ACOUSTIC AND ELECTRICAL-ACTIVITIES DURING VOLUNTARY ISOMETRIC CONTRACTION OF BICEPS BRACHII MUSCLES IN PATIENTS WITH SPASTIC CEREBRAL-PALSY

This study was designed to compare electromyogram (EMG) and acoustic m yogram (AMG) recordings of biceps brachii muscles in patients with spa stic cerebral palsy (CP). The maximal voluntary contraction (MVC) in t he CP group was approximately one half of that of the normal group eve n after being normalized by the muscle cross-sectional area (CSA) (18. 6 +/- 5.9 kNm/m(2) in CP, 37.3 +/- 2.9 kNm/m(2) in normal). Both CP an d normal groups demonstrated a progressive increase in the root mean s quared values per unit muscle CSA in the EMG (RMS(EMG)/CSA) as well as in the AMG (RMS(AMG)/CSA) with increasing force up to 50% MVC. The in creasing magnitude of the RMS(EMG)/CSA with force was not significantl y different between two subject groups, However, all the levels of for ce resulted in significantly smaller RMS(AMG)/CSA in the CP group comp ared to the normal group, The ratios of RMS(AMG) to RMS(EMG) in the CP group (0.75 +/- 0.03 m/s(2)/mV) were significantly smaller than those in the normal group (1.37 +/- 0.07 m/s(2)/mV) at force levels above 3 0% MVC. These results suggest that motor disabilities in CP patients a re caused not only by primary neural impairment but also by secondary deterioration in muscular contractile properties, probably resulting f rom muscle fiber atrophy, This appears to be more selective in fast tw itch fibers. (C) 1996 John Wiley & Sons, Inc.