DIFFERENCES IN MUSCULAR CONTROL AND GROUND REACTION FORCES IN SUBJECTS WITH STABLE AND UNSTABLE ANKLES

Abstract

The aim of this study was to investigate if there is a common behaviour distinguishing subjects with stable ankles from those with unstable ankles. Therefore the muscular response and the ground reaction forces (GRF) of 24 subjects performing horizontal jumps and also drop landings from a 40cm high box, on three different surfaces (a level one and two surfaces inclined 3° either laterally or medially) were measured. Eight parameters of the EMG signals from each of six muscles of the lower leg and several GRF parameters (eight for jumping and seven for landing) were analysed. EMG data reveal that stable subjects have higher mean power frequencies (MPF), whereas unstable subjects increase their amplitudes. The GRFs show significant differences (p<0.05) for the 2nd vertical force maximum (Fz2) and its slope (Fz2slope), for the contact time (CT) and for the force maximum in medial direction (FYmin) The one-legged horizontal jumping task, as well as the inclined ground conditions, seem to provide a better discrimination regarding ankle stability than the drop landing task and the level ground condition.