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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

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