children and adolescents and other potential correlates. Several questions merit
consideration. What factors, biological, behavioral, and/or cultural, influence the
tracking of physical activity from childhood into adolescence and adulthood? What
is unique about those individuals in whom activity tracks compared to those in
whom activity does not track? What are the determinants of tracking and
non-tracking?
Issues related to sport participation need further study. Sport participation
declines with age and parallels the trend in physical activity. The decline probably
begins before adolescence and reflects differential dropout (voluntary and invol-
untary) and the selectivity of sport as focus shifts from the general population of
youth to the more elite (Malina 2009 , 2010 ). Yet, youth active in sport tend to be
more active than those not involved in sport. Among adolescent boys, for example,
an estimated 11–13% of total daily energy expenditure occurred in the context of
organized sports; these percentages corresponded to 35–42% of the daily MVPA
fraction of energy expenditure (Machado Rodrigues et al.2012b).
Pubertal Transition and Biological Maturation
Reviews of correlates of physical activity are limited by the protocols of studies
included. As such, they are limited by the age ranges within and across grades and
types of information gathered. The pubertal transition and early adolescence span
about 9–15 years. One review (Gustafson and Rhodes 2006 ) focused on parental
correlates in this age range. Parental support was a correlate of activity, but results
for the role of parental physical activity were mixed. Data for single-parent families,
ethnicity, and socioeconomic status were inconclusive.
The transition begins at about 9–10 years in girls and 11–12 years in boys,
although there is considerable inter-individual variability. Peak height velocity
(PHV) is attained, on average, at about 12.0 years in girls and 14.0 years in boys,
while menarche occurs, on average, after PHV (Malina et al. 2004 ). There is a need
to consider correlates of physical activity during the interval, including estimates of
maturity status and timing.
Briefly, maturity status refers to the level of maturation at the chronological age
of observation, and maturity timing refers to the chronological age at which specific
maturational events occur. Though related, the two are not equivalent (Malina et al.
2004 , 2015 ). Tempo or rate of maturation is a related aspect, but is difficult to
estimate. Commonly used indicators of maturity status in growth studies include
skeletal age, breast and pubic development in girls, genital and pubic hair devel-
opment in boys, testicular volume, and menarcheal status (i.e., menarche has or has
not been attained). Two indicators of maturity timing, age at peak height velocity
and age at menarche, require longitudinal observations that span adolescence. Age
at peak height velocity, the maximal rate of growth in height during the adolescent
growth spurt, is estimated from height measurements of individual children taken
annually or semiannually across adolescence. Age at menarche, thefirst menstrual
5 Physical Activity and Inactivity Among Children... 83