Pre-cooling alters pacing profiles resulting in no additional benefit to 20-km self-paced maximal cycling time-trial performance in heat acclimated endurance athletes.

Objectives: To examine the effect of pre-cooling (PreC) on cycling time-trial (CTT) performance in heat, before and after heat acclimation (HA).

Design: Randomised crossover.

Methods: Ten trained/highly trained male cyclists and/or triathletes completed two 20-km CTT before (PreHA) HA training sessions (10 × 60 min intermittent-heat exposure protocol in 36 °C, 50-80 % relative humidity), and after (PostHA). No cooling (CON) or crushed-ice was ingested (i.e., PreC) 30 min prior to the CTTs. The first and final HA training sessions were matched and acted as heat stress tests for comparison.

Results: No meaningful direct relations were observed for 20-km CTT completion time between PostHA+PreC (2663 ± 307 s) and PostHA-CON (2671 ± 370 s; b = 37.81 [-109.98, 170.56]). Split times were faster in the first 12.5 km of the CTT in PostHA+PreC but slower across the rest of the CTT compared to PostHA-CON (b = -1.224 [-2.196, -0.157]). Core temperature was lower in PostHA-CON compared to PostHA+PreC (b = -0.02 [-0.04, -0.01]). No difference was observed for mean skin temperature (b = -0.16 [-0.27, -0.05]) and thermal sensation (b = -0.047 [-0.091, -0.003]) during the CTT.

Conclusions: Insufficient evidence exists to support a meaningful performance improvement in 20-km CTT in hot-humid conditions when PreC was applied to individuals who completed an HA regime. This may be attributed to the limited effect of PreC on thermal perception, potentially leading to decreased exercise intensity in the latter stages of the CTT as a strategy to mitigate heat gain. Additionally, sub-optimal pacing strategies resulting from PreC on individuals may explain the lack of additional benefit to performance.