title: Thyroid hormonal responses to intensive interval versus steady-state endurance exercise sessions.
abstract: OBJECTIVE
  To compare the thyroid hormonal responses to high-intensity interval exercise (IE) and steady-state endurance exercise (SEE) in highly trained males (n=15).
  
  
  METHODS
  The IE session consisted of repeated periods of 90-seconds treadmill running at 100-110% VO(2max) and 90-seconds active recovery at 40% VO(2max) for 42-47 minutes. The SEE session was a 45-minute run at 60-65% VO(2max). Total work output was equal for each session. A 45-minute supine rest control session (CON) was also performed. Pre-session (PRE), immediate post-session (POST), and 12-hours post-session (12POST) blood samples were collected and used to determine free (f) T₄, fT₃, reverse (r) T₃, and cortisol levels.
  
  
  RESULTS
  All PRE hormone levels were within clinical norms and did not differ significantly between sessions. All POST IE and SEE hormone levels were significantly elevated compared to POST CON (p<0.001). At 12POST, no significant differences between CON and SEE hormonal levels were observed; however, fT₃ was significantly reduced and rT3 was significantly elevated in 12POST IE compared to 12POST SEE and CON (p=0.022). For IE, at 12POST a negative correlation (r(s) = -0.70, p<0.004) was found between fT₃ and rT₃.Also, for IE, a positive correlation (r(s) = 0.74, p<0.002) between cortisol POST and rT₃ 12POST was noted, and a negative correlation (r(s) = -0.72, p<0.003) between cortisol POST and fT₃ 12POST.
  
  
  CONCLUSIONS
  IE results in a suppressed peripheral conversion of T₄ to T₃ implying that a longer recovery period is necessary for hormonal levels to return to normal following IE compared to SEE. These findings are useful in the implementation of training regimens relative to recovery needs and prevention of over-reaching-overtraining.
authors.affiliation: Endocrine Section-Applied Physiology Laboratory, Department of Exercise & Sport Science, University of North Carolina, Chapel Hill, North Carolina, USA. ach@email.unc.edu
authors.forename: Anthony C
authors.initials: AC
authors.lastname: Hackney
authors.forename: Ashley
authors.initials: A
authors.lastname: Kallman
authors.forename: Karen P
authors.initials: KP
authors.lastname: Hosick
authors.forename: Daniela A
authors.initials: DA
authors.lastname: Rubin
authors.forename: Claudio L
authors.initials: CL
authors.lastname: Battaglini
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D013974:Thyroxine / Q000097:blood / Q000378:metabolism*; D013997:Time Factors; D014284:Triiodothyronine / Q000097:blood / Q000378:metabolism*
chemical_list: D014284:Triiodothyronine; D013974:Thyroxine