Results Physical activity was associated with numerous health benefits .
The dose-response relations observed in observational studies indicate that the more physical activity , the greater the health benefit .
Results from experimental studies indicate that even modest amounts of physical activity can have health benefits in high-risk youngsters ( e.g. , obese ) .
Vigorous intensity activities may provide even greater benefit .
Aerobic-based activities had the greatest health benefit , other than for bone health , in which case high-impact weight bearing activities were required .
Some of the health benefits can be achieved through an average of 30 minutes per day . [
Level 2 , Grade A ] .
Background The purpose was to : 1 ) perform a systematic review of studies examining the relation between physical activity , fitness , and health in school-aged children and youth , and 2 ) make recommendations based on the findings .
Resistance training and bone mineral density in adolescent females.
OBJECTIVE To examine the effects of 15 months of resistance training on bone mineral density ( BMD ) in female adolescents ( aged 14 to 17 years ) . STUDY DESIGN Participants were r and omly assigned to either a training ( n = 46 ) or control group ( n = 21 ) .  BMD and body composition were measured by using dual-energy x-ray absorptiometry . Strength was assessed by means of one-repetition maximums for the leg press and bench press . The exercise group trained 30 to 45 minutes a day , 3 days per week , using 15 different resistance exercises . Control participants remained sedentary ( < 2 hours of exercise per week ) . RESULTS Leg strength increased significantly ( 40 % ) in the exercise group , but there were no changes in the control group . Femoral neck BMD increased significantly in the training group ( 1.035 to 1.073 g/cm(2 ) , P < .01 ) but not in the control group ( 1.034 to 1.048 g/cm(2 ) ) . No significant changes were seen in either group in lumbar spine BMD ( 1.113 to 1.142 g/cm(2 ) and 1.158 to 1.190 g/cm(2 ) , respectively ) or total body BMD ( 1.103 to 1.134 g/cm(2 ) and 1.111 to 1.129 g/cm(2 ) , respectively ) . CONCLUSION Resistance training is a potential method for increasing bone density in adolescents , although such a program would be best done as part of the school curriculum
Results Physical activity was associated with numerous health benefits .
The dose-response relations observed in observational studies indicate that the more physical activity , the greater the health benefit .
Results from experimental studies indicate that even modest amounts of physical activity can have health benefits in high-risk youngsters ( e.g. , obese ) .
Vigorous intensity activities may provide even greater benefit .
Aerobic-based activities had the greatest health benefit , other than for bone health , in which case high-impact weight bearing activities were required .
Some of the health benefits can be achieved through an average of 30 minutes per day . [
Level 2 , Grade A ] .
Background The purpose was to : 1 ) perform a systematic review of studies examining the relation between physical activity , fitness , and health in school-aged children and youth , and 2 ) make recommendations based on the findings .