Heel acceleration at heel strike and slip outcome.
ISPGR 2007, Proceedings of the 18th International Society for Posture & Gait Research, July 14-18, 2007, Burlington, Vermont. Victoria, BC Canada: International Society for Posture & Gait Research, 2007 Jul; :147
The dynamics of the leading leg, especially heel displacement and velocity, have been the focus of several studies yet few researchers have considered heel acceleration. One study has described heel acceleration during slipping, while another study described heel acceleration during swing phase prior to slip initiation. Anterior/posterior heel acceleration may be of interest because it represents the combined effects of leading leg kinetics, which may hold the leading leg reducing the severity of the slip. Heel strike time represents an initial condition to the slip and therefore may be used to identify risk of falling in subjects. Methods: Sixteen young (aged 20-33) and eleven older (aged 55- 67) subjectswere consented to participate in the study and donned a safety harness during all trials. A total of 79 markers were placed on the subjects and tracked during the trials to characterize their motion.Subjects walked across a tiled floor surface instrumented with forceplates.Subjects experienced four walking trials: the floor was dry during the first three trials and then a slippery liquid was applied to the floor without their knowledge for the fourth trial. Anterior/posterior heel acceleration of the leading leg was determined at heel strike. Ankle, knee and hip torques of the leading leg were calculated using a bottom up inverse dynamics approach from ground reaction forces measured at the floor. Joint torques were parameterized at heel strike. Slip trials were classified as falls if the hip centers fell 5%below the local minimum of the dry trial. Results: Recovery subjects were found to have higher posterior heel acceleration at heel strike than fall subjects (p<0.05). Posterior heel acceleration at heel strike was found to correlate with ankle dorsiflexion torque (r=0.61, p<0.001), knee flexion torque (r=0.84, p<0.001) and hip extension torque (r=0.68, p<0.001). Therefore subjects who recovered have larger posterior heel accelerations, which seem to be the result of leading leg torques. Conclusions:The larger posterior heel accelerations at heel strike seem to be a result of leading leg kinetics, particularly the knee torque. Having larger joint torques to pull back the heel at heel strike and early in stancemay be beneficial towards slip recovery. Therefore increasing posterior heel acceleration by increasing activity in knee flexors may be beneficial to reducing falls.
Humans; Men; Women; Age-groups; Age-factors; Accidents; Physiology; Physiological-function; Physiological-factors; Physiological-effects; Physical-reactions; Injuries; Muscles; Muscle-function; Musculoskeletal-system; Models; Knee-injuries; Knee-disorders; Leg-injuries
ISPGR 2007, Proceedings of the 18th International Society for Posture & Gait Research, July 14-18, 2007, Burlington, Vermont
University of Pittsburgh