SPECIAL COMMUNICATIONS: Letters to the Editor-in-Chief
We appreciate the interest shown by Dr. Marino and Prof. Noakes in our study (5), and we are pleased to acknowledge that our findings may be consistent with their conclusion 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."
Dr. Marino and Prof. Noakes ask, "Was the extended endurance time due either to this precooling effect or to the continued ingestion of cold fluids during exercise?" We reported in our paper that, "the rate of rise [of core temperature] was similar in both trials," as would be expected when the power output was the same. This is contrary to the analysis of our data by Marino and Noakes (their Figure 1). The data are shown correctly in our Figure 1. It seems, perhaps unsurprisingly, that ingestion of 100 mL of cold fluid every 10 min during exercise was of less consequence than the preexercise ingestion of 900 mL of cold fluid: preexercise T re fell by 0.5°C when cold drinks were ingested but was unchanged by ingestion of warm drinks. As mentioned in our paper, consumption of cold drinks during exercise results in no meaningful difference in T re between trials, regardless of whether drinks are consumed as one large bolus at a single time point (4) or in smaller volumes at intervals during exercise (6).
Gonzalez-Alonso et al. (3) manipulated body heat content by preexercise water immersion: time to fatigue was inversely related to initial core temperature but the rate of heat storage was not different. In our study, we do not know what caused the termination of exercise on both trials at the same mean core temperature; however, although the mean core temperature attained at fatigue was the same on both trials (39.5°C), there was considerable interindividual variability. Figure 2 illustrates individual rectal temperature of our eight volunteers at exhaustion on the two trials. Five of our volunteers attained similar rectal temperatures at exhaustion. Surely, the interesting question (to which we have no answer) is rather why some individual subjects fatigue at 39°C whereas others fatigue at 40°C.
Although our results are consistent with a thermal limitation to performance, their relevance to studies where work rate is not imposed or constant is less clear. The need for regulation of pace by athletes has been recognized since the earliest days of organized competition (e.g., ). Experienced athletics coaches consistently report that errors of pace judgment are most commonly made by inexperienced athletes (2). Morehouse and Miller (7) stated quite specifically that, "the achievement of proper pace requires extensive training," suggesting that this is a learned response rather that a simple feedback system. The history of athletic competition is littered with examples of athletes who spectacularly failed to regulate pace to take account of either the environmental conditions or their physiological capacity. It is indeed the athlete's mind that regulates performance in an anticipatory manner, but the elements of the control loop remain elusive.
Ronald J. Maughan
Susan M. Shirreffs
School of Sport and Exercise Sciences
Jason K. W. Lee
Military Physiology Laboratory
Defence Medical & Environmental Research Institute
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