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Circadian variation in swim performance.

Christopher E Kline1, J Larry Durstine, J Mark Davis

  • 1Dept. of Exercise Science, Arnold School of Public Health, Univ. of South Carolina, 1300 Wheat St., Columbia, SC 29208, USA.

Journal of Applied Physiology (Bethesda, Md. : 1985)
|November 11, 2006
PubMed
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This study reveals a distinct circadian rhythm in athletic performance, independent of masking factors like sleep and temperature. Swim performance peaks before the lowest body temperature and is worst around waking time.

Area of Science:

  • Sports Science
  • Chronobiology
  • Human Performance

Background:

  • Previous research on time-of-day athletic performance may be influenced by environmental and behavioral masking factors.
  • These factors include sleep patterns, ambient temperature, and energy intake, which can obscure true circadian effects.

Purpose of the Study:

  • To investigate the existence of a circadian rhythm in swim performance.
  • To determine if this rhythm is independent of masking factors.

Main Methods:

  • Twenty-five swimmers participated in a 50-55 hour laboratory study.
  • An ultra-short sleep-wake cycle (1 hour sleep, 2 hours wakefulness) was implemented to equalize masking factors.
  • Six maximal 200-m swim trials were performed by each swimmer at eight different times of day.

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Main Results:

  • A significant circadian rhythm in swim performance was identified (P < 0.001).
  • Performance peaked approximately 5-7 hours before the lowest core body temperature (Tmin).
  • Performance was poorest around the time of Tmin, specifically between 1 hour before and 1 hour after.

Conclusions:

  • A circadian rhythm influences athletic performance, separate from environmental and behavioral masking effects.
  • The findings suggest an internal biological clock significantly impacts physical capabilities.
  • Understanding this rhythm can optimize training and competition schedules for athletes.