This study investigated whether torso and thigh precooling during a warm-up effects neuromuscular function and 5-km time-trial performance in hot, humid conditions. Eight well-trained male runners completed 3 randomized time-trials in 32.2 ± 0.8° C and 48.6 ± 6.7% relative humidity. A 30-minute warm-up was completed with no cooling (Control), precooling by an ice vest (Vest), or ice packs covering the thighs (Packs). Before the warm-up and after the time-trial, supramaximal femoral nerve stimulation was delivered during and following maximal isometric contractions. Core and skin temperature, heart rate, and perceptual ratings were recorded before and during the warm-up and time-trial. Overall performance time was improved in Packs compared with Control (1,407 ± 80 seconds vs. 1,492 ± 88 seconds; p = 0.05) but not in Vest (1,444 ± 71 seconds; p > 0.05). In Packs, a higher exercise intensity (p = 0.05) and less cumulative time (p < 0.01) were evident during the last kilometer compared with Control. Maximum voluntary force, voluntary activation, muscle contractility, and membrane excitability were not different after exercise or between conditions. Ten minutes after the warm-up, skin temperature was lower in Vest and Packs compared with Control (p < 0.01). Thermal strain and body heat content change was lower in Vest and Packs, respectively (p = 0.05). Findings indicate that torso and thigh precooling during a warm-up reduces thermoregulatory strain. However, thigh opposed to torso precooling provides greater performance improvements. Neuromuscular function did not aid performance, indicating that transient changes in afferent feedback and muscle recruitment may enhance endurance trial performance.
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