Effects of active warm up on thermoregulation and intermittent-sprint performance in hot conditions

This study examined the effects of active warm up on thermoregulatory responses and intermittent-sprint cycle performance in hot conditions (35.5 +/- 0.6 degrees C, RH 48.7 +/- 3.4%). Eight trained mates performed a 36-min, intermittent-sprint test (IST) after no (WUP 0), 10-min (WUP 10) or 20-min warm up (WUP 20). The IST contained 2-min blocks consisting of a 4-s sprint, 100s active recovery and 20s passive rest. Twice during the IST, there was a repeated-sprint bout (RSB) comprising five, 2-s sprints separated by similar to 20s. There were no significant differences between trials for mean work (3870 +/- 757 versus 4028 +/- 562 versus 3804 +/- 494 J sprint(-1)), peak power (W) or work decrement (%). However, mean work was significantly less in RSB2 than RSB1 for WUP 20 only (P < 0.05). Plasma lactate was significantly higher after active warm up (WUP 20 = WUP 10 > WUP 0; P < 0.05), but not significantly different between conditions following either RSB. Recta[ temperature (T(re)) was significantly higher after active warm up (37.0 +/- 0.3 versus 37.3 +/- 0.3 versus 37.7 +/- 0.1 degrees C for WUP0, WUP10 and WUP20, respectively) and throughout the IST The longer active warm up resulted in a greater increase in T(re) and was associated with a decrease in short-term repeated-sprint ability (with incomplete recovery), but not prolonged, intermittent-sprint performance in the heat. As active warm up did not improve performance (<40 min), team-sport athletes may minimise changes in T(re) (and the likelihood of heat illness) by avoiding excessive warm up when competing in the heat. (C) 2007 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.