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

Introduction Warm up is a widely accepted practice preceding nearly every athletic event. However, while active warm up has been reported to improve long-term (> 5 min) performance, active warm up may have a detrimental effect if it causes a significant decrease in heat-storage capacity and the earlier attainment of a high rectal temperature (Tr). The purpose of the present study was to determine the effects of an active warm up on thermoregulatory responses and repeated-sprint performance in hot, ambient conditions. Methods Eight male, team-sport athletes (mean * SD: age: 23.4 + 6.2 y, mass: 76.8 + 7.7 kg, VO2max: 59.9 + 8.0 mL·kg-1·min-1) performed a repeated sprint test (RST) for 36 min in hot ambient conditions (35.5 + 0.6 oC, RH 48.7 + 3.4%) after no warm up (WUP 0), 10-min warm up (WUP 10) or 20-min warm up (WUP 20). Based on a motion analysis of international men’s field hockey (2), the RST was designed to mimic one half of a typical team-sport game. The protocol was divided into ~ 2-min blocks consisting of a 4-s sprint, 100 s active recovery (35% VO2max) and 20 s passive rest. On two occasions during the 36-min protocol, there was a repeated-sprint bout (RSB) comprising five, 2-s sprints, where the active recovery between successive sprints was ~ 20 s. Results There were no significant differences between conditions for mean work (kJsprint-1; Fig 1.), peak power (W) or work decrement (%) during the RST. However, the mean work performed was significantly less in RSB2 than RSB1 for WUP 20 only (P<0.05). While blood lactate concentration was significantly higher after active warm up (WUP 20 = WUP 10 > WUP 0; P<0.05), there were no significant differences between conditions following either RSB. Tr was also significantly higher after active warm up (WUP 20 > WUP 10 > WUP 0; P<0.05) and these differences were maintained throughout the RST (Fig 2). Discussion Although active warm up resulted in a greater increase in Tr, it did not affect repeated-sprint performance in the heat in trained team-sport athletes. Despite similar changes in Tr, it has previously been reported that active warm up decreases intermittent exercise time to exhaustion in healthy males (1). However, the test used did not simulate team-sport performance and nor were the subjects team-sport athletes. It therefore appears that small increases in Tr do not affect repeated-sprint performance in trained team-sport athletes. However, as active warm up did not improve repeated-sprint performance (< 40 min), team sport athletes may be able to minimise changes in Tr (and the likelihood of heat illness) by avoiding excessive warm up when exercising in the heat. References 1. Gregson, W., et al. (2002). J. Sp. Sci., 20(1): 49-50. 2. Spencer, et al. (2002). J. Sci. Med. Sport. 5(4; Suppl): 102