Étude de l'influence de l'asymétrie de vitesse du tapis roulant à deux courroies sur la biomécanique de la locomotion chez le sujet sain

Abstract

Problematic: In the past, few studies have analyzed the spatiotemporal and electromyographical (EMG) modifications when healthy subjects walked in an asymmetric environment controlled by a split-belt treadmill. These, in order to show each leg has its own gait pattern. Some of these studies proposed a sequence of walking trial alternating asymmetric and symmetric trials always in the same order. Other studies proposed several combinations of asymmetric trials with different asymmetric ratios, and always in the same sequence order. Usually asymmetric ratios were high and the incremental ratio was not kept constant. To the author knowledge, no study by far has proposed randomly asymmetric trials combinations in order to eliminate the sequence effect. Moreover only one author (Reisman et al., 2005, 2007, 2009), measured the stride and step lengths but with a modified versions. The latter do not match with the ground walking definitions as proposed in the literature. Finally, no study has attempted yet to analyze the ground reaction forces in asymmetric environment. Aim: The goal of this Thesis is to study spatiotemporal, ground reaction forces and EMG activities modifications during asymmetric walking in split-belt treadmill. Different asymmetric ratios were assessed in a randomized condition where the increment increases steadily by 10%. This small increment was set to verify if the behavior of the spatiotemporal and EMG activities variables match with what it was found previously with high asymmetric ratios. The predictability of the spatiotemporal parameters was assessed in this study. Methodology: Twenty (17) healthy adult subjects took part in the experimentation. Each subject carried out a total of eighteen walking trials on a split-belt treadmill at different asymmetric ratio. Each trial lasts for 5 min. First, the speed of the belt located under the dominant leg was randomly set at three reference speeds: Vref1=0,75m/s, Vref2=1m/s, as well as Vconf. The latter corresponds to the subject’s comfortable walking speed. Then, the speed of the belt located under the non dominant contra-lateral leg was randomly set to 0%, 10%,20%, 30%, 40%, and 50% less than the dominant ipsilateral side speed. For each reference speed, the experiment was repeated twice. Kinematics data was collected by a 3D an optoelectronic motion analysis system (VICON M460) using six (6) cameras at 120 Hz. Two KISTLER force plates recorded the ground reaction forces at 120Hz. EMG data of Gastrocnemius, Tibialis anterior, Rectus femoris and Semi tendinous of both side were collected at 2000Hz using eight (8) electrodes (DELSYS, Myomonitr III) system. The following spatiotemporal variables were assessed: stride cycle time, stance time, double support time, swing time, stride length, step length, step width. The parameters extracted from the ground reaction forces are: peak amplitudes and timing of medial peak force, lateral peak force, anterior peak force, posterior peak force, 1st and 2nd vertical peak forces. For the EMG activity and for each muscle three parameters were defined: the onset, the offset as well as the activation duration. For each trial, the ten (10) most repeatable gait cycles were kept for the analysis based on the index of repeatability. A one-way analysis of variance (ANOVA) was carried out to test for significant effect of the asymmetric ratio on the spatiotemporal, EMG as well as the ground reactions forces parameters separately. Results: During the asymmetric ratio conditions, we observed a reorganization of gait pattern. Spatiotemporal and EMG parameters were in agreement with previous studies except for the double support time, where we notice a difference between ipsilateral and contralateral double support phase. Our study reveals that the stance time parameter is highly predictive, whereas stride cycle time and step width had a very low degree of prediction. Moreover we defined a new method to estimate the stride and step length which were found to be close to the ground walking. Ground reaction forces exhibit a significant difference between each leg, except for the 2nd vertical peak where the variations with respect to the asymmetric ratio were similar for both legs. The Gastrocnemius activation of the dominant side occurred earlier during the gait cycle and last longer. For the non dominant side one, the activation appeared later and last shorter. The Rectus femoris activation of the dominant side reduced during swing phase up to cancel it when the asymmetric ratio was high. Conclusion: Gait pattern of each leg is altered differently when different asymmetric conditions of walk are imposed. The results can help to develop rehabilitation exercises for getting a better symmetrical gait pattern for people who has asymmetric gait pathology such as hemiparesis.

Date	19 May 2010
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Rachid Aissaoui (Supervisor) & Sylvie (UdeM) Nadeau (Co-supervisor)