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Twenty minutes of voluntary hypocapnic hyperventilation prior to exercise reduces the aerobic metabolic rate with a compensatory increase in the anaerobic metabolic rate without affecting exercise performance during the Wingate anaerobic test (WAnT). Thus, pre-exercise hypocapnic hyperventilation may be a useful means of stressing the anaerobic energy system during training, ultimately improving anaerobic exercise performance. However, it remains unclear whether a shorter (e.g., 5 min) pre-exercise hypocapnic hyperventilation is sufficient to reduce the aerobic metabolic rate during high-intensity exercise. We therefore compared the effects of 5-min and 20-min pre-exercise hypocapnic hyperventilation on aerobic metabolism during the 30-s WAnT. Ten healthy young males and one female performed the WAnT following 20 min of spontaneous breathing (control trial) or 5 or 20 min of voluntary hypocapnic hyperventilation. Both the 5-min and 20-min hyperventilation reduced end-tidal CO2 partial pressure (an index of arterial CO2 partial pressure) to ∼23 mmHg, whereas it remained unchanged during the spontaneous breathing. The peak, mean and minimum power outputs during the WAnT did not differ among the three trials. Oxygen uptake during the WAnT was lower in both the 5-min (1493 ± 257 mL min−1) and 20-min (1397 ± 447 mL min−1) hyperventilation trials than during the control trial (1847 ± 286 mL min−1), and was similar in the two hyperventilation trials. These results suggest that 5 min of pre-exercise hypocapnic hyperventilation reduces aerobic metabolism during the 30-s WAnT to a level similar to that seen with the 20-min hyperventilation. Moreover, exercise performance was unaffected, which implies anaerobic metabolism was enhanced. [ABSTRACT FROM AUTHOR]

Introduction: Caffeine is an exercise performance enhancer widely used by individuals engaged in training or competition under heat-stressed conditions. Caffeine ingestion during exercise in the heat is believed to be safe because it does not greatly affect body temperature responses, heart rate, or body fluid status. However, it remains unknown whether caffeine affects hyperthermia-induced hyperventilation or reductions in the cerebral blood flow index. We tested the hypothesis that under conditions inducing severe hyperthermia, caffeine exacerbates hyperthermia-induced hyperventilation and reduces the cerebral blood flow index during exercise. Methods: Using a randomized, single-blind, crossover design, 12 physically active healthy young men (23 ± 2 yr) consumed a moderate dose of caffeine (5 mg·kg−1) or placebo in the heat (37°C). Approximately 60 min after the ingestion, they cycled for ~45 min at a workload equal to ~55% of their predetermined peak oxygen uptake (moderate intensity) until their core temperature increased to 2.0°C above its preexercise baseline level. Results: In both trials, ventilation increased and the cerebral blood flow index assessed by middle cerebral artery mean blood velocity decreased as core temperature rose during exercise (P < 0.05), indicating that hyperthermia-induced hyperventilation and lowering of the cerebral blood flow occurred. When core temperature was elevated by 1.5°C or more (P < 0.05), ventilation was higher and the cerebral blood flow was lower throughout the caffeine trial than the placebo trial (P < 0.05). Conclusions: A moderate dose of caffeine exacerbates hyperthermia-induced hyperventilation and reductions in the cerebral blood flow index during exercise in the heat with severe hyperthermia. [ABSTRACT FROM AUTHOR]