Cooling before and during exercise in hot weather yields a positive, but moderate, improvement in an athlete's performance in stop-and-go and endurance exercise, but actually impairs performance in short-duration, high intensity exercise, especially when the active muscles are directly cooled, a review of the medical literature suggests. 
Reviewing 23 studies which investigated the effect of cooling administered either prior to or during exercise in hot weather (all involving trained, rather than elite athletes), researchers in the United Kingdom noted improvements in prolonged exercise performance or capacity as a result of pre-cooling using a variety of methods (water immersion, applying ice packs to the skin, wearing ice-cooling garments, cold air exposure, or a combination of these approaches) in all but one study.
Cooling during exercise performed in hot weather, the effect of which was investigated in six studies, such as via cold air exposure, cooling of the torso via an ice vest, and neck cooling using a cooling collar, also had a smaller positive effect on performance. although such cooling may be impractical (e.g. excess weight and skin irritation, and regulations of the sport).
"The effectiveness of the cooling intervention used either prior to or during exercise is dependent on the volume of cooling either prior to or during exercise," writes Dr. Christopher James Tyler of the Department of Life Sciences at the University of Roehampton in London, "and the extent of the thermal strain experienced."
The study was published online in the British Journal of Sports Medicine.
Advice for athletes
While the study found that optimal cooling strategies have yet to be identified for a range of sporting settings due to marked differences in cooling protocols and performance and capacity assessments investigated to date, Brendon P. McDermott, PhD, ATC, Assistant Professor/Clinical Coordinator in the Graduate Athletic Training Education Program at the University of Arkansas, offers the following tips about pre-cooling:
- For exercise lasting 30 to 45 minutes: research demonstrates that pre-cooling is beneficial for performance and keeping you cooler. Plus, it makes you feel better for about an hour, provided you cool enough prior to activity.
- For exercise lasting more than an hour: there is no safety, performance or perceptual difference when you've pre-cooled. There is potential that some modalities may be effective for cooling during a half-time scenario or periodically during breaks to keep body temperature down, but there is no convincing evidence yet to recommend a protocol.
- For intense exercise: there is a question whether pre-cooling may actually lead to a faster rise in core temperature. This occurs because we feel better after pre-cooling, and we're able to push harder in exercise, which produces more heat. Some studies show that body temperature following exercise was higher in those who cooled. So, we feel better, but our temperature is higher than we think. More research is needed on safety and to determine a pre-cooling protocol that can only benefit, rather than compromise, safety.
Why cooling works
Precooling is the most popular strategy to combat hypothermia. It is believed that precooling may benefit subsequent exercise in two ways: first, it can directly affect the physiological state of the body and enhance performance by lowering the thermal strain experienced by allowing an athlete to start exercise at a lower core temperature and/or attenuate the rate at which core temperature increases during exercise. Second, even if the magnitude of the cooling is not enough to have a direct effect on the athlete's physiological state, performance benefits may still occur, which may be due to an alteration in the level of perceived thermal strain experienced by the athlete during exercise (i.e. a placebo effect).
1. Tyler CJ, Sunderland C, Cheung SS. The effect of cooling prior to and during exercise performance and capacity in the heat: a met-analysis. Br J Sports Med 2013;doi:10.1136/bjsports-2012-091739 (epub August 14, 2013)
Posted September 9, 2013