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

Kristian Thorborg, M Sportsphysio, PhD


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

In This Article

Overview of Original Article


To identify the intrinsic and extrinsic risk factors associated with sport-related hamstring muscle injuries.

Data Sources

MEDLINE, the Cochrane Library of Systematic Reviews up to August 2011, and 6 other databases were searched using words related to the study objective. Google Scholar was used to track citations, and reference lists of included studies were scanned to find additional relevant studies.

Study Selection

The selected prospective, full-text studies in humans, published in the English language, could include either first-time or recurrent hamstring muscle injuries that were sport-related. Discrete data for the hamstring injury outcome had to assess intrinsic or extrinsic risk factors. Tendon and avulsion injuries and nonspecific musculoskeletal injuries were excluded, as were intervention, retrospective, and cross-sectional studies and nonsystematic reviews. Of 1649 articles identified by the searches, 26 were included, plus a further 8 studies identified through citation tracking. Thus, 31 prospective studies and 3 reviews were selected.

Data Extraction

Details of the participants, the injuries and diagnosis, the sport involved, the risk factors investigated, and the outcomes and follow-up were extracted by the authors, who both assessed the studies' methods. For continuous data, standardised mean differences (SMD) and 95% confidence intervals (CI), were calculated. Metaanalysis was conducted where possible using a random effects model.

Main Results

Hamstring injuries were investigated in 14 studies of Australian football, 10 studies of soccer, 5 studies of track and field, and 2 studies of rugby. The follow-up period varied between 3 weeks and 8 years. The study method scores ranged from 44% to 94%, with 12 studies not adjusting appropriately for confounding factors such as previous injury and age. Older age was associated with probability of injury in a metaanalysis of 7 studies (SMD, 2.5; 95% CI, 0.78–4.15) and in a separate analysis of 3 studies (odds ratio [OR], 2.46, 95% CI, 0.98–6.14). Meta-analyses of 8 studies, including 2952 athletes, found previous hamstring injury to be a risk factor for future injury (relative risk [RR], 2.68; 95% CI, 1.99–3.61 and OR, 4.06; 95% CI, 2.39–6.89). Body mass index, weight, and height were generally not associated with first or recurrent hamstring injuries. There was little evidence from 11 studies that the ratio of hamstring to quadriceps strength was a risk factor for hamstring injuries, whatever the speed and contraction type of the testing. In 4 studies, hamstring peak torque was not found to be a risk for hamstring injuries (SMD, 20.24; 95% CI, 20.85 to 0.37). However, in 4 studies, increased quadriceps peak torque did appear to be a risk factor for hamstring injuries (SMD, 0.43; 95% CI, 0.05–0.81). Factors such as strength asymmetries, limb dominance, playing position, flexibility and fitness were not consistently associated with hamstring injuries.


Among many risk factors that were investigated only older age, previous hamstring injury, and increased quadriceps peak torque were associated with an increased risk of sustaining a future sport-related hamstring strain injury.