Volume-Dependent Response of Precooling for Intermittent-Sprint Exercise in the Heat

MINETT, G. M., R. DUFFIELD, F. E. MARINO, and M. PORTUS. Volume-Dependent Response of Precooling for Intermittent-Sprint Exercise in the Heat. Med. Sci. Sports Exerc., Vol. 43, No. 9, pp. 1760-1769, 2011. Purpose: This study aimed to assess the effects of precooling volume on neuromuscular function and performance in free-paced intermittent-sprint exercise in the heat. Methods: Ten male, team-sport athletes completed four randomized trials involving an 85-min free-paced intermittent-sprint exercise protocol in 33 degrees C +/- 33% relative humidity. Precooling sessions included whole body (WB), head + hand (HH), head (H), and no cooling (CONT) applied for 20 min before exercise and 5 min during exercise. Maximal voluntary contractions were assessed before and after intervention and during and after exercise. Exercise performance was assessed with sprint times, percent decline and distances covered during free-paced bouts. Measures of core (T(c)) and skin (T(sk)) temperatures, HR, perceptual exertion, and thermal stress were monitored throughout. Venous and capillary blood samples were analyzed for metabolite, muscle damage, and inflammatory markers. Results: WB precooling facilitated the maintenance of sprint times during the exercise protocol with reduced percent decline (P = 0.04). Mean and total hard running distances increased with precooling 12% compared with CONT (P < 0.05); specifically, WB was 6%-7% greater than HH (P = 0.02) and H (P = 0.001), respectively. No change was evident in mean voluntary or evoked force before to after exercise with WB and HH cooling (P > 0.05). WB and HH cooling reduced T(c) by 0.1 degrees C-0.3 degrees C compared with other conditions (P < 0.05). WB T(sk) was suppressed for the entire session (P = 0.001). HR responses after WB cooling were reduced (P = 0.05; d = 1.07) compared with CONT conditions during exercise. Conclusions: A relationship between precooling volume and exercise performance seems apparent, as larger surface area coverage augmented subsequent free-paced exercise capacity, in conjunction with greater suppression of physiological load. Maintenance of maximal voluntary contraction with precooling despite increased work output suggests the role of centrally mediated mechanisms in exercise pacing regulation and subsequent performance.