Physiological responses to short-term exercise in the heat after creatine loading

Purpose: This investigation was designed to examine the influence of creati ne (Cr) supplementation on acute cardiovascular, renal, temperature, and fl uid-regulatory hormonal responses to exercise for 35 min in the heat. Metho ds: Twenty healthy men were matched and then randomly assigned to consume 0 .3 g . kg(-1) Cr monohydrate (N = 10) or placebo (N = 10) for 7 d in a doub le-blind fashion. Before and after supplementation, both groups cycled for 30 min at 60-70% VO2peak immediately followed by three 10-s sprints in an e nvironmental chamber at 37 degreesC and 80% relative humidity. Results: Bod y mass was significantly increased (0.75 kg) in Cr subjects. Heart rate, bl ood pressure, and sweat rate responses to exercise were not significantly d ifferent between groups. There were no differences in rectal temperature re sponses in either group. Sodium, potassium, and creatinine excretion rates obtained from 24-h and exercise urine collection periods were not significa ntly altered in either group. Serum creatinine was elevated in the Cr group but within normal ranges. There were significant exercise-induced increase s in cortisol, aldosterone, renin, angiotensin I and II, atrial peptide, an d arginine vasopressin. The aldosterone response was slightly greater in th e Cr (263%) compared with placebo (224%) group. Peak power was greater in t he Cr group during all three 10-s sprints after supplementation and unchang ed in the placebo group. There were no reports of adverse symptoms, includi ng muscle cramping during supplementation or exercise. Conclusion: Cr suppl ementation augments repeated sprint cycle performance in the heat without a ltering thermoregulatory responses.