Prolonged depression of knee‐extensor torque complexity following eccentric exercise

Abstract

New Findings What is the central question of this study?Does eccentric exercise leading to prolonged knee‐extensor torque depression also result in a prolonged loss of knee‐extensor torque complexity? What is the main finding and its importance?The recovery of the loss of torque complexity after eccentric exercise took 24 h, whereas after acute muscle fatigue it took 10 min. The depression of torque complexity after eccentric exercise was prolonged. Abstract Neuromuscular fatigue reduces the temporal structure, or complexity, of muscle torque output. Exercise‐induced muscle damage reduces muscle torque output for considerably longer than high‐intensity fatiguing contractions. We hypothesized that muscle‐damaging eccentric exercise would lead to a persistent decrease in torque complexity, whereas fatiguing exercise would not. Ten healthy participants performed five isometric contractions (6 s contraction, 4 s rest) at 50% maximal voluntary contraction (MVC) before, immediately after and 10, 30 and 60 min and 24 h after eccentric (muscle‐damaging) and isometric (fatiguing) exercise. These contractions were also repeated 48 h and 1 week after eccentric exercise. Torque and surface EMG signals were sampled throughout each test. Complexity and fractal scaling were quantified using approximate entropy (ApEn) and the detrended fluctuation analysis α exponent (DFA α). Global, central and peripheral perturbations were quantified using MVCs with femoral nerve stimulation. Complexity decreased after both eccentric [ApEn, mean (SD), from 0.39 (0.10) to 0.20 (0.12), P < 0.001] and isometric exercise [from 0.41 (0.13) to 0.09 (0.04); P < 0.001]. After eccentric exercise, ApEn and DFA α required 24 h to recover to baseline levels, but after isometric exercise they required only 10 min. The MVC torque remained reduced [from 233.6 (74.2) to 187.5 (64.7) N m] 48 h after eccentric exercise, with such changes evident only up to 60 min after isometric exercise [MVC torque, from 246.1 (77.2) to 217.9 (71.8) N m]. The prolonged depression in maximal muscle torque output is therefore accompanied by a prolonged reduction in torque complexity.

Exercise Fatigue Detection Algorithm Based on Video Image Information Extraction

“…Relevant scholars collected the ECG and EMG signals of the experimenters in the exercise and fitness process, and analyzed the characteristics of the signals in the time domain and frequency domain respectively, and found the true characteristic indicators that reflect sports fatigue, and used Hidden Markov Model (HMM) to construct the HMM sports fatigue multi-classification model based on bioelectric signal [29]. Deep neural network can model multi-level fully connected network structure according to actual needs [30]- [32]. It has rich hierarchical structure and strong learning ability, which overcomes the limitations of pattern recognition.…”

Individualized Whole-Body Vibration: Neuromuscular, Biochemical, Muscle Damage and Inflammatory Acute Responses

“…57 Consequently, the decrease in contribution to force production from some damaged motor units is compensated for by means of increased recruitment and rate coding, as evidenced by the EMG amplitude increase, to achieve the required level of torque. 58 The decrease in maximal forcegenerating capacity after exercise-induced muscle damage persists for several days, while after either isometric or concentric exercises, it recovers almost completely within 10 to 60 minute. 58 Since WBV involves a stretch-shortening cycle (SSC), 1,54,55 it is not surprising that the eccentric component of the SSC muscle action causes muscle damage.…”

“…58 The decrease in maximal forcegenerating capacity after exercise-induced muscle damage persists for several days, while after either isometric or concentric exercises, it recovers almost completely within 10 to 60 minute. 58 Since WBV involves a stretch-shortening cycle (SSC), 1,54,55 it is not surprising that the eccentric component of the SSC muscle action causes muscle damage.…”

Physiological complexity: influence of ageing, disease and neuromuscular fatigue on muscle force and torque fluctuations

“…In this study, a fatigue‐induced loss of complexity was only observed during contractions above the critical torque, suggesting that peripheral fatigue is a prerequisite for such losses. (b) Long‐lasting peripheral derangements wrought by eccentric contractions depressed torque complexity for more than 60 min, whereas complexity following isometric contractions recovered within 10 min of task failure (TF; Pethick et al., 2019b). (c) The influence of caffeine administration on the progressive loss of torque complexity (Pethick et al., 2018b).…”

“…Further research has demonstrated differing recovery kinetics of muscle torque complexity following fatiguing isometric exercise and muscle damaging eccentric exercise that reduced MVC torque to the same extent (Pethick et al., 2019b). Following fatiguing isometric exercise, recovery of muscle torque complexity was complete 10 min after the cessation of exercise.…”