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The purpose of this study was to determine if intravenous fluid rehydration, versus oral rehydration. during a brief period (20 min) differentially affects plasma ACTH, cortisol, and norepinephrine concentrations during subsequent exhaustive exercise in the heat. Following dehydration (DHY) to −4% of body weight, 8 nonacclimated highly trained males (age = 23.5 ± 1.2 years, V̇O_2peak = 61.4±0.8 ml · kg · min⁻¹, % body fat = 13.5±0.6%) cycled to exhaustion at 74% V̇O_2peak in 36.8 °C on three different occasions. These included: (a) no fluid (NF), where no fluid was provided during the rehydration period; (b) DRINK, where oral rehydration (0.45% NaCl) was provided equal to 50% of the prior DHY; and (c) IV, where intravenous infusion (0.45% NaCl) was provided equal to 50%’ of the prior DHY. Exercise time to exhaustion was not different p = .07) between the DRINK (34.86 ±4.01) and IV (29.48 ± 3.50) trials, but both were significantly p < .05) longer than the NF (18.95 ± 2.73) trial. No differences (p > .05) were found for any of the hormone measures among trials. The endocrine responses at exhaustion were similar regardless of hydration state and mode of rehydration, but rehydration prolonged the exercise time to exhaustion.

The aim of the present study was to investigate the effect of vitamin C with or without carbohydrate consumed acutely in beverages before and during prolonged cycling on immunoendocrine responses. In a single blind, randomized manner six healthy, moderately trained males exercised for 2.5 h at 60% VO_2max and consumed either placebo (PLA), carbohydrate (CHO, 6% w/v), vitamin C (VC, 0.15% w/v) or CHO+VC beverages before and during the bouts; trials were separated by 1 wk. CHO and CHO+VC significantly blunted the post-exercise increase in plasma concentrations of cortisol, ACTH, total leukocyte, and neutrophil counts and limited the decrease in plasma glucose concentration and bacteria-stimulated neutrophil degranulation. VC increased plasma antioxidant capacity (PAC) during exercise (P < 0.05) but had no effect on any of the immunoendocrine responses (P > 0.05). CHO+VC increased PAC compared to CHO but had no greater effects, above those observed with CHO alone, on any of the immunoendocrine responses. In conclusion, acute supplementation with a high dose of VC has little or no effect on the hormonal, interleukin-6, or immune response to prolonged exercise and combined ingestion of VC with CHO provides no additional effects compared with CHO alone.

The effects of ingesting a low dose of CHO on plasma glucose, glucoregulatory hormone responses, and performance during prolonged cycling were investigated. Nine male subjects cycled for 165 min at ≈67% peak ${\text{VO}}_2$ followed by a two-stage performance ride to exhaustion on two occasions in the laboratory. Every 20 min during exercise, subjects consumed either a flavored water placebo (P) or a dilute carbohydrate beverage (C). Blood samples were collected immediately before, every 20 min throughout, and immediately after exercise. Plasma was analyzed for glucose, lactate, free fatty acids (FFA), and various glucoregulatory hormones. ${\text{VO}}_2$ , RER, heart rate, perceived exertion, and exercise performance were also measured. Lactate, FFA, epinephrine, norepinephrine, ACTH, cortisol, and glucagon increased with exercise whereas glucose and insulin decreased (p≤05). Except for a small difference in glucose at 158 min of exercise and at exhaustion, no significant differences were found between drinks for any of the variabfes studied (p ≥ 05). Ingestion of 13 g carbohydrate per hour is not sufficient to maintain plasma glucose, attenuate the glucoregulatory hormone response, and improve performance during prolonged moderate intensity cycling.