Precooling leg muscle prior to and during warm-up for intermittent sprint exercise in the heat

Introduction Twenty minutes of thigh muscle precooling has shown to improve intermittent sprint performance in the heat by ~4% (Castle et al. 2006). Central fatigue mechanisms have been proposed for reduced performance in prolonged activities in the heat in comparison to a temperate environment (Kay et al. 2001). Precooling may influence central activation of exercising muscles, leading to improved self-paced endurance exercise (Duffield et al. 2010). The influence of a warm-up following precooling, including cooling during this period has however, received little attention. This study investigated the effect of precooling and warm-up cooling of the thigh on central activation of the rectus femoris muscle during intermittent sprint exercise in the heat. Methods Seven males performed four cycling intermittent sprint protocols (CISP) in hot, humid (30°C, 50% relative humidity) conditions following 20 minutes localised thigh precooling (PRE), 7 minutes warm-up cooling (W-UP), precooling and warm-up cooling (COMB) or no cooling (CON) in a randomised order. The CISP consisted of twenty, 2 minute periods (10s passive rest, 5s maximal sprint, 105s active recovery). Maximum voluntary contraction of the rectus femoris muscle was performed to normalise sprint EMG data. Muscle temperature of the vastus lateralis (Tm) was also measured. Results Average peak power output (PPO) showed an 8% increase in PRE (982±166W) over CON (911±161W P<0.05). No such increase was evident for COMB or W-UP (928±161W, 930±160W respectively P>0.05). Resting Tm (33.5±2.4°C) was reduced by precooling in PRE and COMB to 19.3±2.1°C and 20.2±2.9°C respectively (P<0.05). Prior to the CISP, Tm was 35.1±1.8°C, 33.3±2.9°C, 31.3±2.7°C* and 29.9±1.6°C* for CON, PRE, W-UP and COMB respectively (*P<0.05 in comparison to control). There was no difference in post CISP Tm across all conditions (P>0.05). Localised thigh cooling did not influence central activation of the rectus femoris during the CISP for any condition. Discussion Twenty minutes of precooling the leg muscles improved intermittent sprint performance in the heat (PRE) by 8%, supporting findings of Castle et al. (2006), and occurred without a concomitant increase in EMG activity. Continuing cooling in the warm-up (COMB) did not further enhance intermittent sprint exercise in the heat but did blunt the rise in Tm seen in PRE. Precooling followed by a warm-up (PRE) improves the Temperature-Force relationship of muscle and enhances intermittent sprint exercise in the heat. References Castle P, Macdonald A, Philp A, Webborn A, Watt P, Maxwell, N. 2006. J Appl Physiol, 100, 1377-84. Duffield R, Green R, Castle P, Maxwell N. 2010. Med Sci Sports Exerc, 42, 577-84. Kay D, Marino F, Cannon, J, St Clair Gibson A, Lambert M, Noakes, T. 2001. Eur J Appl Physiol, 84, 115-21