especially muscle and bone mass. With the development of a healthy muscle and bone mass, children will be better protected from the chronic diseases of osteoporosis and sarcopenia in middle and old ages. Unique to the literature is the longitudinal study design of body composition in the development years by Bailey et al (1). The research design and findings of the study by Baxter-Jones et al (in this issue) is one cohort from a series of studies from the University of Saskatchewan. In assessing lean mass development for 6 continuous years in a relatively large sample of boys and girls, the authors were able to provide estimates of lean mass development over a ten-year period. Further, because of their estimates of biological age as estimated from peak height velocity, the usual confounders of maturation and statue with lean mass development were taken into account. These adjustments are essential because of the effect of physical activity on maturation. Finally, because physical activity was assessed each year ove