Ice Slurry Ingestion Improves Subsequent Outdoor 10 km Running Performance in the Heat

Abstract

All previous studies on thermoregulation with the ingestion of a cold debt have been conducted in laboratory settings. PURPOSE: To investigate thermoregulatory responses and performance with the ingestion of ice slurry before an outdoor 10 km running time trial in the heat (mean ± SD; WBGT: 28.3 ± 0.5°C). METHODS: Thirteen healthy runners (nine males and four females) completed a full familiarisation run, followed by two experimental trials in a counterbalanced order, ingesting either 8 g/kg body mass of ice slurry or ambient temperature (30°C) drink before a 10 km run. Each run was preceded by a 15 min warm up session. All trials were conducted on an outdoor 400 m running track. Ambient temperature drinks were provided ad libitum approximately every 3 km of the race. An ingestible temperature capsule was consumed 8 to 17 h before all trials for measurement of gastrointestinal temperature (Tint) as an index of body core temperature. Chest temperature, heart rate, sweat rate, 200 m split times, and ratings of thermal sensation and perceived exertion were assessed. RESULTS: Twelve of the 13 runners ran faster (median: 0.9%; range: -3.6 to 2.4%) with ice slurry compared to ambient temperature drink. Before the run, Tint (n = 12) decreased by 0.5 ± 0.2°C with ice slurry compared to a reduction of 0.1 ± 0.2°C (P < 0.001) with ambient temperature drink. At the end of the run, Tint was higher with ice slurry (40.2 ± 0.6°C) compared to ambient temperature drink (39.9 ± 0.4°C; P = 0.05). Relative to the ambient temperature drink (0.9 ± 0.4), mean ratings of thermal sensation were lower during the cooling phase and for the first kilometer of the run following ice slurry ingestion (-1.2 ± 0.8; P < 0.001). Running pace was increased by 1.4 ± 0.3 s (P < 0.05) at every 200 m split for the final 2.4 km of the 10 km time trial with ice slurry. Chest temperature, heart rate, sweat rate and perceived exertion were similar (P > 0.05) during both trials. CONCLUSION: This is the first study describing the efficacy of ingesting ice slurry before an outdoor 10 km running time trial. Compared to the drink at ambient temperature, ice slurry decreased body core temperature before the run and increased running pace in the final quarter of the time trial. These findings enhance the ecological validity of ingesting ice slurry to improve subsequent performance in endurance events in the heat.