Effects of Caffeine on Time Trial Performance and Associated Physiological Responses: A Meta-Analysis

Abstract

Background:

The aim of this study was to conduct a systematic review and meta-analysis on the effects of caffeine supplementation on time trial performance and associated physiological responses.

Methods:

A total of 35 studies met the inclusion criteria of adopting double-blind randomized placebo-controlled crossover designs that included a closed-loop time trial (≥5 minutes) performed under a caffeine dose of 3–6 mg/kg administered 30–90 minutes beforehand. Meta-analyses were completed using a random-effects model, with effects on time trial performance presented as standardized mean difference (δ) and with physiological responses presented as raw mean difference (D). The 95% confidence limits (CL₉₅) were calculated for all estimates.

Results:

Relative to placebo, caffeine had a positive effect on time trial performance (δ = 0.32; CL₉₅ [0.19–0.44]). Moreover, the effect of caffeine on time trial performance corresponded with increases in heart rate (D = 3.3 beats/min; CL₉₅ [1.7–4.8]), oxygen uptake (D = 0.09 L/min; CL₉₅ [0.02–0.17]), blood lactate (D = 1.42 mmol/L; CL₉₅ [1.09–1.74]), and blood glucose (D = 0.94 mmol/L; CL₉₅ [0.58–1.30]). In contrast, caffeine had no effect on time trial measures of respiratory exchange ratio (D = 0.01; CL₉₅ [−0.01 to 0.02]), or ratings of perceived exertion (D = 0.1; CL₉₅ [−0.1 to 0.3]).

Conclusions:

The results reveal a clear effect of caffeine on moderate- to high-intensity time trial performance. When considered in conjunction with research using fixed-intensity exercise, the caffeine-induced increase in time trial intensity likely explains all of the associated increases in heart rate and oxygen uptake, and part of the increase in blood lactate and blood glucose.