THE EFFECTS OF SUBSTRATE AND FLUID PROVISION ON THERMOREGULATORY, CARDIORESPIRATORY AND METABOLIC RESPONSES TO PROLONGED EXERCISE IN A COLDENVIRONMENT IN MAN

During prolonged exercise in a cold environment, fatigue is generally associated with a depletion of endogenous glycogen stores. This has le ad many authors to hypothesize that the carbohydrate (CHO) content of fluids ingested in cool environments should be high, yet this hypothes is has not been specifically examined. In the present study, six healt hy males cycled to exhaustion at approximately 80 % of their maximum o xygen consumption ((V) over dot(O2,max)) with either no drink (ND), a 15 % CHO-electrolyte drink (15 % CHO) or a 2 % CHO-electrolyte drink ( 2 % CHO). Dietary intake and exercise were replicated 2 days prior to each trial. Mean (S.D.) ambient temperature was 10.0 (0.3) degrees C w ith a relative humidity of 72 (2)% and an air velocity of approximatel y 0.7 m s(-1) on all trials. Weighted mean skin temperature was calcul ated, and rectal temperature and heart rate were recorded at rest, dur ing exercise and at exhaustion. Venous samples were drawn before and d uring exercise and at exhaustion for determination of haemoglobin, hae matocrit, blood metabolites and serum electrolytes and osmolality. Exp ired air was collected for calculation of (V) over dot(O2) and respira tory exchange ratio which were used to estimate rates of fuel oxidatio n. Ratings of perceived exertion (RPE) were also obtained. Exercise ca pacity was not different (P = 0.49) between trials, with median (range ) times to exhaustion of 90.6 (668-106.0), 97.7 (60.9-112.0) and 102.0 (77.1-170.7) min for the ND, 15 % CHO and 2% CHO trials, respectively . The 15 % CHO drink significantly (P < 0.05) elevated blood glucose c oncentration and total CHO oxidation compared with the ND trial. The 2 % CHO drink significantly (P < 0.05) reduced the estimated change in plasma volume and resulted in a lower serum osmolality than the other two trials. No differences were observed in any thermoregulatory or ca rdiorespiratory responses between trials. These data suggest that main tenance of blood-borne substrate and/or plasma volume does not influen ce exercise capacity in the cold, as is commonly reported during this type and intensity of exercise in warmer environments.