Pethick, JamieWhiteaway, KatherineWinter, Samantha LBurnley, Mark2021-09-142021-09-142018-11-28Pethick, J., Whiteaway, K, Winter, S.L. and Burnley, M. (2018) Prolonged depression of knee-extensor torque complexity following eccentric exercise. Experimental Physiology, 104(1), pp. 100-111.0958-067030485571 (pubmed)10.1113/ep087295http://hdl.handle.net/2436/624341This is an accepted manuscript of an article published by Wiley in Experimental Physiology, available online: https://doi.org/10.1113/EP087295 The accepted version of the publication may differ from the final published version.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.application/pdfencomplexityeccentricfatiguefractal scalingnon-linear dynamicsKneeMuscle, SkeletalKnee JointFemoral NerveHumansExerciseMuscle FatigueMuscle ContractionIsometric ContractionMaleJournal article1469-445XExperimental Physiology2021-09-09