, very small to small but non-significant intervention effects for all outcomes variables were apparent. Subgroup analyses showed that training volume, age and study design typically have a small 3 influence on the overall intervention with high training volumes, younger children/adolescents and RCTs yielding the largest effects. However, results for each subgroup were still in favour of the control group. As a result of the small number of studies examining the other psychological outcomes, no other subgroup comparisons could be made.