Short-term training, muscle glycogen, and cycle endurance

The objective of this study was to test the hypothesis that the increased glycogen concentration found in the working muscles following short-term training would result in an increase in endurance performance. Endurance performance was examined in 8 active but untrained males who cycled until fatigue at 65% VO2max prior to and following 3 consecutive days of training. Training consisted of cycling for 2 hrs a day at the same power output used in the prolonged fatigue trials. A 39% increase in cycle time, from 103 +/- 7.7 to 143 +/- 14 min (p < 0.05), was observed following training. At fatigue prior to training, glycogen concentration in the vastus lateralis muscle was depleted by 75% (317 +/- 17 to 78.8 +/- 32 mmol.glucosyl units .kg-1 d.w). Following training, glycogen concentration at a comparable work time was 2.3 times higher. The elevated glycogen level following training was due both to higher glycogen at rest and during exercise. The energy cost of the activity as measured by the VO2 at selected intervals was unchanged with training. No change (p > 0.05) in exercise time was observed in a control group who were subjected to similar exercise protocols approximately 1 to 2 weeks apart. It is concluded that short-term training at least in untrained individuals (VO2max averaging 43.6 +/- 2.9 ml.kg-1.min-1) substantially elevates submaximal exercise tolerance and that the increase in resistance to fatigue is related to the elevated availability of glycogen.