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Hypothalamic-pituitary-adrenal responses to short-duration high-intensity cycle exercise
W J Kraemer1, J F Patton, H G Knuttgen
1Exercise Physiology Division, US Army Research Institute of Environmental Medicine, Natick 01760-5007.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|January 1, 1989
Summary
High-intensity exercise significantly impacts beta-endorphin (beta-EP) and adrenocorticotropin (ACTH) levels, with cortisol also increasing at 36% maximal leg power. These hormonal responses to exercise are nonlinear and not directly related to blood lactate at high intensities.
Area of Science:
- Exercise Physiology
- Endocrinology
- Sports Science
Background:
- Hormonal responses to exercise, including beta-endorphin (beta-EP), adrenocorticotropin (ACTH), and cortisol, are critical for understanding physiological adaptation.
- Previous research suggests exercise intensity influences these hormonal changes, but the precise patterns, especially at maximal efforts, require further elucidation.
Purpose of the Study:
- To investigate the acute effects of varying maximal exercise intensities on plasma concentrations of beta-EP, ACTH, and cortisol.
- To examine the relationship between these hormones, blood lactate levels, and specific physiological markers like capillary density and muscle fiber type.
Main Methods:
- Subjects underwent maximal exercise testing on a cycle ergometer at four intensities: 36%, 55%, 73%, and 100% of maximal leg power (MLP).
- Blood samples were collected at rest, immediately post-exercise, and at 5 and 15 minutes post-exercise for hormonal and lactate analysis.
- Correlations were assessed between hormone levels and capillary density or type II muscle fiber percentage.
Main Results:
- Significant increases in beta-EP and ACTH were observed at 36% MLP immediately and up to 15 minutes post-exercise.
- Plasma cortisol levels increased at 36% MLP at 15 minutes post-exercise.
- Blood lactate significantly increased across various intensities, but showed no clear relationship with hypothalamic-pituitary-adrenal hormones at high exercise intensities.
Conclusions:
- Brief, high-intensity exercise elicits a nonlinear response pattern in peripheral blood hormone concentrations.
- Hormonal responses, particularly beta-EP and ACTH, are sensitive to exercise intensity even below maximal levels.
- Blood lactate accumulation does not appear to correlate with hypothalamic-pituitary-adrenal hormone levels during maximal exercise efforts.