Plantarflexor weakness as a limiting factor of gait speed in stroke subjects and the compensating role of hip flexors

Objective: To determine, using the Muscular Utilization Ratio (MUR) method, whether plantarflexor weakness is among the factors preventing stroke subjects from walking at faster speeds. Potential compensations by the hip flexors were also examined. Design: A convenience sample of 17 chronic stroke subjects in a context of a descriptive study. Background: Gait speed is correlated with the residual strength of the muscles involved in gait in stroke subjects. However, it has not been established if this residual strength limits gait speed. Methods: Kinetic and kinematic data for comfortable and maximal gait speeds were collected on the paretic side, and were used to determine the moments in plantarflexion (mechanical demand; MUR numerator) during the push-off phase. The maximal potential moment (MUR denominator) of the plantarflexors during gait was predicted using an equation derived from dynamometric data collected with a Biodex system. The MURs of the plantarflexors were then calculated at every 1% interval of the push-off phase. The pull-off phase of gait and the hip flexor strength were also examined. Results: Ten subjects of the sample had a MUR value between 80 and 150% at maximal gait speed. These subjects produced the lowest peak torques in plantarflexion. Each of the four fastest subjects of this group had a large hip flexion moment during the pull-off phase of gait and produced high hip flexion torque values on the dynamometer. Each of the seven remaining subjects had a MUR value under 70% when they walked at maximal speed. Conclusions: Weakness of the plantarflexors should be considered as one factor limiting gait speed in 10 hemiparetic subjects. Some subjects with weak plantarflexors could walk rapidly because they compensated with the hip flexors. For the remaining stroke subjects, factors other than weakness of the plantarflexors have to be considered in order to explain the reduction in their gait speed.