Background: Following a stroke, strength gain of the trained affected lower-limb muscles has been observed to result in a change in gait speed, but its effect on other variables related to gait performance has scarcely been studied. The aim of this study was to assess the effect of strength gain of the affected plantarflexors and hip flexors on bilateral levels of effort during gait, in the sagittal plane of movement.
Methods: The levels of effort of 24 chronic hemiparetic participants (mean (standard deviation (SD)): 57.3 (SD 15.5) years), who had strength gains in the ankle and hip muscles following a strengthening programme, were estimated with the muscular utilization ratio during self-selected and maximal speeds. The ratio relates the net moment in gait relative to the muscle's maximal capability. The peak value and the area under the curve of the ratio were used as main outcome measures.
Findings: Regardless of speed, strength gains have been noted to cause a significant 12-17% decrease in the peak value of the ratio of the affected plantarflexors and hip flexors with a reduction of the area under the curve of the affected hip flexors' ratio and a trend toward a decrease for the affected plantarflexors at maximal speed. A significant, albeit small increase in self-selected and maximal gait speeds (P<0.05) was also observed post-training. Regardless of assessment time, the peak value of the affected plantarflexors' ratio was greater than that of the affected hip flexors at self-selected speed (P=0.006) and the area under the curve of the affected hip flexors' ratio was greater than that of the affected plantarflexors (P=0.007) at maximal speed. Generally, negative associations (-0.32<r>-0.83) were noted between the changes in the peak value of the ratio and strength but not between the changes in gait speed.
Interpretation: The decrease in the peak value of the ratio could be explained by the increase in strength. Becoming stronger, hemiparetic participants favoured a reduction of their levels of effort during walking instead of substantially increasing their gait speed.