title: History dependence of the electromyogram: Implications for isometric steady-state EMG parameters following a lengthening or shortening contraction.
abstract: Residual force enhancement (RFE) and force depression (FD) refer to an increased or decreased force following an active lengthening or shortening contraction, respectively, relative to the isometric force produced at the same activation level and muscle length. Our intent was to determine if EMG characteristics differed in the RFE or FD states compared with a purely isometric reference contraction for maximal and submaximal voluntary activation of the adductor pollicis muscle. Quantifying these alterations to EMG in history-dependent states allows for more accurate modeling approaches for movement control in the future. For maximal voluntary contractions (MVC), RFE was 6-15% (P<0.001) and FD was 12-19% (P<0.001). The median frequency of the EMG was not different between RFE, FD and isometric reference contractions for the 100% and 40% MVC intensities (P>0.05). However, root mean square EMG (EMGRMS) amplitude for the submaximal contractions was higher in the FD and lower in the RFE state, respectively (P<0.05). For maximal contractions, EMGRMS was lower for the FD state but was the same for the RFE state compared to the isometric reference contractions (P>0.05). Neuromuscular efficiency (NME; force/EMG) was lower in the force depressed state and higher in the force enhanced state (P<0.05) compared to the isometric reference contractions. EMG spectral properties were not altered between the force-enhanced and depressed states relative to the isometric reference contractions, while EMG amplitude measures were.
authors.affiliation: Faculty of Kinesiology, Human Performance Laboratory, University of Calgary, 2500 University Dr. NW, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Alexis A
authors.initials: AA
authors.lastname: Jones
authors.affiliation: Faculty of Kinesiology, Human Performance Laboratory, University of Calgary, 2500 University Dr. NW, Calgary, Alberta T2N 1N4, Canada; Dept. of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Power
authors.affiliation: Faculty of Kinesiology, Human Performance Laboratory, University of Calgary, 2500 University Dr. NW, Calgary, Alberta T2N 1N4, Canada. Electronic address: wherzog@ucalgary.ca.
authors.forename: Walter
authors.initials: W
authors.lastname: Herzog
mesh_terms: D000328:Adult; D004576:Electromyography / Q000379:methods*; D005260:Female; D006225:Hand / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D055815:Young Adult
keywords: Concentric; Eccentric; Electromyography (EMG); Force depression; Muscle; Potentiation; Power density spectrum; Residual force enhancement