Directional patterns of muscle activation at the lower limb in subjects with hemiparesis and in healthy subjects: A comparative study.

This article reports the results of a comparative study on directional patterns of muscle activation at the lower limb in 15 subjects with hemiparesis and 18 healthy subjects. Subjects were required to exert static hip and knee torques using multidirectional and biarticular dynamometers designed for the lower limbs. Hip torques were performed in abduction, adduction, flexion, extension, and in combined directions (e.g., hip flexion and abduction) and knee torques were exerted in flexion and extension. The required torque levels corresponded to approximately 5% of the maximal voluntary contraction of healthy subjects. Electromyographic (EMG) activities of the rectus femoris, biceps femoris, gracilis, gluteus medius, gluteus maximus, vastus lateralis, tibialis anterior, and soleus were recorded during these torques. The descriptive analysis involved comparison between either the polar plots (for hip tasks) or the histograms (for knee tasks) representing the mean muscle activity obtained across subjects during torques exerted in each direction for the three groups of muscles analyzed (normal, paretic, and nonparetic muscles). Ciucular statistics were also used to characterize directional patterns of activation in each muscle during hip tasks while linear statistics permitted one to analyze these patterns during knee tasks. In general, the results of both the descriptive and inferential statistical analyses indicated that directional patterns of muscle activation during hip and knee torques are not altered in subjects with hemiparesis. These results are in contrast to the disturbances observed previously in a study of directional patterns of muscle activation at the upper extremity in this population. It is suggested that the contrast between the present results and those obtained at the upper limb in subjects with hemiparesis may reflect the difference in the motor recovery of upper and lower paretic limbs or in the severity of spasticity in the muscles involved at the studied joints. Results of this study also showed that the paretic muscles often demonstrate larger EMG signals than normal and nonparetic muscles, especially during knee flexion torques. These last observations, in addition to the fact that some subjects with hemiparesis could not complete all of the tasks with their paretic limb, under-score the muscle weakness inherent to this population.