ABSTRACT
Physical activity (PA) and aerobic fitness are often used interchangeably but they are not synonymous. The issue is confused further by lack of clarity in their assessment and interpretation in relation to health and well-being. To clarify the development and relationship between PA and aerobic fitness and to examine young people’s current habitual PA (HPA) and aerobic fitness (peak V̇O2) with reference to earlier generations. A minority of young people and more boys than girls meet current PA guidelines. HPA declines with age. Boys achieve higher peak V̇O2 values than girls from an early age and in both sexes there is a progressive rise in peak V̇O2 with age and maturation independent of the influence of body mass. There is no compelling evidence that young people have low levels of peak V̇O2 or that either HPA or peak V̇O2 have decreased over time. Exercise training can enhance the peak V̇O2 of both children and adolescents but a meaningful relationship between HPA and peak V̇O2 remains to be proven. Progress in understanding youth health requires researchers to rigorously explain and justify the behaviours and physiological variable(s) investigated, particularly when using them in subsequent statistical analyses with health-related variables.
