Linear And Control Entropy Analysis Of Electromyography And Mechanomyography Signals During The Wingate Anaerobic Test

Abstract

PURPOSE: Tools from non-linear dynamical systems analysis may provide unique insight into the nature of fatigue during maximal exercise. Control entropy (CE) is a novel method to quantify the complexity of non-linear dynamic physiological signals and is indicative of control systems constraints. Therefore, the effects of fatigue on surface elecrtromyography (SEMG) and mechanomyography (MMG) were studied during the Wingate anaerobic test (WAnT) using CE analysis. METHODS: Twelve trained (6 M / 6 F) intercollegiate athletes volunteered to participate in procedures approved by the Hope College HSRB. MMG and SEMG of the rectus femoris (RF) and vastus medialis (VM) muscles of the dominant leg were recorded using accelerometers (ACC, ADXL330, Analog Devices, Inc., Norwood, MA) and surface electrodes. Measurements collected at a rate of 1000 Hz were amplified and recorded using Biopac (GA) EM100C, MP150 and AcqKnowledge v3.8.2 software, respectively. Participants performed a 30-second WAnT on a Lode Excalibur cycle egometer at 0.075 kp/kg of body weight. Linear comparisons of changes in the mean amplitude, peak-peak amplitude, and mean power density for both the MMG and EMG signals were made using repeated measures ANOVA (a ≤0.05). CE of raw MMG and SEMG signals were calculated and tested for significance using Matlab (The Mathworks, MA). RESULTS: Significant differences were observed between genders (p < 0.05); and there were significant effects of time (VM; RF) for mean MMG (p < 0.001), mean VM SEMG (p < 0.05), p-p MMG (p < 0.001), and p-p SEMG (p < 0.05). Fatigue Index (FI) calculations for MMG-FI and WAnT-FI (0.826 ± 0.010 and 0.491 ± 0.192, respectively) revealed a moderately high correlation (r = 0.725, p = 0.012). CE increased significantly in both MMG and EMG at the start of the WAnT. CE of MMG remained elevated for duration, while EMG declined as fatigue ensued. CONCLUSIONS: SEMG and MMG signals reflect the changes in power output seen in the WAnT. These may provide supplemental information in assessing anaerobic power. In particular, changes in CE indicate that constraints are reduced in both neurological and muscular system components during the WAnT and may provide unique insight into the nature of fatigue from supramaximal exercise.