Asymétries locomotrices réelles et perçues lors de différentes conditions de marche sur tapis roulant chez les personnes saines et hémiparétiques

Locomotor asymmetry is frequently observed in individuals following a stroke despite their capacity to perform more symmetrically on demand or after some interventions. Therefore, the underlying causes of such asymmetry and its persistence despite interventions are sources of many questions. This project aims to improve knowledge about the factors that could explain locomotor asymmetry following a stroke. The main objectives were 1) to quantify net joint moments and muscular levels of effort in the lower limbs during different walking conditions on a split-belt treadmill with the aim of determining if these factors could be among those explaining locomotor asymmetry; and 2) to quantify the capacity to perceive locomotor asymmetry in healthy individuals and those post-stroke. The general hypothesis was that locomotor asymmetry is a strategy used by individuals post-stroke to perform with symmetrical levels of muscular effort or to avoid overly high levels of muscular effort, as assessed by the muscular utilization ratio (MUR). The results were presented in four articles (#2 to #5). The first study quantified the effect of split-belt treadmill walking in net joint moments of the lower limbs in healthy individuals and those post-stroke. Overall, the results showed that placing the paretic limb on the slow belt increased the plantarflexion moment in post-adaptation and that such increase was correlated with the increase in contralateral step length. The second study showed that individuals with high levels of effort in the paretic plantarflexors (PF) were asymmetrical in their efforts between sides for PF and hip extensors, whereas the group with low levels of effort in the paretic PF had symmetrical levels of effort in all muscle groups. In addition, both groups showed asymmetrical plantarflexion moments, but only in the group with high levels of effort was this asymmetry related to the asymmetry of residual forces. This suggests that muscle weakness plays an important role in reducing the paretic PF moment for individuals with high levels of effort in PF while other factors must be considered to explain the joint moment asymmetry in individuals with low levels of effort in PF. The third study showed that a more symmetrical gait pattern (temporal or spatial) following walking on the split-belt treadmill required high levels of effort (over 85%) in paretic PF. The fourth study evaluated the ability to perceive locomotor asymmetry in healthy individuals with a protocol on a split-belt treadmill. The gait pattern was perceived as asymmetrical when the temporal asymmetry ratio reached the threshold of 1.05. The low intra-individual variability suggested healthy individuals had a good ability to detect asymmetry. Supplementary results of this thesis showed that individuals post stroke perceived temporal asymmetry better than spatial asymmetry. Overall, these results suggest that muscle strength and muscular level of effort in paretic PF need to be considered as potential factors explaining locomotor asymmetry in individuals post stroke. Further studies are needed to determine the perceptual abilities of locomotor asymmetry in individuals post-stroke.

Keyphrases: Locomotor asymmetry, Muscular effort, Stroke, Biomechanics, Rehabilitation