What factors are involved in hamstrings injury?
Hamstrings injury is the most frequent muscle injury in sports that require high speeds, such as football, rugby or American football.
Muscle injuries are a major concern in the world of football. These injuries occur approximately 4.6 times every 1000 hours of activity, being much more frequent than others produced by blows, fractures or joint injuries (López-Valenciano et al., 2019). Muscle injuries have significant negative consequences for both team performance and the club’s economy, as athletes who suffer them are on average two weeks away from the team (Ekstrand, Hägglund, & Waldén, 2011). Therefore, the focus on preventive strategies for muscular injuries is fundamental.
Professional teams try to implement evidence-based prevention programmes, i.e. by combining the findings of the scientific literature with the knowledge gained from the experience of the professionals themselves. However, it is currently unknown what is the “best evidence” for existing strategies, which depends not only on the results – beneficial or not – found by various scientific studies, but also on the possible risk of bias (i.e. methodological quality) of such studies. For this reason, a group of professionals with great relevance both in the field of research and professional football, which include Maurizio Franchini (physical trainer at AS Roma), Ricard Pruna (head medical doctor at FC Barcelona) or Gregory Dupont (physical trainer at Real Madrid CF), have evaluated all the existing evidence so far regarding muscle injury prevention programs for elite football players over 16 years old (Fanchini et al., 2020).
After an extensive search, the authors found 15 studies that met the established criteria, including both systematic reviews (considered level 1 evidence) and randomised and non-randomised controlled studies (levels 2 and 3 evidence, respectively). The systematic reviews – which pooled evidence from different studies – showed contradictory results, as while some supported eccentric exercises or programs that included balance, stabilization and flexibility exercises, other reviews concluded that there is not enough evidence to support these strategies. The same was true for level 2 studies (the randomised controlled studies), with 3 studies supporting eccentric exercises and 2 not. In contrast, all of the smaller studies supported the benefits of different injury prevention strategies. Not only was there controversy regarding the efficacy of interventions to reduce injuries, but also a large number of the studies included were shown to be at high risk of bias. In fact, the two systematic reviews that were considered to be ‘low risk of bias’ concluded that no single exercise (including some common ones such as eccentrics, balance exercises, and hamstring eccentrics in particular) has sufficient evidence to support its effectiveness, while most studies supporting the benefits of different exercises were at ‘high risk of bias’.
Given these results, Ricard Pruna comments that “given the lack of scientific evidence for all methods, this reaffirms that the best strategy is an individualized protocol for all players. This protocol will vary depending on the player, the time of the season, what type of injuries the player has suffered in the past, etc. This protocol will also vary over time depending on the variables affecting the player”.
As authors comment, sports professionals should rely primarily on systematic reviews and randomized controlled studies to guide their decisions, besides, they should not only take into consideration their findings but also to their methodological quality and possible risk of bias.
Furthermore, only 5 randomised controlled studies were included in the review, reflecting the need for more studies of this type on elite football players. Conducting these studies in top-level athletes is complicated by the large amount of resources (time, money, need to adapt to club dynamics) required for this.
Therefore, as the authors conclude, in the absence of high-level evidence, consensus among experts may be the best option to guide evidence on the most effective strategies, thus bringing together both practical and scientific experience.
Ekstrand, J., Hägglund, M., & Waldén, M. (2011). Epidemiology of muscle injuries in professional football (soccer). American Journal of Sports Medicine, 39(6), 1226–1232. https://doi.org/10.1177/0363546510395879
Fanchini, M., Steendahl, I. B., Impellizzeri, F. M., Pruna, R., Dupont, G., Coutts, A. J., … McCall, A. (2020). Exercise-Based Strategies to Prevent Muscle Injury in Elite Footballers: A Systematic Review and Best Evidence Synthesis. Sports Medicine, (0123456789). https://doi.org/10.1007/s40279-020-01282-z
López-Valenciano, A., Ruiz-Pérez, I., Garcia-Gómez, A., Vera-Garcia, F. J., De Ste Croix, M., Myer, G. D., & Ayala, F. (2019). Epidemiology of injuries in professional football: A systematic review and meta-analysis. British Journal of Sports Medicine, 1–9. https://doi.org/10.1136/bjsports-2018-099577
An article published in The Orthopaedic Journal of Sports Medicine —in which members of the club’s medical services participated— now suggests to consider the detailed structure of the area affected, and treating the extracellular matrix as an essential player in the prognosis of the injury.