title: Duration-dependant response of mixed-method pre-cooling for intermittent-sprint exercise in the heat.
abstract: This study examined the effects of pre-cooling duration on performance and neuromuscular function for self-paced intermittent-sprint shuttle running in the heat. Eight male, team-sport athletes completed two 35-min bouts of intermittent-sprint shuttle running separated by a 15-min recovery on three separate occasions (33°C, 34% relative humidity). Mixed-method pre-cooling was completed for 20 min (COOL20), 10-min (COOL10) or no cooling (CONT) and reapplied for 5-min mid-exercise. Performance was assessed via sprint times, percentage decline and shuttle-running distance covered. Maximal voluntary contractions (MVC), voluntary activation (VA) and evoked twitch properties were recorded pre- and post-intervention and mid- and post-exercise. Core temperature (T (c)), skin temperature, heart rate, capillary blood metabolites, sweat losses, perceptual exertion and thermal stress were monitored throughout. Venous blood draws pre- and post-exercise were analyzed for muscle damage and inflammation markers. Shuttle-running distances covered were increased 5.2 ± 3.3% following COOL20 (P < 0.05), with no differences observed between COOL10 and CONT (P > 0.05). COOL20 aided in the maintenance of mid- and post-exercise MVC (P < 0.05; d > 0.80), despite no conditional differences in VA (P > 0.05). Pre-exercise T (c) was reduced by 0.15 ± 0.13°C with COOL20 (P < 0.05; d > 1.10), and remained lower throughout both COOL20 and COOL10 compared to CONT (P < 0.05; d > 0.80). Pre-cooling reduced sweat losses by 0.4 ± 0.3 kg (P < 0.02; d > 1.15), with COOL20 0.2 ± 0.4 kg less than COOL10 (P = 0.19; d = 1.01). Increased pre-cooling duration lowered physiological demands during exercise heat stress and facilitated the maintenance of self-paced intermittent-sprint performance in the heat. Importantly, the dose-response interaction of pre-cooling and sustained neuromuscular responses may explain the improved exercise performance in hot conditions.
authors.affiliation: School of Human Movement Studies, Charles Sturt University, Panorama Avenue, Bathurst, NSW 2795, Australia. gminett@csu.edu.au
authors.forename: Geoffrey M
authors.initials: GM
authors.lastname: Minett
authors.forename: Rob
authors.initials: R
authors.lastname: Duffield
authors.forename: Frank E
authors.initials: FE
authors.lastname: Marino
authors.forename: Marc
authors.initials: M
authors.lastname: Portus
mesh_terms: D000328:Adult; D054874:Athletic Performance / Q000502:physiology*; D001831:Body Temperature / Q000502:physiology*; D003080:Cold Temperature; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D005082:Physical Exertion; D012420:Running / Q000502:physiology*