# Effects of Different Doses of Caffeine on Endurance Exercise Performance in the Heat

## TL;DR

This study found that caffeine improves endurance exercise performance in hot conditions, with higher doses providing greater benefits.

## Contribution

The study demonstrates that 6 mg/kg caffeine dose is more effective than 3 mg/kg in mitigating heat stress effects on endurance performance.

## Key findings

- Caffeine at 6 mg/kg BW prevented heat-induced performance decline unlike 3 mg/kg BW and placebo.
- Higher caffeine doses increased pulmonary ventilation and aerobic capacity during exercise in the heat.
- Only 6 mg/kg BW caffeine significantly reduced perceived fatigue during hot-weather endurance exercise.

## Abstract

This study investigated the effects of different doses of caffeine (3 mg/kg BW and 6 mg/kg BW) on endurance exercise performance in the heat. Seventeen participants completed four randomized, double-blind trials: one in a normal environment (24.6 ± 1.2 °C) and three in a hot environment (33.2 ± 1.4 °C), with placebo, 3 mg/kg BW, and 6 mg/kg BW caffeine interventions. Endurance exercise time, cardiorespiratory function, and subjective fatigue perception were measured during incremental cycling tests. The results showed that high temperatures significantly reduced endurance exercise performance in the placebo (p < 0.001) and 3 mg/kg BW (p = 0.003) groups compared to the normal environment, but not in the 6 mg/kg BW group (p = 1.000). Both caffeine doses improved exercise time compared to placebo (3 mg/kg BW, p = 0.005; 6 mg/kg BW, p < 0.001). Caffeine ingestion enhanced pulmonary ventilation (VE), with significant increases in VEpeak (3 mg/kg BW, p = 0.032; 6 mg/kg BW, p = 0.006). Aerobic capacity improved, as evidenced by elevated VO2peak (3 mg/kg BW, p = 0.010; 6 mg/kg BW, p = 0.001) and PetO2 (3 mg/kg BW, p = 0.000; 6 mg/kg BW, p = 0.001). Subjective fatigue perception was significantly reduced only with 6 mg/kg BW caffeine (p = 0.020). In conclusion, caffeine ingestion at 3 mg/kg BW and 6 mg/kg BW effectively counteracts the negative effects of heat stress on endurance exercise performance by improving respiratory function, enhancing aerobic capacity, and reducing subjective fatigue. The 6 mg/kg BW dose demonstrated superior effects, making it a potential ergogenic aid for athletes training or competing in the heat.