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Sleep in endurance sports – Part 2: Circadian rhythm & sleep types

Today we explain what the circadian rhythm is and why the bird names lark and owl are related to sleep types. More information can be found on our blog! If you have any questions, write to us and we will answer them in our next podcast mini-series.

Circadian rhythm (sleep-wake rhythm)

The ability of an organism to synchronize physiological processes to a period of about 24 hours.

  • Largely independent of external factors
  • Gives a time frame to the various functions of the whole organism

Physiology

  • Photoreceptors in the outer granular layer of the retina (within the eye) perceive the light
  • The photosensitive ganglion cells of the eye produce the protein melanopsin 
  • This directs the perception of light to the nucleus suprachiasmaticus (NSC)

Nucleus suprachiasmaticus

  • Acts as a coordinator of cellular functions such as:
    • Body temperature
    • Melatonin distribution (“sleep hormone”)
    • Blood pressure fluctuations
    • Heart rate

Disturbances in the sleep-wake rhythm:

  • Reduced daylight 
  • Exposure to artificial light at night (shift work/laptops/mobile phones/..)
  • Travelling over time zones

Sleep Types

  • Extreme forms of the circadian rhythms are the morning type (“lark”) and the evening type (“owl”)

Lark

  • Performance peak in the early morning 
  • Sleep-wake rhythm is shifted forward
  • Sleep phases range from about 8pm to 5am

Owl

  • Performance peak late in the evening
  • Sleep-wake rhythm is delayed
  • Sleep phases range from about 2am to 11am

Checklist for a good sleep

  1. Quiet environment, dark room
  2. Room temperature approx. 18 degrees 
  3. Sleep routine: Similar bedtime and wake-up times 
  4. Avoid the use of mobile phones, computers and TV for about 1 hour before going to bed

Quellen

  1. Halson, S. L. (2014). Sleep in Elite Athletes and Nutritional Interventions to Enhance Sleep. Sports Medizin. 
  2. Hamet P., Tremblay J. (2006) Genetics of the sleep-wake cycle and its disorders. Metabolism Clinical and Experimental 55 (Suppl 2), 7-12.
  3. Okamura H. (2003) Circadian and Seasonal Rhythms – Integration of mammalian circadian clock signals: from molecule to behavior. Journal of Endocrinology 177, 3-6.
  4. Taheri S., Mignot E. (2002) The genetics of sleep disorders – Review. The Lancet Neurology Vol 1, 242-250.
  5. Merck, et al., Zirkadiane Rhythmusstörungen mit Schlafstörungen. Zugriff am 08.06.2020 unter: https://www.msdmanuals.com/de-de/profi/neurologische-krankheiten/schlafstörungen-und-störungen-des-schlaf-wach-rhythmus/zirkadiane-rhythmusstörungen-mit-schlafstörungen.
  6. Marshall, G. J., & Turner, A. N. (2016). The importance of sleep for athletic performance. Strength & Conditioning Journal, 38(1), 61-67.