Acute Effects of Caffeine and Taurine Co‐Ingestion on Time to Exhaustion and Thermoregulatory Responses to Cycling in the Heat

Caffeine and taurine are commonly co-ingested pre-exercise but elicit different thermoregulatory responses; however, their combined effect on thermoregulation is unknown. Therefore, we evaluated the effects of oral caffeine and taurine co-ingestion on time to exhaustion (TTE) and thermoregulatory responses to cycling in the heat at the gas exchange threshold (GET). Ten healthy nonheat acclimated participants took part in a double-blind crossover study, completing a TTE in the heat (35°C; 40% relative humidity), cycling at a power output associated with the GET and 1 h after ingesting: caffeine (5 mg/kg) and taurine (50 mg/kg) combined or placebo. Pulmonary gas exchange, core and mean skin temperatures and whole-body sweat rate (WBSR) were recorded throughout. Heat production was determined using partitional calorimetry. There were no differences in TTE between conditions (p = 0.608); however, the rate of oxygen consumption (p = 0.017), minute ventilation (p = 0.029) and heat production (p = 0.019) were higher following the supplement. There were no differences between conditions for skin (p = 0.539) and core temperature (p = 0.699), mean skin blood flow (p = 0.119), respiratory exchange ratio (p = 0.546) and WBSR (p = 0.897). Pre-exercise co-ingestion of caffeine and taurine in the heat had no ergogenic effect despite increasing the ventilatory and metabolic demand. Collectively, these data indicate minimal effects on whole-body thermoregulation.