Towards a better understanding of physical activity among children and adolescents
This dissertation included a series of papers involving physical activity among children and adolescents. The first study examined the predictive validity of an age-specific MET prediction equation among children of varying body size. The results indicated that a widely used MET prediction equation overestimates energy expenditure at slow walking speeds (except 1 mph). This overestimation was greater among relatively smaller children. Contemporary issues dealing with youth physical activity and energy expenditure levels were also examined in this dissertation. The day-to-day variability in estimated energy expenditure was examined using generalizability theory. The results suggested that limited variability in daily energy expenditure existed during a 7-day monitoring period. It was concluded that small daily absolute changes in the energy expended from sedentary, light, moderate, and vigorous activity existed to maintain levels of total energy expenditure. The largest source of variability in daily energy expenditure (other than the differences between intensity levels) was from the participant x activity intensity interaction term (23%). Traditionally, the inter-individual differences in physical activity or energy expenditure focus on age and gender differences. This dissertation also examined maturity-related differences in moderate-to-vigorous physical activity. Although significant differences in the average amount of MVPA/day were not found between biological maturity groups the absolute differences in MVPA were considered. Early maturing boys and late maturing girls averaged the most MVPA/day. Among boys, this observation may be related to somatic changes that occur during puberty. Among girls, underlying biological mechanisms may exist that reduce physical activity in early maturers to optimize reproductive potential;Although the focus in physical activity research is typically on the average amount of daily physical activity between groups, it is also important to understand the primary sources of daily physical activity. The final study of this dissertation quantified the relative contribution of youth sport to total daily physical activity. The results indicate that, on average, youth sport contributed nearly 25% of the total daily MVPA, which was equivalent to approximately 30 minutes. However, it appears that the additional MVPA accumulated during youth sport was not maintained on a non-youth sport day.