Caffeine is one of the most widely used performance aids in sport. But when taken in the evening, its benefits may come with a price. A recent controlled study explored how different doses of caffeine consumed in the evening affect rowing performance, sleep quality, and next-day alertness in trained athletes.
The results highlight a clear dose–response trade-off between performance and recovery.
Study Overview
Participants
- 13 trained male university rowers
- Average age: 22 years
- Average body mass: ~78 kg
Design
- Double-blind, randomized, crossover
- Four separate evening trials (19:00–20:00)
Performance test
- Standard 2,000 m rowing ergometer time trial (Concept II)
Recovery markers
- Sleep quality (self-reported the following morning)
- Daytime sleepiness (Karolinska Sleepiness Scale)
- Adverse effects (headache, insomnia, GI discomfort)
Performance Results
Caffeine clearly improved rowing performance, but only at moderate to high doses.
- 6 mg/kg and 9 mg/kg significantly improved:
- 2,000 m completion time
- Average power output
- The highest dose (9 mg/kg) produced the largest performance gains
- Small-to-moderate effect sizes (d ≈ 0.40–0.41)
- 3 mg/kg showed only mild improvements, often not clearly different from placebo
Takeaway:
Higher doses led to faster times and more power, but the gains were incremental rather than dramatic.
Sleep and Wakefulness Outcomes
This is where the trade-off became obvious.
Sleep Quality
- Moderate (6 mg/kg) and high (9 mg/kg) doses significantly reduced perceived sleep quality
- Effect sizes were large (d ≈ 1.3–1.5)
Daytime Sleepiness
- Athletes reported higher next-day sleepiness after moderate and high doses
- This suggests incomplete recovery despite improved performance the night before
Side Effects
- Mostly reported in the high-dose condition (9 mg/kg):
- Headaches
- Insomnia
- Gastrointestinal discomfort
Low-dose caffeine caused minimal sleep disruption and few side effects.
The Dose–Response Reality
The study demonstrates a clear pattern:
- More caffeine = better evening performance
- More caffeine = worse sleep and recovery
Only the highest dose produced notable performance benefits, but it also caused the largest physiological and perceptual costs.
This matters because sleep quality is directly linked to:
- Glycogen restoration
- Hormonal balance
- Neuromuscular recovery
- Next-day training quality
In endurance sports, short-term gains can easily undermine long-term adaptation.
Practical Takeaways for Athletes and Coaches
If training or racing in the evening:
- Use low doses (≈3 mg/kg) if caffeine is needed
- Expect modest performance effects with minimal recovery disruption
If maximal performance is the priority (e.g. finals, one-off races):
- Moderate doses may help, but plan for reduced sleep quality
- Avoid repeated use on consecutive days
Avoid high doses (≈9 mg/kg) unless absolutely necessary
- Performance gains are real, but recovery costs are substantial
- Side effects become much more likely
Bottom Line
Evening caffeine works, but it is not free.
Higher doses can improve rowing performance, yet they significantly impair sleep quality and increase next-day sleepiness. Over time, this trade-off may limit consistency, recovery, and long-term progress.
Performance is not just about going harder today, but recovering well enough to repeat it tomorrow.
In endurance sport, caffeine should be strategic, not habitual.