A prospective investigation of the association between isometric muscle strength and running related Injury among novice and recreational runners

Introduction Recreational running has many health, social and psychological benefits. However, there is a considerable risk of developing a running related injury (RRI) (1). Therefore, understanding the aetiology of these injuries, with a view to reducing the risk of their development is of paramount importance. Deficits in muscle strength is a proposed risk factor in developing RRIs, though conflicting evidence exists to support this claim (2,3). The majority of this research has been retrospective, limiting the ability to establish a causal relationship. Furthermore, many studies have had small sample sizes, low relative numbers of injured participants or employed isokinetic machines, which have practical limitations. This study aims to prospectively investigate the impact of isometric muscle strength on the likelihood of sustaining a RRI. Methods: One hundred and seventy six injury-free recreational and novice runners (66 females, 110 males, 42.5±9.2 yrs) were recruited. During a single baseline session, three measures of the maximum isometric strength, normalised to body mass, of the following five muscle actions were recorded bilaterally using a hand-held dynamometer (HHD) (J-Tech, USA); hip abduction and extension, knee flexion and extension and ankle plantar flexion. A RRI was defined as any lower limb and back injury persisting for at least 7 days or 3 consecutive training sessions, causing restriction of running or requiring medical consultation (4). RRIs were tracked prospectively via email for a period of six months. Backwards logistic regression analysis was performed to investigate the impact of isometric muscle strength on the likelihood of sustaining a RRI. Multicollinearity was assessed and highly related variables were removed. Results: Fifty-nine participants reported a RRI over the six-month period (INJ: 35 male, 24 female, 43.6±9.5 yrs; UNINJ: 75 male, 42 female 40.3±8.0 yrs). A statistically significant model was able to be generated to predict injury (χ2 =2.57, p=.023), which correctly classified 66.7% of cases with high specificity (95.7%). This was a relatively low improvement on the null hypothesis model, which predicted 66.1% of cases correctly. The model only explained 4.3-5.9% of the variance and the sensitivity was very low (10.2%). Only age (OR=.97, 95% CI:.93-1.0) and hip extension strength (OR=1.5, 95% CI:.89-2.52 ) remained in the model. Conclusions: Isometric muscle strength, as assessed in this study, may not be able to accurately predict a future RRI. Strength measures may not reflect the ability to effectively implement an injury-resistant running technique or may not reflect tissue strength. Given that injuries are caused by high loading relative to tissue strength, future research should examine strength and localised loading during running as combined factors in predicting RRI.