title: Exercise and circulating cortisol levels: the intensity threshold effect.
abstract: This study examined the influence of exercise intensity upon the cortisol response of the hypothalamic-pituitary-adrenal (HPA) axis. Specifically, we examined exercise at intensities of 40, 60, and 80% maximal oxygen uptake (VO2max) in an attempt to determine the intensity necessary to provoke an increase in circulating cortisol. Twelve active moderately trained men performed 30 min of exercise at intensities of 40, 60, and 80% of their VO2max, as well as a 30-min resting-control session involving no exercise on separate days. Confounding factors such as time of day--circadian rhythms, prior diet--activity patterns, psychological stress, and levels of exercise training were controlled. Cortisol and ACTH were assessed in blood collected immediately before (pre-) and after (post-) each experimental session. Statistical analysis involved repeated measures analysis of variance and Tukey post-hoc testing. The percent change in cortisol from pre- to post-sampling at each session was: resting-control, 40, 60, and 80% sessions (mean+/-SD) =-6.6+/-3.5%, +5.7+/-11.0%, +39.9+/-11.8%, and +83.1+/-18.5%, respectively. The 60% and 80% intensity magnitude of change was significantly greater than in the other sessions, as well as from one to another. The ACTH responses mirrored those of cortisol, but only the 80% exercise provoked a significant (p<0.05) increase pre- to post-exercise. The calculated changes in plasma volume for the resting-control, 40%, 60%, and 80% sessions were: +2.2+/-3.0%, -9.9+/-5.0%, -15.6+/-3.5%, and -17.2+/-3.3%, respectively. Collectively, the cortisol findings support the view that moderate to high intensity exercise provokes increases in circulating cortisol levels. These increases seem due to a combination of hemoconcentration and HPA axis stimulus (ACTH). In contrast, low intensity exercise (40%) does not result in significant increases in cortisol levels, but, once corrections for plasma volume reduction occurred and circadian factors were examined, low intensity exercise actually resulted in a reduction in circulating cortisol levels.
authors.affiliation: Endocrine Section, Applied Physiology Laboratory, Department of Exercise & Sport Science, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
authors.forename: E E
authors.initials: EE
authors.lastname: Hill
authors.forename: E
authors.initials: E
authors.lastname: Zack
authors.forename: C
authors.initials: C
authors.lastname: Battaglini
authors.forename: M
authors.initials: M
authors.lastname: Viru
authors.forename: A
authors.initials: A
authors.lastname: Viru
authors.forename: A C
authors.initials: AC
authors.lastname: Hackney
mesh_terms: D000293:Adolescent; D000324:Adrenocorticotropic Hormone / Q000097:blood; D000328:Adult; D000893:Anti-Inflammatory Agents / Q000097:blood*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology; D008297:Male; D010807:Physical Endurance / Q000502:physiology*; D010913:Pituitary-Adrenal System / Q000502:physiology; D011897:Random Allocation; D011795:Surveys and Questionnaires; D055815:Young Adult
chemical_list: D000893:Anti-Inflammatory Agents; D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone
references.citation: J Appl Physiol (1985). 1995 May;78(5):1657-64
references.pmid: 7649899
references.citation: J Appl Physiol. 1973 Dec;35(6):887-91
references.pmid: 4765828
references.citation: Expert Rev Endocrinol Metab. 2006 Nov 1;1(6):783-792
references.pmid: 20948580
references.citation: J Sports Sci. 2001 Nov;19(11):893-8
references.pmid: 11695511
references.citation: J Physiol. 1976 Jun;258(1):1-18
references.pmid: 940045
references.citation: J Appl Physiol. 1974 Aug;37(2):247-8
references.pmid: 4850854
references.citation: Med Sci Sports Exerc. 1996 Aug;28(8):1015-9
references.pmid: 8871911
references.citation: Int J Sports Med. 1992 Apr;13(3):201-9
references.pmid: 1601554
references.citation: N Engl J Med. 1987 May 21;316(21):1309-15
references.pmid: 3033504
references.citation: J Sports Sci. 1998 Feb;16(2):121-8
references.pmid: 9531001
references.citation: Eur J Appl Physiol. 2001 Oct;85(6):578-85
references.pmid: 11718288
references.citation: Horm Metab Res. 1992 Apr;24(4):147-53
references.pmid: 1601387
references.citation: J Strength Cond Res. 2002 May;16(2):286-9
references.pmid: 11991783
references.citation: Eur J Appl Physiol Occup Physiol. 1997;75(4):343-50
references.pmid: 9134366
references.citation: Int J Sports Med. 2004 Aug;25(6):461-4
references.pmid: 15346236