title: Acute effects of dynamic exercises on the relationship between the motor unit firing rate and the recruitment threshold.
abstract: The aim of this study was to compare the acute effects of concentric versus eccentric exercise on motor control strategies. Fifteen men performed six sets of 10 repetitions of maximal concentric exercises or eccentric isokinetic exercises with their dominant elbow flexors on separate experimental visits. Before and after the exercise, maximal strength testing and submaximal trapezoid isometric contractions (40% of the maximal force) were performed. Both exercise conditions caused significant strength loss in the elbow flexors, but the loss was greater following the eccentric exercise (t=2.401, P=.031). The surface electromyographic signals obtained from the submaximal trapezoid isometric contractions were decomposed into individual motor unit action potential trains. For each submaximal trapezoid isometric contraction, the relationship between the average motor unit firing rate and the recruitment threshold was examined using linear regression analysis. In contrast to the concentric exercise, which did not cause significant changes in the mean linear slope coefficient and y-intercept of the linear regression line, the eccentric exercise resulted in a lower mean linear slope and an increased mean y-intercept, thereby indicating that increasing the firing rates of low-threshold motor units may be more important than recruiting high-threshold motor units to compensate for eccentric exercise-induced strength loss.
authors.affiliation: Department of Health and Exercise Science, 1401 Asp Ave. Room 104, University of Oklahoma, Norman, OK 73019, USA. Electronic address: xin.ye-1@ou.edu.
authors.forename: Xin
authors.initials: X
authors.lastname: Ye
authors.affiliation: Department of Health and Exercise Science, 1401 Asp Ave. Room 104, University of Oklahoma, Norman, OK 73019, USA.
authors.forename: Travis W
authors.initials: TW
authors.lastname: Beck
authors.affiliation: Health and Human Performance, Oklahoma State University, 198 Colvin Rec Center, Stillwater, OK 74078, USA.
authors.forename: Jason M
authors.initials: JM
authors.lastname: DeFreitas
authors.affiliation: Department of Health and Exercise Science, 1401 Asp Ave. Room 104, University of Oklahoma, Norman, OK 73019, USA.
authors.forename: Nathan P
authors.initials: NP
authors.lastname: Wages
mesh_terms: D000328:Adult; D001132:Arm / Q000502:physiology; D004550:Elbow / Q000502:physiology; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D016014:Linear Models; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000502:physiology*; D011999:Recruitment, Neurophysiological; D012044:Regression Analysis; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D055815:Young Adult
keywords: 2330; 2540; 4160; Concentric exercise; Eccentric exercise; Linear regression analysis; Motor unit firing rate; Recruitment threshold