title: Exercise intensity and its effects on thyroid hormones.
abstract: BACKGROUND
  Physical activity influences energy metabolism in human subjects by increasing activity-induced energy expenditure and resting metabolic rate for several hours after exercise. Effects of exercise on circulating thyroid hormone values remain controversial. We have investigated the effect of acute aerobic exercise on thyroid hormone values.
  
  
  METHODS
  The effect of different intensity levels of acute aerobic exercise on thyroid hormones was investigated in 60 male well-trained athletes by performing bicycle ergometer at 45% (low intensity), 70% (moderate intensity), and 90% (high intensity). These intensities were selected according to their maximum heart rate (MHR). At each intensity level, heart rate, blood lactic acid, serum total thyroxine (T4), free thyroxine (fT4), total triiodothyronine (T3), free triiodothyronine (fT3) and thyroid stimulating hormone (TSH) values were measured.
  
  
  RESULTS
  The results of this study show that exercise performed at the anaerobic threshold (70% of maximum heart rate, lactate level 4.59 +/- 1.75 mmol/l) caused the most prominent changes in the amount of any hormone values. While the rate of T4, fT4, and TSH continued to rise at 90% of maximum heart rate, the rate of T3 and fT3 started to fall.
  
  
  CONCLUSIONS
  Maximal aerobic exercise greatly affects the level of circulating thyroid hormones.
authors.affiliation: GENLAB Medical Diagnostics and Research Laboratory, Istanbul, Turkey.
authors.forename: Figen
authors.initials: F
authors.lastname: Ciloglu
authors.forename: Ismail
authors.initials: I
authors.lastname: Peker
authors.forename: Aysel
authors.initials: A
authors.lastname: Pehlivan
authors.forename: Kursat
authors.initials: K
authors.lastname: Karacabey
authors.forename: Nevin
authors.initials: N
authors.lastname: Ilhan
authors.forename: Ozcan
authors.initials: O
authors.lastname: Saygin
authors.forename: Recep
authors.initials: R
authors.lastname: Ozmerdivenli
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004734:Energy Metabolism / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D005082:Physical Exertion; D012016:Reference Values; D018709:Statistics, Nonparametric; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*
chemical_list: D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine