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Related Experiment Video

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Conducting Maximal and Submaximal Endurance Exercise Testing to Measure Physiological and Biological Responses to Acute Exercise in Humans
07:26

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Published on: October 17, 2018

Hormonal responses during a prolonged military field exercise with variable exercise intensity.

Heikki Kyröläinen1, Jari Karinkanta, Matti Santtila

  • 1Department of Biology of Physical Activity, University of Jyväskylä, 40114, Jyväskylä, Finland. heikki.kyrolainen@sport.jyu.fi

European Journal of Applied Physiology
|November 28, 2007
PubMed
Summary

Prolonged military exercise alters hormones. Lower energy deficits (ED) during exercise allowed hormonal recovery, while high ED initially caused significant changes in cortisol, growth hormone, and testosterone levels.

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Last Updated: Jul 9, 2026

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Area of Science:

  • Exercise Physiology
  • Endocrinology
  • Sports Science

Background:

  • Military field exercises involve prolonged physical exertion and can induce significant energy deficits.
  • Hormonal responses to exercise are complex and influenced by factors like energy availability and deficit.
  • Understanding these hormonal shifts is crucial for maintaining soldier health and performance.

Purpose of the Study:

  • To investigate how varying energy deficits (ED) during a prolonged military field exercise affect hormonal concentration changes.
  • To test the hypothesis that the magnitude of hormonal alterations is influenced by the level of ED.

Main Methods:

  • Healthy young male volunteers (n=7) underwent a 20-day military field exercise.
  • Serum hormone concentrations (cortisol, growth hormone, insulin, testosterone) were measured.
  • Energy deficit (ED) was manipulated across three phases: 4000 kcal/day (P-I), 450 kcal/day (P-II), and 1000 kcal/day (P-III).

Main Results:

  • Initially, high ED (P-I) increased cortisol and growth hormone, while decreasing insulin and testosterone.
  • Hormonal levels largely recovered by later phases (P-II, P-III) with lower ED.
  • Testosterone levels increased above baseline by P-III, while thyroxine decreased and urine urea increased post-exercise.

Conclusions:

  • Lower energy deficits (below 1000 kcal/day) facilitate hormonal recovery during prolonged exercise.
  • Exercise intensity and resulting energy deficit significantly modulate hormonal responses in military personnel.
  • Findings suggest strategies to manage energy balance are vital for mitigating adverse hormonal effects during sustained physical demands.