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

Objectives: To determine the validity of the Modified Ashworth Scale as a measure of spasticity by determining its relationship to surface electromyography activity and contracture. Design: A controlled study of hemiparetic stroke patients with spasticity. Setting: A physiotherapy department in a secondary care hospital. Subjects: Thirty-one stroke patients and 20 healthy volunteers. Main measures: 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. Results: 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). Conclusion: 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.