No effect of caffeine on exercise performance in high ambient temperature

Area of Science:

• Exercise Physiology
• Sports Science
• Human Performance

Background:

• Caffeine is an adenosine receptor antagonist known to enhance performance at normal temperatures.
• Limited research exists on caffeine's effects on exercise performance and thermoregulation in hot environments.
• Understanding caffeine's impact in heat is crucial for athletes and sports science.

Purpose of the Study:

• To investigate the effects of caffeine on exercise performance and thermoregulation in high ambient temperature (30°C).
• To determine if caffeine provides an ergogenic effect during prolonged cycling followed by a time trial in the heat.

Main Methods:

• Eight healthy trained male cyclists participated in a double-blind, randomized crossover trial.
• Subjects ingested either placebo or caffeine (6 mg/kg) one hour before cycling at 55% W (max) for 60 minutes, followed by a performance time trial.
• Measurements included performance metrics, rectal temperature, and plasma beta-endorphin concentrations.

Main Results:

• Caffeine administration did not significantly alter exercise performance (p = 0.462).
• Rectal temperature was significantly elevated following caffeine ingestion (p < 0.036).
• Plasma beta-endorphin concentrations were significantly increased at the end of the time trial with caffeine (p = 0.032).

Conclusions:

• Caffeine does not appear to offer ergogenic benefits for exercise performance when ingested one hour before exercise in 30°C heat.
• The observed increase in core body temperature with caffeine may counteract potential performance-enhancing effects in hot conditions.
• Interindividual variability and altered neurotransmitter concentrations could also influence caffeine's efficacy in heat.