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flow, is obtained for individual girls followed prospectively at relatively short


intervals during adolescence (3–6 months, though annually in some studies). Girls


and/or their mothers are interviewed whether or not menarche has occurred; if it


occurred, further questions pinpoint the time/age. The prospective method should


not be confused with the status quo and retrospective methods for obtaining age at


menarche (see Malina et al. 2004 , 2015 ).


Inter-individual variation in biological maturation has been increasingly noted as


a factor that may contribute to physical activity during childhood (Eaton and Yu


1989 ) and especially during adolescence (Cumming et al. 2008 , 2012b, 2014 ;


Machado Rodrigues et al. 2010 ; Sherar et al. 2007 ; Thompson et al. 2003 ).


Although boys are, on average, more physically active than girls, the sex difference


is attenuated when maturity timing or status is controlled (Thompson et al. 2003 ;


Machado Rodrigues et al. 2010 ). By inference, early adolescent girls tend to be less


active and more sedentary than boys of the same age due to their advanced bio-


logical maturation.


The influence of biological maturation on physical activity may be direct or


indirect. Direct effects reflect changes in activity attributable to biology. Active


play, for example, is considered as a biologically driven and time-sensitive behavior


whose primary purpose is to support the development and maturation of the central


nervous system (Byers 1998 ; Byers and Walker 1995 ). With maturation of the
nervous system, active play becomes biologically redundant resulting in a reduced


drive to engage in active play behavior. This explains why active play declines in


adolescence, even among youth who remain physically active during this phase of


development (Cumming et al. 2014 ; Payne et al. 2013 ). It also explains why


reductions in active play occur earlier in girls due to their advanced maturation


compared to boys.


Indirect effects of inter-individual variation in maturation on physical activity are


mediated by beliefs, self-perceptions, social interactions, and social expectations;


evaluations and reactions of others; and also more subtle societal and cultural


factors (Cumming et al.2012a, 2014 ; Pindus et al. 2014 ; Sherar et al. 2009 , 2010 ).


Physical self-concept, for example, has consistently been shown to mediate an


inverse relation between maturation and physical activity in adolescent females,


with early maturing girls perceiving themselves as less attractive, less competent at


sports, and less physicallyfit (Cumming et al. 2008 ; Hunter Smart et al. 2012 ;


Jackson et al. 2013 ).


The preceding discussion of physical activity also applies to sport, a highly


valued context of physical activity among youth. Sport shows sport-specific


selectivity that often starts during the transition and continues through adolescence.


Selectivity tends to follow size and maturity-related gradients evident in data for


skeletal age and secondary sex characteristics of youth athletes in many sports


(Malina 2002 , 2011 ; Malina et al. 2013 ). Note that the sport environments of youth


are typically regulated by adults who can influence the experiences of participants


both directly and indirectly. Poor coaching and instruction are among the more


common reasons youth note as a reason for leaving sport. Although youth can


84 R.M. Malina et al.

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