Ed McNeely- Peak Centre for Human Performance
Heat is a major limiting factor in endurance performances. It has been quite well established that as temperature increases so does marathon time. Over the past 5-10 years more and more attention has been paid to dealing with heat stress while training and competing. Ice vests have proven to be quite effective when worn for a period of time immediately prior to a race but are often impractical and quite expensive. There is evidence that consuming cold water can improve time to exhaustion and running performance compared to warm water (1). Recently this idea was taken a step further by a group of Australian researchers. Using a group of ten moderately trained recreational runners, they examined the effects of drinking a Slushie right before running compared to cold water. All subjects participated randomly in both trials, running as long as possible at their aerobic threshold in a warm environment of 34oC and 55% humidity. Before each run the subjects ingested 7.5g/kg of either a Slushie or the cold water. The temperature of the Slushie was -1oC and the cold water was 4oC. Both drinks contained a 5% carbohydrate solution. When the subjects consumed the Slushie they ran 19% longer than after consuming water. Both groups were equally hydrated at the start of their runs but the Slushie group had a lower rectal temperature. Interstingly the Slushie group maintained a lower body temperature for the first 30 minutes of their run but ended up with a higher temperature at exhaustion. The authors have suggested that the colder temperature of the Slushie may have decreased brain temperature and delayed the point where a critically high brain temperature causes fatigue, around 42oC. This study clearly shows that Slushies are performance enhancers when you are exercising in the heat. So next time you head off for a training session run by 7-11 or Mac’s Milk for a quick slushie, it will make those training sessions in the heat more tolerable and even improve your performance.
Lee JK, Shirreffs SM, Maughan RJ. Cold drink ingestion improves exercise endurance capacity in the heat. Med Sci Sports Exerc. 2008;40(9):1637–44
Siegel, R., J. Mate , M. B. Brearly, G. Watson, K. Nosaka, and P. B. Laursen. Ice Slurry Ingestion Increases Core Temperature Capacity and Running Time in the Heat. Med. Sci. Sports Exerc., Vol. 42, No. 4, pp. 717–725, 2010.
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