Effects of Prolonged Running-Induced Fatigue on the Periodicity of Shank-Foot Segment Coupling and Free Torque

Abstract

Fatigue is defined as lassitude and weariness resulting from a bodily or mental endeavor, a state in which the force or sensitivity in cells, muscles, and organs is temporarily weakened after a prolonged activity or stimulus (Choi & Song, 2003). There are various causes of fatigue, and fatigue induced by exercise is a local phenomenon generated in contracted muscles, in which it is difficult to maintain muscular tension while muscular contraction continues (Choi & Song, 2003; Gibson & Edward, 1985). Fatigue caused by muscle movements such as exercise or physical labor is temporary; it is an acute condition that can be mitigated by rest or sleep (Choi & Song, 2003; McFarland, 1971). Fatigue caused by prolonged running is the main factor that disturbs the exercise by reducing the efficiency of the effort to continuously generate force (James, Dufek, & Bates, 1992; Ryu, 2004). Prolonged running that causes fatigue is a very effective sport that enhances bodily health; however, it can also cause injury and pain because of the physiological limitations of the human body (Elliot & Ackland, 1998). Fatigue due to exercise mainly occurs later during the workout and increases the possibility of injury by damaging muscular force, coordination, and attentiveness (Collins & Whittle, 1989; Ryu, 2016). Therefore, observing changes in the mechanical factors related to injury in the fatigued state due to prolonged running is necessary to predict and evaluate the risk of injury (Ryu, 2004). During bodily movements, the coupling of segments and joints is closely related to injury (Boyer, Silvernail, & Hamill, 2014; Hamill & Haddad, 2002; Ryu, 2004). Among the many couplings that occur during exercise, the coupling of foot inversion-eversion and shank internalexternal rotation is known to be an important motion in predicting the mechanism of potential injury (Nigg, Cole, & Nachbauer, 1993; Nigg, Khan, Fisher, & Stefanyshyuh, 1998; Ryu, 2004). Thus, analysis of the relative change in movement of the coupling in the fatigued state induced by prolonged running would provide quantitative data for clarifying the fatigue itself and the possibility of potential injury (Hamill & Haddad, 2002). Furthermore, investigation of the changes in relevant kinematic factors is not only important to determine the cause of potential injury during prolonged running but also necessary for the successful execution of the exercise. The shank is located proximally to the foot segment; therefore, it is easily exposed to a twist load due to the torque transfer caused in the foot segment, making it vulnerable to injuries such as stress fracture (Pohl, Hamill, & Davis, 2009). While running, the free torque to the vertical axis, which is generated by the frictional KJSB Korean Journal of Sport Biomechanics 2016; 26(3): 257-264 http://dx.doi.org/10.5103/KJSB.2016.26.3.257 http://e-kjsb.org eISSN 2093-9752 ORIGINAL