more likely in female soccer players than in male soccer players.13 32 The findings of the present study among a male soccer population supports this. It is thus important that prevention programmes such as The 11 sufficiently address the specific injury risk factors relating to gender, age and playing level. A study by Steffen et al18 , which included female youth soccer players, reported no effects of The11. They suggested that low compliance with the programme explained the lack of effects and this was one of the most important reasons to introduce a modified programme: The11+. The11+ includes a greater diversity of exercises, changing both the type and the intensity during the soccer season. Subsequently, Soligard et al reported a preventive effect of The11+ among female youth soccer players. Among others, they reported a reduction in the incidence of knee injuries, which is to a certain extent in line with our results.27,33 The success of the new programme was partially explained by increased compliance to very acceptable levels (77%). However, it seems unlikely that low compliance was a key factor in the lack of an effect achieved with the original The11 programme in our study, as compliance was almost as good as that reported by Soligard et al. The positive effect found by Soligard et al could also suggest that the intensity of The11 may not have been sufficient to achieve adequate preventive effects in our study population.27 33 For example, exercise 3 of The11 is the socalled ‘Nordic Hamstring’ exercise. It has been shown in male soccer players that a gradual increase in the number of repetitions over 4 weeks - from two sets of 5 to three sets of 8-12 repetitions - increases eccentric hamstring muscle strength and decreases the rate of hamstring strain injuries.10,12,34 This graded protocol comes close to the one implemented in The11+. In contrast, the Nordic Hamstring exercise protocol in The11 contains only a single set of five repetitions, which does not vary through the season. This might suggest that the intensity of at least some of the exercises in The11 were not sufficient to decrease the injury rate in our adult male amateur soccer players. Having found no positive effect of the prevention programme among male adult amateur soccer players, we need to return to step two of the model by van Mechelen.20 This means at least that a better understanding is needed of the aetiological factors and injury mechanisms as risk factors for soccer injuries in male adult soccer players. Figure 2 Survival curves based on Cox regression for first soccer injuries during the 2009–2010 season. This study was the first randomised controlled trial documenting the effects of The11 on male adult soccer players. Ideally, randomisation in trials should take place at the level of the subjects (players). Given the settings and methods in this trial, both practical and theoretical reasons made it impossible for such a randomisation to be applied. Alternatively, randomisation at the level of teams would have been the preferred route. However, it would not have been acceptable if some teams could possibly profit from the programme, while others in the same competition could not. As a result, randomisation had to take place at district level, which led to a higher number of players being included in the trial. In view of the expected large number of injuries in this study, verification of the injury diagnosis by an independent medical doctor was impossible to implement. However, the recording of injuries as well as the diagnosis was assumed to be very reliable. Using the definitions in the consensus statement on injury definitions and data collection in soccer,23 injuries were recorded primarily by local, well-trained paramedics. Any injury that may have been missed was likely to be recorded in the weekly exposure nummer 5 | december 2012 | Sport & Geneeskunde 11 Pagina 10
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