What Are the Most Important Risk Factors for Hamstring Muscle Injury?

Kristian Thorborg, M Sportsphysio, PhD

Disclosures

Clin J Sport Med. 2014;24(2):160-161. 

In This Article

Commentary

Freckleton and Pizzari are to be commended for providing the sport medicine community with the most comprehensive literature search and syntheses to date of studies relating to risk factors for hamstring muscle injury. The topic is of interest to all sport medicine practitioners concerned with the management of this most common muscle injury in sport.

The greatest strength—but also weakness—of the review by Freckleton and Pizzari is in the pooling of data. The strength is that statistical power is potentially increased by including more injuries (events) associated with the individual risk factors being investigated.[1] However, the weakness of pooling data that appear to be unadjusted is that important interaction effects or confounders may be missed, as the authors mentioned as a limitation of their study.

The identification of risk factors was considered a critical step in the 4-step sequence of injury prevention that was introduced by van Mechelen et al.[2] The reason for this is that risk factors related to a specific injury should offer information on the underlying causes for the particular injury.[1,2] Thus, information on risk factors may suggest strategies for future injury prevention.[2] Although this idea is simple and appealing, the multifactorial nature of injuries in sports may sometimes interfere with this approach, especially in prospective risk factor studies in which important factors, known and/or unknown, are not taken into account.[1]

The present systematic review agrees with previous studies in identifying older age and previous hamstring muscle injuries as risk factors for subsequent hamstring muscle injury. The role of quadriceps and hamstring muscle strength seems less clear. Based on the investigators' statistical analyses, increased quadriceps strength is a risk factor for hamstring muscle injury, whereas hamstring weakness is not. Does this mean that injury prevention should focus on systematic quadriceps strength reduction (immobilization would be quite effective for this) in athletes at risk of hamstring muscle injury—instead of eccentric hamstring strengthening? Probably not, especially as eccentric hamstring strengthening has been shown to be an effective injury-preventative strategy.[3] Although the van Mechelen model may be theoretically useful, in reality our understanding of risk factors may suffer from not taking the multifactorial nature of hamstring muscle injuries into account.[1]

Freckleton and Pizzari suggest that previous injury and age should be considered in a multivariate model when other risk factors are investigated. However, based upon their findings of increased peak quadriceps strength as a risk factor for hamstring muscle injury it may also be relevant to include this isolated variable in multivariate analyses, to investigate interaction or confounding effects. Future studies of potential risk factors for hamstring muscle injury should also include adjustment for individual athletic exposure hours,[1] particularly focusing on match-play exposure in high-risk hamstring-injury sports such as football, because match-play is associated with higher rates of hamstring injuries than is similar time spent training.[3] These factors have not been adequately accounted for in the current literature, which limits our present understanding of risk factors for hamstring muscle injury.

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