EMG-FORCE RELATION IN DYNAMICALLY CONTRACTING CAT PLANTARIS MUSCLE

The purpose of this study was to revisit the electromyographical (EMG) -force relationship of dynamically contracting muscles using direct me asurements of EMG and force in cat hindlimb muscles during locomotion. EMG signals were recorded from the plantaris muscle using bipolar ind welling wire electrodes, and the corresponding forces were measured us ing a tendon force transducer. Force-time histories of cat plantaris m uscle were predicted by estimating selected force parameters from EMG and timing parameters, and then constructing two smoothly fitting quin tic spline functions from the estimated force parameters. The force pr edictions did not contain information on force-length or force-velocit y properties of the cat plantaris and did not use instantaneous contra ctile conditions as input. It was found that two smoothly fitting quin tic spline functions provided the required properties to approximate p lantaris force-time histories accurately, and approximations of the fo rce-time histories using EMG and timing parameters as input for the qu intic splines were good. The root mean square errors (RMS) of the pred icted compared to the actual plantaris forces were smaller than corres ponding results reported in the literature, even though the prediction model did not require the force-length-velocity properties or the ins tantaneous contractile conditions of the target muscles as input. From the results obtained in this study, it appears that force-time histor ies of the cat plantaris muscle during locomotion can be predicted ade quately from information obtained using EMG and video records, without information on either the force-length and force-velocity properties, or the instantaneous contractile conditions of the muscle. (C) 1998 E lsevier Science Ltd. All rights reserved.