Hypervolemia and cycling time trial performance

Ten experienced cyclists rode three simulated time trials to determine whether hypervolemia was associated with improvements in cycling time trial performance. The conditions were: exercise-induced hypervolemia (ExH), dextran-induced hypervolemia (DxH), and euvolemia (Eu). ExH was induced by 3 d of submaximal cycling lasting an average of 92.9 min at an average relative intensity of 68%. DxH was induced by acute plasma volume expansion with 400 +/- 121 ml of a 6% dextran solution. Compared with Eu, ExH and DxH were associated with 9.4% and 8.7% elevations in blood volume as well as 11.1% and 12.4% elevations in plasma volume, respectively. Performance was significantly improved (P < 0.05) (i.e., target work goal reached earlier) during ExH (81.41 +/- 5.52 min) and DxH(81.36 +/- 5.06 min) than during Eu (90.87 +/- 5.27 min). Average power was significantly higher during E x H (246 +/- 13 W) and DxH (245 +/- 14 W) than during Eu (221 +/- 15 W). There were no significant differences in performance time or average power between the two hypervolemic conditions. Average sweat rates were significantly elevated during ExH (22.6 +/- 1.4 ml.min-1) and DxH (22.2 +/- 1.6 ml.min-1) than during Eu (20.4 +/- 1.7 ml.min-1). Rectal temperatures rose from approximately 37.2-39.2 degrees C during each time trial but there were no significant differences in T(re) between trials. In conclusion, hypervolemia, whether induced by short-term training or dextran-infusion, had a beneficial effect on performance and average power during simulated time trials lasting approximately 90 min. These improvements in performance were related to hypervolemia rather than other short-term training adaptations.