Hypohydration and intermittent supramaximal running performance in humans

Reports of hypohydration limiting submaximal exercise performance are well documented (Sawka & Pandolf, 1990). Little is known about the influence of hypohydration on exercise, which is predominantly anaerobic, and previous studies have been conflicting in the results reported (Jacobs, 1980; Nielsen et al. 1981). The purpose of this study, which had ethics committee approval, was to examine the effect of moderate hypohydration on intermittent supramaximal running performance in a cool environment. On two occasions, eleven physically active males performed a maximal anaerobic running test (MART) (Maxwell & Nimmo, 1996) following exercise/heat-induced dehydration. A 2 h rest and rehydration period followed the dehydration on one occasion (euhydrated, EUH) and only a 2 h rest period followed the other (hypohydrated, HYPO). The rehydration fluid was a lemon-flavoured saline solution (80 mmol Fl). The MART protocol involved repeated 20 s runs, each at increasing intensities, with 100 s passive recovery between bouts until exhaustion. In the EUH trial, rehydration during the 2 h rest period resulted in subjects performing the MART with a body weight (mean + S.E.M.) of 0 07 + 0 08 kg (0 1 + 0 1 %) below their initial value. When no fluid was ingested, the body weight deficit prior to the MART was 1P5 + 0 07 kg (2 + 0 07 %). Core temperature and heart rate were measured continuously throughout each trial. A Student's paired t test revealed that performance in the MART was worse in the HYPO (148 + 9 s) compared with the EUH (154 + 9 s) trial (P < 0 05). No differences were found between the EUH and HYPO trial in either peak core temperature (38 0 + 01 vs. 38 1 + 0-1 °C) or maximum heart rate (186 + 2 4 vs.188 + 1P9 beats min-'). In conclusion, these results demonstrate that hypohydration significantly impairs intermittent sprint running performance. REFERENCES Jacobs, I. (1980). It. J Sports M1ed. 1, 21-24. M1axwell, N.S. & Nimmo, M.A. (1996). Cant. J Appl. Physiol. 21, 35-47. Nielsen, B., Kubica, R., Bonnesen, A., Rassmussen, I.B., Stoklosa, J. & Wilk, B. (1981). Scand. J Sports Sci. 3, 2-10. Sawka, M.N. & Pandolf, K.B. (1990). Perspectives in Exercise Science and Sports MJedicine: Fluid Homeostasis During Exercise 3, 1-38.