This review included 24 studies (n=39,512): five experimental studies; six quasi-experimental (no control group); and 13 observational studies. Sample size ranged from 55 to 11,887 people. Five studies exclusively included adolescents (10 to 19 years)
Study quality: Average quality scores were 17.2 (range 14 to 21) out of 28 for experimental studies and 16.4 (range 12 to 19) out of 24 for observational studies. Common methodological flaws included lack of clear description of confounders, lack of blinding and lack of use of valid and reliable outcome measures.
Experimental and quasi-experimental studies: All studies showed favourable effects of physical intervention on adiposity level. One study showed decreased obesity among girls only; all other experimental studies showed comparable results between boys and girls.
Observational studies: All except two studies showed significant inverse associations of physical activity with body composition or body mass index. Some studies reported that these outcomes depended on sex, ethnicity and baseline body mass index. Observational studies demonstrated that physical activity may play a role in the prevention of fat accumulation in normal-weight participants, although most studies estimated physical activity from questionnaires where there were several differences between units of measurement, cut-off points and type of physical activity.