In-Exercise Caffeine Improves Exercise Performance in the Heat without Exacerbating Hyperventilation and Brain...

Area of Science:

• Exercise Physiology
• Nutritional Science
• Environmental Physiology

Background:

• Pre-exercise caffeine enhances endurance, but heat may negate this effect due to increased physiological strain.
• High caffeine levels in heat can cause hyperthermia, hyperventilation, and cerebral hypoperfusion.
• In-exercise caffeine intake delays blood caffeine elevation, potentially mitigating negative effects in heat.

Purpose of the Study:

• To test if in-exercise caffeine improves performance in prolonged exercise in the heat.
• To assess caffeine's impact on respiratory and cerebral blood flow responses during exercise in heat.
• To evaluate caffeine's effect on body temperature during heat-stress exercise.

Main Methods:

• 12 healthy adults completed cycling tests in 35°C heat.
• Participants consumed caffeine (5 mg/kg) or placebo during moderate-intensity exercise in a crossover design.
• Performance was measured by time to exhaustion during high-intensity cycling.

Main Results:

• In-exercise caffeine intake led to longer high-intensity cycling duration (218 vs. 165 sec).
• Perceived exertion was lower with caffeine during moderate exercise.
• Minute ventilation, cerebral blood flow, and esophageal temperature remained similar between caffeine and placebo trials.

Conclusions:

• In-exercise caffeine intake can improve late-stage exercise performance in the heat.
• This ergogenic effect occurs without worsening hyperthermia, hyperventilation, or cerebral hypoperfusion.
• Timing caffeine intake during exercise is a viable strategy for heat performance.