Table 1 Study quality score key

Study reference:	Score
How was allocation to the intervention group done?
2 = random
1 = cluster random
0 = historical comparison/volunteer or convenience group
Was the assigned intervention concealed before allocation?
2 = adequate
1 = unclear
0 = inadequate/impossible
Were the outcomes of participants who withdrew described and included in the analysis (intention to treat/effect of compliance)?
2 = withdrawals well described and accounted for in analysis
1 = withdrawals described and analysis not possible
0 = no mention, inadequate mention, or obvious differences and no adjustment
Were the outcome assessors blinded to treatment status?
2 = effective action taken to blind assessors
1 = small or moderate chance of unblinding of assessors
0 = not mentioned or not possible
Were the inclusion and exclusion criteria (age, previous injury, sport) clearly defined?
2 = clearly defined
1 = inadequately defined
0 = not defined
Were the intervention and control group comparable at entry?
2 = good comparability of groups, or confounding adjusted for in analysis
1 = confounding small; mentioned but not adjusted for
0 = large potential for confounding, or not discussed
Were the interventions clearly defined?
2 = clearly defined interventions are applied
1 = clearly defined interventions are applied but the application is not standardised
0 = intervention and/or application are poorly or not defined
Were the outcome measures used clearly defined? (injury: self-reported injury/medically confirmed/severity defined)
2 = clearly defined
1 = adequately defined/recorded
0 = not adequately defined/recorded
Was the surveillance period active and of clinically appropriate duration?
2 = active surveillance and appropriate duration
1 = active surveillance, but inadequate duration
0 = surveillance not active or not defined
Total score (18 = 100%)