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Muscle glycogen reduction in man: relationship between surface EMG activity and oxygen uptake kinetics during heavy exercise
Author(s) -
Osborne Mark A.,
Schneider Donald A.
Publication year - 2006
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2005.031450
Subject(s) - motor unit recruitment , chemistry , vastus medialis , glycogen , motor unit , electromyography , medicine , time trial , endocrinology , cardiology , heart rate , physical medicine and rehabilitation , biochemistry , anatomy , blood pressure
The purpose of this study was to determine whether muscle glycogen reduction prior to exercise would alter muscle fibre recruitment pattern and change either on‐transient O 2 uptake () kinetics or the slow component. Eight recreational cyclists (, 55.6 ± 1.3 ml kg −1 min −1 ) were studied during 8 min of heavy constant‐load cycling performed under control conditions (CON) and under conditions of reduced type I muscle glycogen content (GR). was measured breath‐by‐breath for the determination of kinetics using a double‐exponential model with independent time delays. was higher in the GR trial compared to the CON trial as a result of augmented phase I and II amplitudes, with no difference between trials in the phase II time constant or the magnitude of the slow component. The mean power frequency (MPF) of electromyography activity for the vastus medialis increased over time during both trials, with a greater rate of increase observed in the GR trial compared to the CON trial. The results suggest that the recruitment of additional type II motor units contributed to the slow component in both trials. An increase in fat metabolism and augmented type II motor unit recruitment contributed to the higher in the GR trial. However, the greater rate of increase in the recruitment of type II motor units in the GR trial may not have been of sufficient magnitude to further elevate the slow component when was already high and approaching .