Control Entropy of mechanomyogram (MMG) and electromyogram (EMG) during fatiguing isometric muscle actions

Abstract

The purpose of this study was to determine if Control Entropy (CE) of MMG and EMG would decline during fatiguing isometric muscle actions. Procedures were approved by the Hope HSRB. Subjects performed one isometric leg extension (30° flexion) at the 1‐RM of the non‐dominant leg to volitional fatigue. MMG and EMG signals were recorded from the vastus medialis (VM) and rectus femoris muscles (RF) using commercial software (Biopac Systems, CA). The effort was divided into epochs (10% of time‐to‐fatigue) and mean and peak‐to‐peak (P‐P) amplitude MMG and EMG data were analyzed using repeated measures ANOVA (α=0.05). CE was calculated in Matlab (Mathworks, MA) using 2 and 8 bit partitions, and varying window lengths according to the following equation: CEKS[x(t)] =hKS[sign(dx/dt(t))]. P‐P amplitude of VM‐MMG and RF‐EMG declined (p<0.05), while RF‐MMG (p=0.58) trended lower over time. Mean amplitude of VM‐EMG declined (p<0.05). CE of the MMG declined over the course of the effort for males, but not for females. When accounting for gender, a significant effect was observed for P‐P of VM .MMG, RF‐EMG and mean VM‐EMG. In addition, CE of EMG exhibited an unexpected response whereby it increased at the onset of the muscle action. These results support previous reports of a differential MMG response in males vs females. The attenuated CE response of MMG in females vs. males may shed light on the nature of this difference between genders.