Effect of Prolonged Running-induced Fatigue on Free-torque Components

Abstract

Running is a popular sport because it demands physical activity and can be performed at a convenient time in any place (Ida et al., 2010). Although running has a positive effect on health, it can have a negative impact on the body because of possible injury. In particular, the incidence of injury from prolonged running is reported to be 30~ 79% (Lun et al., 2004; Taunton et al., 2003; van Gent et al., 2007). There are various possible factors involved in injury from prolonged running, including mechanical abnor- malities previous injuries sex, body mass index, training frequency, intensity, and duration, muscle strength, flexibility, shoes, and fatigue (Taunton et al., 2003). Among prolonged running injuries, stress fractures are a common problem and account for a large proportion of running injuries (Taunton et al., 2002). In prolonged running, stress fractures of the tibia are most common, accounting for 35~56% of the stress fractures caused by prolonged running (Romani et al., 2002). One of the bio- mechanical factors causing tibial stress fractures is free torque (FT) (Milner & Davis, 2006). FT refers to the torque in the vertical axis that is generated by friction between the foot and the ground during the support phase in