A dynamic EMG profile index to quantify muscular activation disorder in spastic paretic gait

Spasticity is a complex phenomenon that interferes with motor control. Existing clinical and physiological measures of spasticity have mainly focused on the evaluation of clonus and reflexes. Subjected to the limitation of testing in a resting position, the results may not necessarily reflect the extent of functional impairment caused by spasticity. To evaluate spasticity in a dynamic, voluntary movement such as locomotion, a task-specific approach is essential. A dynamic index, I, derived from the EMG activity obtained during treadmill walking in human subjects, is therefore proposed as a functionally relevant measurement of spasticity in locomotion. I, defined as the ratio of integrated EMG in the pre-determined 'off' window of the normalized gait cycle to that in the 'on' window, would indicate the degree of abnormal activation of locomotor muscles from their normally relaxed state as compared to the total recruitment in the active state during walking. The present study done on 5 normal and 8 spastic paraparetic subjects showed that I was homogeneously low in the normal group but abnormally high and variable in the spastic group. A case study has further demonstrated that I is sensitive to the alteration in locomotor spasticity with pharmacological intervention, and the change in I parallels the improvement in the kinematics observed. This preliminary study indicates that the proposed index appears to be a functionally relevant and dynamic measurement of spastic locomotor disorder.