ELECTRICAL AND MECHANICAL OUTPUT OF THE KNEE MUSCLES DURING ISOMETRICAND ISOKINETIC ACTIVITY IN STROKE AND HEALTHY-ADULTS

Surface electromyography (EMG) and torque were measured from knee flex ors and extensors in 12 control subjects (CS) aged 25-59 years (10 fem ale) and bilaterally in 12 stroke subjects (SS) aged 27-75 years (four female) with hemiparesis and mild clinical spasticity. They performed isometric and isokinetic maximal voluntary contractions (MVC) and als o isokinetic passive movements at angular velocities from 30 to 300 de grees/s. The time taken to walk 10 m was documented. Greater torque wa s recorded during passive extension in the paretic legs when compared with both non-paretic and control limbs (p < 0.01). No EMG activity wa s measured in any subject. Isometric MVC torque of both muscles in the paretic leg was less (p < 0.01) than both the non-paretic and control limbs. The SS generated relatively less torque bilaterally at the low er velocities than CS. Not all SS reached the higher velocities and no ne of the paretic limbs achieved 300 degrees/s during flexion. Gait sp eed correlated with maximal paretic knee extension velocity (p < 0.001 ). The extent of co-contraction during MVCs was generally low or absen t and similar in all three groups. These results suggest a mechanical rather than reflex cause for the restraint detected clinically. Low fo rce generation by the paretic agonists appeared to be the major cause of reduced torque, rather than antagonist opposition.