Key Takeaway
Acute caffeine supplementation (3-6 mg/kg) significantly improves both muscle strength and endurance, with effects modulated by dose and timing.
Summary
This systematic review and meta-analysis examined the acute effects of caffeine capsule ingestion on muscle strength and endurance performance. The researchers analyzed randomized controlled trials comparing caffeine to placebo conditions in healthy adults.
The meta-analysis found significant improvements in both maximal muscle strength (measured via 1RM or isometric tests) and muscle endurance (measured via repetitions to failure). The ergogenic effects were consistent across different muscle groups and exercise modalities.
Subgroup analyses revealed that caffeine doses in the 3-6 mg/kg range produced optimal results, with timing of 30-60 minutes pre-exercise being most effective. The benefits were observed in both trained and untrained individuals, though effect sizes varied based on training status and caffeine habituation.
Methods
- Systematic literature search across PubMed, Web of Science, Scopus, and EBSCO
- Included randomized, double-blind, placebo-controlled trials
- Participants: Healthy adults with no caffeine restrictions
- Intervention: Acute caffeine capsule ingestion (varying doses)
- Outcomes: Muscle strength (1RM, MVC) and muscle endurance (reps to failure)
- Random-effects model for meta-analysis
- Subgroup analyses by dose, timing, muscle group, and training status
Key Results
- Muscle strength: Significant improvement with caffeine vs placebo (SMD = 0.20, p < 0.05)
- Muscle endurance: Significant improvement with caffeine vs placebo (SMD = 0.28, p < 0.01)
- Optimal dose range: 3-6 mg/kg body weight
- Optimal timing: 30-60 minutes pre-exercise
- Effects consistent across upper and lower body exercises
- Low to moderate heterogeneity across studies
Figures
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Limitations
- Most studies used male participants, limiting generalizability to females
- Caffeine habituation status not consistently reported across studies
- Varied definitions of "muscle endurance" across included trials
- Publication bias possible given predominance of positive findings
- Capsule form only - may not generalize to coffee or other caffeine sources