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Evening high-intensity swimming exercise impairs REM sleep and increases wake after sleep onset in male swimmers

In a crossover trial, 12 competitive male swimmers completed high-intensity evening swimming (6:30-8:30 pm) and a no-exercise control condition. The exercise condition significantly reduced REM sleep duration (81.4 vs 107.6 min) and increased wake after sleep onset (23.5 vs 3.4 min) compared to control, while other sleep variables were unaffected. Core body temperature was higher during exercise but returned to baseline by bedtime.

Last updated: Aug 17, 2026•1 RCTs•📖 Read as article →

Evidence Score

Evidence Score42/100
Human RCT★★☆☆☆
Meta-analysis☆☆☆☆☆
Mechanism★★★★★
Safety★★★★☆
Confidencelow

Study Evidence

Study 1. The effect of evening swimming exercise on sleep parameters in male swimmers.

observational

Furukawa H, Natsui T, Chugun T, Tomiishi C, Mizuno R, Maeoka Y, Goto K · Physiological reports (2026)

Participants: N/A
Duration: Crossover design, two trials (exercise and control) on separate days
Intervention: High-intensity evening swimming exercise from 6:30-8:30 pm
Outcome: Sleep parameters measured via EEG (REM duration, wake after sleep onset, other sleep stages), core body temperature
Effect Size: N/A
Population: 12 competitive male swimmers

Result:

PubMed: 42590815DOI: 10.14814/phy2.71050

Mechanism Graph

Evening high-intensity exercise elevates core body temperature during exercise
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Core body temperature returns to baseline by bedtime
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Despite normal bedtime temperature, REM sleep is reduced and wake after sleep onset is increased
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Result: Selective impairment of REM sleep and sleep maintenance

Limitations

  • ⚠Small sample size (n=12) limits generalizability
  • ⚠Only male swimmers studied, not applicable to females or non-athletes
  • ⚠Crossover design but no washout period mentioned
  • ⚠No subjective sleep quality measures reported

Frequently Asked Questions

Does evening swimming exercise affect total sleep time?▼

No, the study found no significant difference in total sleep time between exercise and control conditions; only REM sleep duration and wake after sleep onset were affected.

Why does evening exercise impair sleep if body temperature is normal at bedtime?▼

The study suggests that the elevated core body temperature during exercise may have a delayed effect on sleep architecture, even though temperature normalizes by bedtime. The exact mechanism is not fully understood.

Is this effect specific to swimming or would other evening exercise have similar effects?▼

This study only tested swimming, so it cannot be generalized to other forms of exercise. However, the findings suggest that high-intensity evening exercise may have selective effects on sleep.

What are the practical implications for athletes?▼

Competitive swimmers who train in the evening may experience reduced REM sleep and more fragmented sleep, which could affect recovery and performance. Athletes might consider adjusting training times or sleep hygiene strategies.

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References

  1. 1.Furukawa H, Natsui T, Chugun T, Tomiishi C, Mizuno R, Maeoka Y, Goto K. "The effect of evening swimming exercise on sleep parameters in male swimmers.." Physiological reports, 2026. PMID: 42590815 DOI: 10.14814/phy2.71050
Disclaimer: This content is for educational purposes only and is not medical advice. Evidence scores reflect the quality and quantity of available research, not clinical recommendations. Always consult a healthcare professional before starting any supplement or intervention.