EVALUATION OF ANTAGONIST COACTIVATION STRATEGIES ELICITED FROM ELECTRICALLY STIMULATED MUSCLES UNDER LOAD-MOVING CONDITIONS

Muscle coactivation strategies that produce ankle dorsiflexion and pla ntar flexion were elicited bg electrical stimulation of the tibialis a nterior (TA) and soleus (SOL) muscles of the cat, and examined under s everal loading conditions, Four different load types were used: free-l imb motion (no load), flywheel, and two pendulums, each with a differe nt lever arm, Three types of coactivation strategies were considered, The first coactivation strategy consisted of antagonist activity that decreased as the agonist activity increased, The second strategy consi sted of increasing antagonist activity with increasing agonist activit y, And, in the third strategy, antagonist coactivation decreased at lo w force levels, then increased at high force levels, The three strateg ies were evaluated based on the joint angle's peak-to-peak movement an d its ability to track a linear input command given by the correlation coefficient of the output signal versus linear input, Results showed that increasing antagonist activity resulted in decreasing peak-to-pea k;angle and a decreased signal tracking capability for each load condi tion, The latter, however, was not as obvious In the flywheel load (as compared with free-moving and pendulum conditions). A decreasing peak -to-peak torque for pendulum loads was also observed with increasing a ntagonist activity, In all loading conditions, maximal peak-to-peak an gle and torque were present when a moderate degree of antagonist activ ity was engaged, and signal tracking capability improved with earlier engagement of the antagonist muscles, It is suggested that strategies using a combination of low-level coactivation, as described in the phy siological literature and previous functional electrical stimulation ( FES) studies, could satisfactorily address the issues of controllabili ty and efficiency while maintaining long-term joint integrity.