Effect of Curare on Interrelationships of Force, EMG, and Joint Position for Isometric Contractions of Quadriceps Femoris in Man

Abstract

<p> The interrelationship of force, surface elecrograms (EMG) and joint position for static voluntary contractions of Quadriceps Femoris muscle group in man were investigated before and during partial curarization induced by d-tubocurarine. </p> <p> Four normal male volunteers were studied. Each performed a series of brief isometric contractions (by extension of the lower leg against resistance) at different levels of force and at three knee-joint positions while lying in the supine position. All series were repeated for both a normal state and a partially paralyzed state under the :influence of curare. Torque generated about the knee-joint was measured with a Cybex isokinetic system and the nyoelectric activity of three quadriceps muscles was monitored using bipolar surface electrodes. </p> <p> Traditional parameters of nyoelectric activity (mean-rectified-EMG [MRE], and root-mean-squared-DG [RMSE]) were calculated using a minicomputer (PDPll/34), which had also acquired and processed the data. In addition, EMG power spectra were computed by Fast Fourier Transform techniques in an attempt to provide further insight into the effects of curare on human muscle. </p> <p> In order to provide a basis for comparison of the normal state with the parially curarized state, force-EMG relationships were computed for each subject, muscle, knee-joint angle, and condition. Statistical methods (three-way ANOVA' s) were then employed to both quantify any differences that may have existed between the two states and to identify sources of differences within each state. A similar statistically- based comparison of the power spectra was undertaken utilizing several indices that described the shape of the spectra. A general description of the activities of the quadriceps femoris muscles followed after collating all the information that the surface DIG provided in conjunction with the external forces measured. </p> <p> It was concluded that curare did not have any significant effects on the force-EMG relationship. There appeared to be a slight effect of curare on the power spectra however, with a general trend of increasing lower frequency power. The greatest source of variation of force-EMG relationships and power spectra was attributed to the position of the knee-joint. </p>