Search

The aim of this study was to examine the effects of endurance training and endurance- based tapering on fatigue resistance of rat skeletal muscles. The rats were divided into one of five different groups: an agematched sedentary group: the first trained group which was subjected to a 10-wk endurance training: the second trained group which continued endurance training for additional 10 days after the 10-wk training: the third trained group which remained sedentary for 10 days after the 10-wk training: the fourth trained group which underwent a taper program (an unaltered-intensity, reducedvolume taper) for 10 days after the 10-wk training. Following each treatment, measures of force output and biochemical analyses were performed on gastrocnemius muscles. Fatigue resistance and the activity of citrate synthase were increased by the 10-wk training, but unaltered by three treatments after the 10-wk training (additional training, detraining or tapering). Training brought about the exchange of myosin heavy chain (MHC) isoforms in order of MHC Ilb-MHCIId/x--?MHCIIa whereas detraining caused the exchange from MHCIIa to MHCIId/x. Training resulted in reductions in the Ca2+ sequestering ability of sarcoplasmic reticulum (SR) and detraining returned the reduced ability to pre-training levels. The present results indicate that fatigue resistance of intact whole muscle is improved by training but not, at least, by the tapering protocol used in this study and suggest that enhancement of oxidative potential contributes to improved fatigue resistance, whereas muscle fiber transitions from type IID/X to 1IA fibers or decreases in the SR Ca2+ sequestering ability do not. [ABSTRACT FROM AUTHOR]