Results There was consistent evidence for a positive association between MF and physical activity .
For both MF components , there was support for objective ly measured physical activity , particularly for activity of vigorous intensity .
Sports participation was also consistently linked with both MF components , whereas the association with active transport was inconsistent .
For both MF components , associations with sedentary behaviors were inconsistent irrespective of measurement method , and the association between MF and sleep was considered uncertain .
Conclusions The available evidence supports a link between MF and physical activity , particularly for vigorous intensity activity and organized sports participation .
Background Muscular fitness ( MF ) is considered a powerful marker of health , but the extent to which common health behaviors are associated with MF during childhood and adolescence is currently unclear .
Objective We conducted a systematic review of studies investigating associations between MF ( i.e. , strength/power , local muscular endurance ) and physical activity , sedentary behaviors , and sleep in children and adolescents .
Changes in physical activity are reflected in changes in fitness during late adolescence. A 2-year follow-up study.
The study describe changes over 2 years in different physical fitness measures and the relationship between these changes and changes in physical activity . Maximal aerobic work capacity ( Wattmax ) , functional strength , muscle endurance , agility and flexibility were measured in 259 r and omly selected high school boys and girls 16.5 years of age and followed-up 2 years later , while they still attended school . Most physical fitness measures increased over time in boys , and in girls an increase was found in arm extensor strength and trunk extensor endurance , but Wattmax per kg body mass decreased . Changes in physical performance between 16 and 18 years of age seem to be very similar in different countries , despite differences in physical activity patterns and absolute level of performance . No change was found in time of participation in physical activity or sports activity  in either gender , but fewer girls participated in  leisure-time sports  at the 2nd test ( p < 0.001 ) . Change in physical activity or sports activity  did not relate to change in physical fitness level . The relationships between level of sports participation ( competition , for health or none ) and physical fitness measures at baseline and at the 2nd test were weak or non-significant . Three explanations for the weak relationship between physical activity and fitness are suggested : ( A ) part of the variability in fitness is explained by genetics , ( B ) growth and hormonal changes , especially in boys , override the stimulus of training , and ( C ) the physical fitness level in adolescents is so high that only physical activity at high relative intensity is supposed to have an effect on the fitness level
Results There was consistent evidence for a positive association between MF and physical activity .
For both MF components , there was support for objective ly measured physical activity , particularly for activity of vigorous intensity .
Sports participation was also consistently linked with both MF components , whereas the association with active transport was inconsistent .
For both MF components , associations with sedentary behaviors were inconsistent irrespective of measurement method , and the association between MF and sleep was considered uncertain .
Conclusions The available evidence supports a link between MF and physical activity , particularly for vigorous intensity activity and organized sports participation .
Background Muscular fitness ( MF ) is considered a powerful marker of health , but the extent to which common health behaviors are associated with MF during childhood and adolescence is currently unclear .
Objective We conducted a systematic review of studies investigating associations between MF ( i.e. , strength/power , local muscular endurance ) and physical activity , sedentary behaviors , and sleep in children and adolescents .