Purpose: The "11+ Kids" injury-prevention program has been shown to reduce injuries and related costs in youth football players less than 14 y of age. A major argument to convince coaches to use this exercise-based injury-prevention program is a potential performance enhancement of the players. Therefore, this study investigated the effects of the "11+ Kids" program on isokinetic strength. Methods: Two teams were randomly assigned to the intervention and control groups. The intervention group replaced their warm-up by the "11+ Kids" and the control group warmed up as usual. Two days before and after the 10-wk intervention, isokinetic strength of the hip adductors and abductors, knee flexors and extensors, and ankle invertors and evertors was tested. Results: Thirty-one players (mean age 11.5 [0.8] y) completed the study. The intervention group showed large improvements in all isokinetic strength measures (P<.001 for all measures; Cohen d=0.8-1.4), whereas the control group only showed negligible to medium positive effects (P values ranging from .006 to .718; Cohen d=-0.1 to 0.7). The intervention was beneficial compared with the control group regarding isokinetic strength of the hip adductors (P<.001), knee flexors (P=.002), and ankle evertors (P<.001) and invertors (P=.005). Conclusions: Given the relatively short intervention period of 10 wk, the observed improvements relate to a practically meaningful effect of the intervention. The gain in strength may improve players` performance and may contribute to a reduction of injury risk in the long-term application.
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