title: An out-of-lab trial: a case example for the effect of intensive exercise on rhythms of human clock gene expression.
abstract: BACKGROUND
  Although out-of-lab investigation of the human circadian clock at the clock gene expression level remains difficult, a recent method using hair follicle cells might be useful. While exercise may function as an entrainment cue for circadian rhythms, it remains unclear whether exercise affects human circadian clock gene expression.
  
  
  METHODS
  Efforts to observe apparent effects of exercise on clock gene expression require that several specific conditions be met: intense exercise should be habitually performed at a relatively uncommon time of day over an extended period; and any relative phase shift thereby observed should be validated by comparison of exercise and no-exercise periods. Wake-up and meal times should be kept almost constant over the experimental period. The present study was conducted using a professional fighter who met these strict criteria as subject. Facial hair samples were collected at 4-h intervals around the clock to ascertain rhythms of clock gene expression.
  
  
  RESULTS
  During a period in which nighttime training (from 20:00 to 22:00) was habitually performed, circadian clock gene expression was phase-delayed by 2 to 4 h compared with that during a no-exercise period. Maximum level and circadian amplitude of clock gene expression were not affected by the nighttime training.
  
  
  CONCLUSIONS
  Our trial observations illustrate the possibility that heavy physical exercise might strongly affect the circadian phase of clock gene expression. Exercise might be therefore effective for the clinical care of circadian disorders. The results also suggest that athletes may require careful scheduling of heavy physical exercise to maintain normal circadian phase and ensure optimal athletic performance.
authors.affiliation: The Research Institute for Time Studies, Yamaguchi University, 1677-1 Yoshida, Yamaguchi 753-8511, Japan. akashima@yamaguchi-u.ac.jp.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Okamoto
authors.forename: Takuro
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Matsumura
authors.forename: Koichi
authors.initials: K
authors.lastname: Node
authors.forename: Makoto
authors.initials: M
authors.lastname: Akashi