Elusive ‘usual’ warm-up in injury prevention trials: the problem of comparing apples to beans

Comparing apples to oranges is rational when comparing different fruits; comparing apples to beans is something else entirely. Likewise, injury prevention trials proposing warm-up interventions should strive to deliver reasonable comparisons. The contents and dosage of the intervention and control warm-ups may vary, especially in the context of pragmatic trials, but should be appropriately described to afford transparency and comparability. So, what is this elusive entity known as the ‘usual’ warm-up in injury prevention trials? And how may this affect the interpretation of the findings? This editorial explores the context and importance of the ‘usual’ warm-up in injury prevention trials and provides recommendations to harmonise future research. Warm-up protocols focused on injury prevention are often compared with other warm-ups to assess their relative effectiveness. Pragmatic trials often compare a standardised protocol (the intervention) to ‘usual’ warm-up (the comparator), and this is relevant to reflect current real-world practices. However, accurate evaluation of effectiveness requires clear descriptions of the content of the comparator warm-up protocols. Inadequate and incomplete reporting is more common than desirable, even in recent randomised studies published in high-profile journals.1–3 We describe three examples in detail to illustrate this problem. Example 1 : A cluster randomised trial compared the effectiveness of the warm-up programme ‘VolleyVeilig’ in reducing injuries (35 teams, n=282 players) to ‘usual’ warm-up (31 teams, n=236 players).1 While the ‘VolleyVeilig’ programme was described in detail, there was no information regarding the ‘usual’ …