Effect of practical precooling on neuromuscular function and 5 km time-trial performance in hot, humid conditions amongst male, well-trained runners Running Head Title: Practical Precooling, Muscle Function and Endurance Performance

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 male, well-trained runners completed three randomized time-trials in 32.2 ± 0.8°C, 48.6 ± 6.7% relative humidity. A 30-min warm-up was completed with no cooling (Control), precooling via 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 to Control (1407 ± 80 vs. 1492 ± 88 s; P < 0.05), but not in Vest (1444 ± 7 s; 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 to Control. Maximum voluntary force, voluntary activation, muscle contractility and membrane excitability were not different after exercise or between conditions. After 10 min during the warmup, skin temperature was lower in Vest and Packs compared to 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.