Forskning

July 26, 2018

Increased rate of heat storage, and no performance benefits, with caffeine ingestion before a 10-km run in hot, humid conditions

N J Hanson et al, 2018. Increased rate of heat storage, and no performance benefits, with caffeine ingestion before a 10-km run in hot, humid conditions, Int J Sports Physiol Perform, published online.

ABSTRACT:

Purpose: Although the effect of caffeine in thermoneutral or cool environmental conditions has generally shown performance benefits, its efficacy in hot, humid conditions is not as well known. The purpose of this study was to further examine the effect of caffeine ingestion on endurance running performance in the heat.

Methods: Ten trained endurance runners (6 males; mean ±SD age 26±9 years, height 176.7±5.1 cm, mass 72.1±8.7 kg) came to the lab for four visits. The first was a VO₂max test to determine cardiorespiratory fitness; the final three visits were 10km runs in an environmental chamber at 30.6°C and 50% RH under different conditions: 3 mg·kg^-1 body mass (low caffeine dosage), 6 mg·kg^-1 (moderate dosage), and a placebo. Repeated-measures ANOVAs were used to determine the effect of condition on 10km time, heart rate (HR), core temperature (C_T), rating of perceived exertion (RPE) and thermal sensation (TS).

Results: There was no difference in 10km time between the placebo (53.2±8.0 min.), 3 mg·kg^-1 (53.4±8.4) and 6 mg·kg^-1 (52.7±8.2) conditions (p=.575, η_p²=.060). There was not a main effect of average HR (p=.406, η_p²=.107), RPE (p=.151, η_p²=.189) or TS (p=.286, η_p²=.130). There was a significant interaction for CT (p=.025, η_p²=.170); the moderate dosage caffeine condition showed a higher rate of rise in CT (0.26±0.08 ˚C·km^-1 vs. 0.20±0.06 and 0.19±0.10 in the low caffeine and placebo conditions, respectively).

Conclusion: The results support previous research showing a thermogenic effect of caffeine, as the moderate dosage condition led to a greater rate of heat storage and no performance benefits.