Previously, two systematic reviews reported that exercise had small to moderate beneficial effects in reducing the symptoms of depression. However, both of these reviews noted that most studies included small sample sizes and were of low methodological quality, limiting the value of any potential conclusions about the benefits of exercise for mental health in this age group. But research into exercise is bound to involve a few repetitions, so another systematic review was conducted involving much of the same evidence (Carter et al, 2016). In addition, an attempt to combine the existing evidence in a meta-analysis was completed in order to explore the potential effect of exercise interventions on depressive symptoms for adolescents (aged 13 to 17 years).