Training-related changes in the maximal rate of torque development and EMGactivity

This study monitored the effects of a short-term elbow flexor training prog ram on surface electromyographic (SEMG) spike activity. The experimental pa radigm consisted of three test sessions separated by 2-week intervals. At t he beginning of each session, participants (N=13) performed five maximal ef fort isometric contractions of the elbow flexors to serve as baseline. Afte r 5 min of rest, the participants then engaged in a 30-trial isometric fati gue protocol during which maximal elbow flexion torque was measured with a load-cell, and the maximal rate of change in the torque (d tau /dt(max)) wa s obtained from the differentiated torque-time curve. Bipolar electrodes we re used to monitor the SEMG spike activity of the biceps brachii, Mean spik e amplitude (MSA) and mean spike frequency (MSF) were calculated for the to rque development and constant-torque phases of the isometric contraction, t ermed Segment 1 and Segment 2, respectively. Mean power frequency (MPF) was also calculated for Segment 2. The five baseline contractions of the secon d and third sessions were compared with those of the first session and anal yzed for training-related changes. Training increased d tau /dt(max) but fa iled to change maximal elbow flexion torque or MSA. However, there was an i ncrease in the MSF during the torque development phase of the contraction ( Segment 1). Both MSA and MSF were greatest during the constant-torque phase of the isometric contraction (Segment 2), There was a strong, linear corre lation (r=0.90, P<0.05) between MSF and MPF during (Segment 2), We hypothes ize that the increase in d<tau>/dt(max) is due to enhanced motor-unit rate- coding. The demonstrated correlation between MSF and MPF measures will allo w investigators to use spike analysis to examine the frequency content of t he SEMG signal under non-stationary conditions. (C) 2001 Elsevier Science L td. All rights reserved.