CONTROL OF LEG STIFFNESS AND ITS EFFECT ON MECHANICAL ENERGETIC

INTRODUCTION: In normal daily activity as in sports, humans adjust their physical behavior depending on the ground surface characteristics (Farley et al., 1998; Ferris, Liang & Farley, 1999) by being able to vary their performance (Arampatzis, 1999; Sanders, 1993). A difference in surface stiffness leads to a change in leg stiffness (Farley et al., 1998; Ferris, Liang & Farley, 1999). There are published results on relationships between joint stiffness and oxygen consumption (Dalleau et al., 1998; Heise & Martin, 1993). From this research, it can be concluded that leg stiffness influences athletic performance. The relationship between leg stiffness and performance during explosive movements on a sprung surface has not been reported in the literature to date. Leg Stiffness can be influenced by stride frequency while running (Farley & Gonzalez, 1996) or hopping frequency when bouncing in place (Farley & Morgenroth, 1999). These findings support the idea that it is possible to control leg stiffness by manipulating ground contact times and to consider its effects on mechanical energetic processes during drop jumps on a sprung surface. The purpose of this study is two-fold: a. Examinations of the effect of verbal instructions, given to the subjects for the control of lower -extremity stiffness. b. Assessment of the effect of the leg stiffness on mechanical energetic processes during drop jumps on a sprung surface