In contrast to our hypothesis, we found no preventive effect of The11 on injury incidence or injury severity among male adult amateur soccer players during one season.
Whereas we found no preventive effect of The11 in our study population, consisting of adult men playing at a high amateur level, Junge et al17
found preventive effects of the programme among male youth soccer players. It is conceivable that an exercise programme have greater physical effects in younger players, since they have not yet established their basic movement patterns.27
This may explain why an effect was found in junior soccer players, but not in senior soccer players playing at the highest amateur levels.
A gender effect has been suggested, as The11 includes five exercises with a major focus on balance and knee alignment.28
These exercises aim to improve core stability and neuromuscular control,15
and it is well known that female players have a 2–3 times higher ACL injury risk than male players, related to impaired knee alignment and lack of muscular balance.30
Hence, a preventive effect may be more likely in female soccer players than in male soccer players.13
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
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
For example, exercise 3 of The11 is the so-called ‘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
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.
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 form by the coaches. In case of any inconsistencies between the two recordings about the absence of a player due to injury, a member of the research staff contacted the coach and/or paramedic to verify the absence. Given these procedures, reporting bias and underreporting should have been minimal. If any under-reporting exists, it will be restricted to minor injuries because more than 70% of the injuries reported resulted in absence of more than 1 week.
In conclusion, there are serious doubts that a general, multicomponent training programme such as The11 is effective in this particular population of adult male amateur soccer players. The nonspecific content of the programme, an ineffective intensity, and possibly also the limited number of two training sessions per week available to perform the programme may have caused the programme to become ineffective. Unfortunately, the programme was tested as a single intervention, making it impossible to determine which exercises failed to have an impact on the injury risk. New research should focus on the correct type and dose–response relationship of exercises, specifically addressing risk factors for injuries in adult male amateur soccer players. Such research should at least cover the most frequently reported injuries being ankle, knee, upper leg and groin injuries.
What are the new findings?
Although in some studies The11 was used to reduce injury rates in various populations, its effectiveness has not yet been studied in the largest group of active participants in soccer worldwide: male adult soccer players. In our study among adult male amateur soccer players, The11 did not significantly reduce injury incidence or injury severity.