SPECIAL COMMUNICATIONS: Letters to the Editor-in-Chief
The study by Lee et al. (2) shows that, compared with the ingestion of warm fluids (∼37°C) of similar volume, drinking cold fluids (4°C) enhanced endurance exercise by up to 23% during exercise at a fixed intensity in hot, humid conditions. Because the same volume of fluid was ingested in both conditions, the authors correctly conclude that the ingestion of cold fluid explained this difference. Notably, subjects ingesting cold fluid started exercise with a reduced rectal temperature (precooling). Terminal rectal temperatures were identical in both conditions. These findings raise two important questions: Was the extended endurance time due either to this precooling effect or to the continued ingestion of cold fluids during exercise? What causes termination of exercise at 39.5°C in both conditions even when the exercise durations were different?
We have previously shown that neither exercise performance nor the thermoregulatory response was different in subjects who drank either nothing or sufficient to prevent any weight loss during 1 h of high-intensity self-paced exercise in the heat (1). Subsequently, we showed that preexercise hyperhydration failed to influence exercise performance under similar conditions (5). These findings suggest that fluid ingestion alone plays little role in modifying the thermoregulatory response or in improving performance during exercise lasting approximately 1 h. Perhaps the ergogenic effect of cold drink ingestion in the study of Lee et al. (2) was due either to a precooling effect or to the beneficial thermoregulatory effects of cold drink ingestion during exercise.
We have previously proposed that the ingestion of cold drinks during exercise at a fixed intensity might alter the rate of increase in body temperature so that this beneficial thermoregulatory effect might improve exercise performance (3,4). Data from our previous study (1) (Fig. 1, top) show that the rate of rise in body temperature was almost identical (range = 1.1-1.4°C·h−1) when subjects performed self-paced exercise when ingesting either cold fluids (4°C) or no fluids in both warm and moderate conditions. In contrast, the data of Lee et al. (2) reveal that the rate of rise in body temperature was slower when cold fluids were ingested during exercise (Fig. 1, bottom).
These data suggest that the ingestion of cold drinks before and during exercise may enhance performance either by a precooling effect or by reducing the rate at which body heat accumulates during exercise. We (6,8,9) and others (7) have shown that, during self-paced exercise, the body regulates its performance in an anticipatory manner to ensure that the rate of heat accumulation, and hence, the rate of rise in body temperature, is controlled. The findings of Lee et al. (2) are also compatible with this explanation.
Frank E. Marino
School of Human Movement Studies
Charles Sturt University
Bathurst NSW, Australia
Timothy D. Noakes
Department of Human Biology
University of Cape Town
1. Kay D, Marino FE. Failure of fluid ingestion to improve self-paced exercise performance in moderate-to-warm humid environments. J Therm Biol
2. Lee JKW, Shirreffs SM, Maughan RJ. Cold drink ingestion improves exercise endurance capacity in the heat. Med Sci Sports Exerc
3. Marino F, Kay D, Serwach N. Exercise time to fatigue and the critical limiting temperature: effect of hydration. J Therm Biol
4. Marino FE. Evidence for anticipatory regulation mediated by drink temperature during fixed intensity exercise in the heat. Exp Physiol
5. Marino FE, Kay D, Cannon J. Glycerol hyperhydration fails to improve endurance performance and thermoregulation in humans in a warm humid environment. Pflugers Arch
6. Marino FE, Lambert MI, Noakes TD. Superior performance of African runners in warm humid but not in cool environmental conditions. J Appl Physiol
7. Tatterson AJ, Hahn AG, Martin DT, Febbraio MA. Effect of heat and humidity on time trial performance in Australian national team road cyclists. J Sci Med Sport
8. Tucker R, Marle T, Lambert EV, Noakes TD. The rate of heat storage mediates an anticipatory reduction in exercise intensity during cycling at a fixed rating of perceived exertion. J Physiol (Lond)
9. Tucker R, Rauch L, Harley YXR, Noakes TD. Impaired exercise performance in the heat associated with an anticipatory reduction in skeletal muscle recruitment. Pflugers Arch