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Abstract
Background Hamstring injuries are the most common muscle injuries in male amateur soccer. Eccentric strength of the hamstrings is recognized as an important modifiable risk factor, leading to the development of preventive exercises such as the Nordic Hamstring Exercise.
Objective This study aims to investigate the preventive effect of the Nordic Hamstring Exercise on the incidence and severity of hamstring injuries in male amateur soccer players.
Design Cluster-randomized controlled trial with soccer teams as the unit of cluster.
Setting Dutch first class amateur field soccer.
Participants Male amateur soccer players (mean age 24.5 years, SD 3.8 years) from 40 teams were allocated to intervention (n=309 players) or control group (n=310 players).
Risk factor assessment The intervention group was instructed to perform 25 sessions of the Nordic Hamstring Exercise within a period of 13 weeks during the first months of 2013. Both the intervention group and control group performed regular soccer training and were followed for hamstring injury incidence and severity during the calendar year 2013. At baseline, personal characteristics (e.g. age, injury history, field position) were gathered from all participants via questionnaire.
Main outcome measurements Primary outcomes are initial and recurrent hamstring injury incidence (number of hamstring injuries) and injury severity (number of days injured).
Results Interim analysis after intervention (2 months follow-up) show a total of 2 hamstring injuries in intervention group vs 12 hamstring injuries in control group (χ2=7.5, P<.05). Regarding injury severity, no difference was found between intervention and control group (t=0.3, P=.77).
Conclusions Preliminary analyses during the summer break show substantial hamstring injury incidence reduction by incorporating the Nordic Hamstring Exercise in regular training. With a total follow-up of 9 months, final analyses (survival analyses including the number of injuries per 1000 playing hours) will be performed in January 2014.