The effect of weight bearing symmetry on the postural responses of lower limb muscles in hemi-paretic patients

Asymmetric weight bearing is one of the prominent characteristics of impaired postural control in hemi-paresis after stroke. Considering the important effect of load exerted on limbs in correcting postural reflexes، the effect of sole on weight bearing symmetry and also the effect of increased load on paretic limb on the postural responses of lower limb muscles against an internal perturbation were investigated.

27 hemi-paretic post-stroke patients، who were able to stand independently without assistive devices for one minute، participated in this study. Evaluations included measuring symmetry index، the latency and amplitude of postural responses of lower limb muscles that was carried out before and after placing a 10-mm-thick sole under intact lower limb of patients. To measure symmetry index، the patients were asked to stand on force platform for 20 seconds. Electromyographic recordings from medial gastrocnemius، soleus and lateral hamstring muscles of paretic and non-paretic limbs were obtained for evaluating postural responses. Rapid flexion movement of non-paretic upper limb was used as an internal perturbation for exciting postural muscle responses.

The effect of lift on improving symmetry index was significant (P = 0. 001). Increasing load on paretic limb did not exert any effects on the latency and amplitude of postural responses.

Inserting a lift improved symmetry by shifting center of gravity toward midline. The results of the present study show that decreased load on a paretic limb following stroke cannot fully explain the weak and latent responses of postural muscles.