Prevention of hamstring injuries in male soccer: Exercise programs and return to play

The aim of the studies reported in this thesis was to investigate strategies for the prevention of hamstring injuries. Hamstring injuries are the most prevalent muscle injury in soccer. In spite of efforts to reduce the occurrence of hamstring injuries in soccer, injury rates have not decreased over the last three decades. Therefore, research on hamstring injury prevention is necessary to reduce hamstring injury rates.

Exercise programs to reduce soccer injuries are easy to implement during regular training sessions, are cost effective, and can even improve performance. Our systematic review concluded that there is inconclusive evidence about the effectiveness of general exercise-based training programs for the prevention of soccer injuries. Compliance with the exercise program and tailoring the exercise program to the intended users were found to be important factors influencing the effectiveness of exercise programs.

Therefore, we conducted research on an exercise-based injury prevention program that specifically aims to reduce the risk of hamstring injury, namely, the Nordic Hamstring Exercise (NHE). In a randomized controlled trial involving 579 high-level amateur soccer players, we found that a tailored 12-week NHE-protocol implemented during regular soccer training resulted in a three- to fourfold reduction in the risk of hamstring injury, but it did not influence the severity of the hamstring injuries.

In the same population, Sit-and-Reach Tests (SRT) were performed to assess hamstring flexibility. It is generally assumed - and confirmed via population-based reference values provided by our study - that soccer players have reduced hamstring flexibility compared to other (sports) populations. It is also commonly hypothesized that this could increase hamstring injury risk. However, our longitudinal cohort study found no relationship between hamstring flexibility and hamstring injury risk. Possible confounders, such as age and previous hamstring injury, did not appear to influence this relationship.

If preventive measures fail and the athlete rehabilitates, ultimately, every athlete will ask the same thing: “Can I play again”? This question about return-to-play (RTP) after hamstring injury is a subject of growing interest in conferences, the media, clinical practice, and the scientific literature, although the concept of RTP remains unclear.

We systematically reviewed the literature on definitions of, and criteria for, RTP after hamstring injury used in clinical research. Only few studies provided a definition of, or criteria for, RTP after hamstring injuries. No criteria had yet been validated in prospective studies.

Based on this literature review, a Delphi consensus procedure was carried out to clarify the definition of, and criteria for, RTP after hamstring injury. A worldwide panel of experts selected by the FIFA Medical Centers of Excellence achieved consensus that RTP after hamstring injury should be defined as ‘the moment the player has received criteria-based clearance and is mentally ready for full availability for match selection and/or full training.’ The expert panel also reached consensus that the absence of pain on palpation, during strength and flexibility testing, and during performance testing, similar hamstring flexibility, psychological readiness, performance on field testing, and medical staff clearance were important criteria to assess RTP readiness after hamstring injury.