A Cochrane review included 16 studies with a total of 1191 subjects between 11 and 19 years of age.
In a general population of children, eleven trials compared vigorous exercise versus no intervention. Six studies reporting anxiety scores showed a non-significant trend in favour of the exercise group (standard mean difference (SMD) (random effects model) -0.48, 95%CI -0.97 to 0.01). Five studies reporting depression scores showed a statistically significant difference in favour of the exercise group (SMD (random effects model) -0.66, 95% CI -1.25 to -0.08). Five trials comparing vigorous exercise to low intensity exercise showed no statistically significant difference in depression (2 trials, SMD-0.15, 95% CI -0.44 to 0.14) and anxiety (3 trials, SMD -0.14, 95% CI -0.41 to 0.13) scores. Exercise compared with psychosocial interventions showed no difference in depression (2 trials, SMD 0.10, 95% CI-0.21 to 0.41) or anxiety scores (2 trials, SMD -0.13, 95% CI -0.43 to 0.17).
In children in treatment, one small trial comparing vigorous exercise versus no intervention showed no statistically significant difference in depression scores (SMD (fixed effects model) 0.78, 95% CI -0.47 to 2.04). No studies reported anxiety scores. Two small trials comparing vigorous exercise to low intensity exercise found no difference in depression scores for children in treatment (SMD -0.31, 95% CI -0.78 to 0.16). One trial comparing exercise with psychosocial interventions found no difference in depression scores for children in treatment (SMD -0.31, 95% CI -0.97 to 0.35).
Comment: The evidence is downgraded by sparse data, especially considering children in treatment, and inconsistency. All trials were generally of low methodological quality.