Low-Dose Caffeine May Improve Aerobic Time-Trial Performance
A meta-analysis of placebo-controlled crossover trials found reduced aerobic time-trial completion times with both low- and moderate-dose oral anhydrous caffeine, but the evidence was mostly derived from male participants, cycling studies, and trials using doses no higher than 6 mg/kg.
To evaluate the effects of low-dose oral caffeine supplementation on aerobic time-trial performance in healthy adults.
Approach:
Study Design: Systematic review and meta-analysis of 48 randomized, placebo-controlled crossover trials involving 689 healthy adults aged 18 to 59 years.
Inclusion Criteria: Studies included had to report performance as time-to-completion outcomes and exclude various forms of caffeine administration and non-time-based outcomes.
Caffeine Dosing: Caffeine doses were categorized as low (1.3 to 3 mg/kg), moderate (4 to 6 mg/kg), and high (greater than 6 mg/kg).
Performance Assessment: Performance was primarily evaluated through time-trial tests lasting at least 3 minutes, with most studies focusing on cycling.
Key Findings:
Low-dose caffeine was associated with reduced aerobic time-trial completion time (SMD -0.27).
Moderate-dose caffeine also reduced completion time (SMD -0.52), but the difference in effect size should be interpreted cautiously.
Mean completion-time reductions were approximately 2.14% for low-dose and 2.18% for moderate-dose caffeine.
Sensitivity analyses indicated that differences between low and moderate doses were influenced by specific studies with unique designs or sample characteristics.
Among trained participants, moderate-dose caffeine showed significant performance improvement (SMD -0.81), and even greater in highly trained participants (SMD -0.94).
Interpretation:
The review indicates that low and moderate caffeine doses may enhance aerobic time-trial performance, but findings should be interpreted with caution due to variability in individual responses and study limitations.
Limitations:
Predominantly male sample (642 males vs. 47 females).
High proportion of studies with unclear or high risk of bias.
Insufficient data for robust subgroup analyses by sex or caffeine timing.
No quantification of adverse events related to caffeine use.
Conclusion:
Low and moderate caffeine doses may be effective for improving aerobic time-trial performance, but further research is needed to explore individual sensitivity and the risk-benefit profile of higher doses.
