Anatomical alignment and muscle strength as predictors of overuse injuries in long-distance athletes

Abstract

Background - Running is a popular choice of physical activity for many people because it is relatively inexpensive and not bound to a high-tech facility (Mann et al. , 1981 : 190). Associated with the increased popularity of running is an increase in the incidence of running-related injuries (Mann et a1. , 1981: 190; Wen et al. , 1997: 1291 ). This ranges from as little as 11 percent (Montgomery et al. , 1989:239) to as high as 75 percent (Van Mechelen, 1995:161) depending on which study is cited. In a study by Marti et al. (1988:289), one in five runners were forced to fully interrupt training due to injuries. One in seven sought medical attention, and one in forty were forced to miss work. A clear set of predictor variables that can be used to identify the high risk runner and initiate preventative measures, would therefore be of great value to medical practitioners (Frederickson, 1996:50; O'Toole, 1992:S360). A variety of factors have been identified as role players in the aetiology of running injuries (Krivickas, 1997: 133; Layman & Morris, 1991:33; Montgomery et al., 1989:237; Pinshaw et al. , 1984:291 ; Wen et al. , 1997:1292). These factors can be described as being either intrinsic or extrinsic in nature (Gellman & Burns, 1996:263 . Intrinsic factors refer to inherent characteristics of the runner e.g. anatomical alignment and joint range of motion (Krivickas, 1997: 135) as well as muscle strength characteristics (O'Toole, 1992:S360) and psychological factors (Layman & Morris, 1991:28; Robbins & Joseph, 1985:23). Training errors, faulty equipment and training surfaces on the other hand are external to the athlete and classified as extrinsic risk factors (Krivickas, 1997: 133). The relationship of anatomical alignment measures and overuse injuries in runners is not yet well established, and the results of existing studies are often contradictory

(Krivickas, 1997: 133). Inadequate strength and muscular imbalances are also cited to be important risk factors in the aetiology of running-related injuries (Jonhagen et al. , 1994:226; Kibler et al. , 1991:68; O'Toole, 1992: S360). OBJECTIVES The purpose of this study was to retrospectively examme the importance of anatomical alignment measures in predicting the risk of overuse injuries in runners. The relationship between muscle-strength characteristics and runmng mJunes was also investigated. METHODS Fifty-two runners were recruited from marathon clubs in the Potchefstroom K1erksdorp area. The respondents were subjected to a battery of tests that included a questionnaire, a standard pre-season medical examination, and measuring of anatomical alignment, anthropometric parameters and muscle-strength. Subjects were required to complete a questionnaire pertaining to their training parameters and demographic information. Running-related injuries were diagnosed and recorded during the standard pre-season physical examination. The anatomical alignment measures included forefoot varus, longitudinal arch angle, arch index, leg length discrepancy, knee varus/ valgus, Q-angle, dynamic hip abductor strength (Trendelenberg test), posterior thigh and lower-back flexibility (sit-and-reach), and hip extension range of motion. Muscle strength was measured for both the knee and ankle joint, concentrically as well as eccentrically. From these results it was possible to calculate the conventional and functional strength ratios for knee flexion and extension, and for ankle plantar and dorsiflexion. These values were then compared between injured and uninjured subjects.

RESULTS Accurate sets of predictor variables were identified for male and female subjects respectively. The variables that could predict injured male runners with 94 % accuracy were: forefoot varus, arch index, posterior thigh and lower back flexibility and the percentage body fat. Predictor variables for female subjects included forefoot varus, arch index, longitudinal arch angle, knee varus/ valgus, Q-angle, functional leg length discrepancy, hip extension range of motion and running experience. These variables were 88 % accurate in predicting injured female subjects. Muscle-strength characteristics were not found to be related to the incidence of running injuries in the present study. CONCLUSIONS It is concluded that anatomical alignment measures did play a significant role in the aetiology of running injuries and could be used accurately to injured and uninjured subjects. Interestingly, the only variables that were included in both the male and female models were forefoot varus and arch index. No differences were found in the muscle-strength characteristics of injured and uninjured subjects and subsequently no relationship could be discerned between the above mentioned variables. It appears that muscle strength may not be as important as anatomical alignment in the development of injuries in runners.