Reducing gait asymmetry after stroke with strength training

Abstract

Hemiparesis is a common sequel to stroke that typically results in an asymmetrical gait pattern. An experiment was designed to test the hypothesis that plantarflexor (PF) and dorsiflexor (DF) strength training reduces gait asymmetry, and improves neuromuscular activation. Fourteen chronic stroke patients with a comfortable walking velocity (mean = 0.65 m/s (SD 0.48), range between 0.11 and 1.41 m/s) conducted strength training using Thera-bands, 3 days a week over six weeks. Maximum voluntary isometric contraction was assessed using a custom-built apparatus. The twitch interpolation technique was used to determine increases in PF and DF voluntary activation. Timing of muscle activity was also assessed using surface electromyography (EMG) during walking, while a Vicon motion capture system recorded patients’ kinematic data, and kinetic data were recorded from a force-plate embedded in the walkway. Co-contraction of PF and DF was assessed during single muscle voluntary contraction. Patterns of muscle activation were also assessed during walking. Two pre-intervention measures were taken 2-4 weeks apart, one set of post-intervention measures was taken immediately after the training period, and the retention of effects was assessed 6 weeks later. Strength training improved paretic limb PF strength by 45% immediately following strength training, and gains were retained over the following 6 weeks. Reduced effects of stimulation using the twitch interpolation technique supported this finding. Strength also increased by 54% for the non-paretic PF that did not receive training, however this gain was not evident until 6 weeks after the training had been completed. Unwanted co-contraction of gastrocnemius medialis (GM) during tibialis anterior (TA) maximum voluntary activation reduced by 18%. There was an 8% reduction in paretic limb stance time, and a 6% reduction in paretic limb double support time. No significant reductions in other gait asymmetries, EMG timing, or in propulsive forces were revealed. These results provided minimal support for the hypothesis that unilateral strength training of paretic ankle muscles reduces the asymmetry of gait. However, the strength gains in ankle muscles of both limbs, the reduced paretic limb double support time, and the reduced voluntary co-contraction of the paretic limb GM, suggest that strength training is capable of initiating improvements in the control of ankle muscles during walking. The study therefore provided some promising insights into the potential for a simple home-based protocol to enhance ambulatory function in people with chronic stroke.