caa a22 4500 469055588 CHVBK 20180323132842.0 cr unu---uuuuu 170328e19920701xx s 000 0 eng 10.1007/BF00636225 doi (NATIONALLICENCE)springer-10.1007/BF00636225 Modification of myo-electric power spectrum in fatigue from 15% maximal voluntary contraction of human elbow flexor muscles, to limit of endurance: reflection of conduction velocity variation and/or centrally mediated mechanisms? [Elektronische Daten] [Claes Krogh-Lund, Kurt Jørgensen] Summary: Isometric flexion of the right elbow at 15% of the maximal voluntary contraction (MVC) was maintained to the limit of endurance (elbow angle 135°). The surface electromyogram (EMG) of the brachioradialis (BR) and biceps brachii (BB) muscles was recorded for calculation of conduction velocity (CV) by the cross-correlation method, and determination of median frequency (fm) and root mean square (rms) amplitude. Perceived exertion was rated for both muscles, and heart rate and blood pressure were measured. The EMG of ten brief 15% MVC contractions distributed over a 30-min recovery period was also recorded. Eleven males in their twenties volunteered for the investigation. The average endurance time was 906 (SD 419) s. Mean CV for the unfatigued muscles was 4.2 (SD 0.41) m·s−1 (BR), and 4.3 (SD 0.29) m·s−1 (BB). The contraction caused a significant decrease in CV of BR (12%,P<0.001) whereas CV variation of BB remained insignificant. Concurrently the meanf m of both muscles dropped to approximately 66% of their initial values and their average rms amplitudes grew by approximately 380% (BR and BB:P<0.001, both parameters). The 1st min of recovery lowered the rms amplitudes by approximately 60% (BR and BB:P<0.01), while thef m increased to approximately 88% of the initial recording (BR,P<0.01; BB,P<0.05). The accompanying small increases in CV were beyond the level of significance. Over the next 29 min a significant parallel restitution inf m and CV took place; changes inf m evidenced a simple one to one reflection of relative CV variation. A similar uncomplicated linear causality between relative changes in CV andf m was hypothesized for the endurance contraction. Consequently, the 12% CV decrease of the BR accounted for only one-third of the fatigue inducedf m reduction of 33%, while two-thirds were assumed to be attributable to centrally mediated regulatory interventions in motor unit (MU) performance. Independent of contributions from the virtually unchanged CV, thef m of the BB muscle decreased by 35%; from one subject exhibiting a remarkably manifest burst-type pattern of MU activity it is argued that synchronization/grouping of MU firing predominantly determined the power redistribution in the BB spectrum. Springer-Verlag, 1992 Low-level isometric contraction nationallicence Localized muscle fatigue nationallicence Conduction velocity nationallicence Myo-electric power spectrum nationallicence Perceived exertion nationallicence Krogh-Lund Claes Danish Acoustical Institute, Lyngby, Denmark aut Jørgensen Kurt The August Krogh Institute, University of Copenhagen, Copenhagen, Denmark aut European Journal of Applied Physiology and Occupational Physiology Springer-Verlag 64/4(1992-07-01), 359-370 0301-5548 64:4<359 1992 64 421 https://doi.org/10.1007/BF00636225 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00636225 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Krogh-Lund Claes Danish Acoustical Institute, Lyngby, Denmark aut NATIONALLICENCE 700 1- Jørgensen Kurt The August Krogh Institute, University of Copenhagen, Copenhagen, Denmark aut NATIONALLICENCE 773 0- European Journal of Applied Physiology and Occupational Physiology Springer-Verlag 64/4(1992-07-01), 359-370 0301-5548 64:4<359 1992 64 421 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer