Objective:

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.

Sources:

• Nutrients