Electromyography characterization of stretch responses in hemiparetic stroke patients and their relationship with the Modified Ashworth Scale

Abstract

To determine the validity of the Modified Ashworth Scale as a measure of spasticity by determining its relationship to surface electromyography activity and contracture. A controlled study of hemiparetic stroke patients with spasticity. A physiotherapy department in a secondary care hospital. Thirty-one stroke patients and 20 healthy volunteers. The resistance to passive movement around the knee and ankle of the affected and unaffected legs was rated using the Modified Ashworth Scale. Passive range of movement was measured with a goniometer. Surface electromyography recordings of four lower limb muscles were taken during passive stretches of the knee and ankle. Hemiparetic patients produced surface electromyography responses to stretch that were of greater amplitude (unaffected limbs: mean = 25.82 mV (43.85), affected limbs: mean = 24.77 mV (35.46)) than those of healthy volunteers (mean = 15.85 (29.96)). The affected muscles of hemiparetic patients were more likely to produce surface electromyography responses to stretch of a sustained duration (45% of cases) compared with unaffected limbs (24% of cases) and those of healthy volunteers (16% of cases). The Modified Ashworth Scale showed a positive correlation with the magnitude (p < 0.05) and duration (p < 0.001) of the surface electromyography response. High scores on the Modified Ashworth Scale were associated with contracture (p < 0.001). Contracted muscles produced significantly greater surface electromyography reflex responses compared with noncontracted muscles (p < 0.05). The Modified Ashworth Scale reflects spasticity in terms of surface electromyography stretch responses produced by passive movement, but the relationship of spasticity to contracture remains unclear.