Cortisol and growth hormone responses to exercise at different times of day.

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J Clin Endocrinol Metab 2001 Jun;86(6):2881-9 Related Articles, Books, LinkOut

Cortisol and growth hormone responses to exercise at different times of day.

Kanaley JA, Weltman JY, Pieper KS, Weltman A, Hartman ML.

Division of Endocrinology and Metabolism, Department of Medicine, University of

Virginia, Charlottesville, 22908, USA.

Exercise of appropriate intensity is a potent stimulus for GH and cortisol

secretion.

Circadian and diurnal rhythms may modulate the GH and cortisol responses to

exercise, but nutrition, sleep, prior

exercise patterns, and body composition are potentially confounding factors.

To determine the influence of the time of day on the GH and cortisol response to

acute exercise, we studied 10

moderately trained young men (24.1 +/- 1.1 yr old; maximal oxygen consumption,

47.9 +/- 1.4 mL/kg.min; percent body fat,

13.2 +/- 0.6%).

After a supervised night of sleep and a standard meal 12 h before exercise,

subjects exercised at a constant velocity

(to elicit an initial blood lactate concentration of approximately 2.5 mmol/L)

on a treadmill for 30 min on 3 separate

occasions, starting at 0700, 1900, and 2400 h.

Blood samples were obtained at 5-min intervals for 1 h before and 5 h after the

start of exercise; subjects were not

allowed to sleep during this period.

Subjects were also studied on 3 control days under identical conditions without

exercise.

There were no significant differences with time of day in the mean blood lactate

and submaximal oxygen consumption

values during exercise.

The differences over time in serum GH and cortisol concentrations between the

exercise day and the control day were

determined with 95% confidence limits for each time of day.

Exercise stimulated a significant increase in serum GH concentrations over

control day values for approximately 105--145

min (P < 0.05) with no significant difference in the magnitude of this response

by time of day.

The increase in serum GH concentrations with exercise was followed by a

transient suppression of GH release (for

approximately 55--90 min; P < 0.05) after exercise at 0700 and 1900 h, but not

at 2400 h.

Although the duration of the increase in serum cortisol concentrations after

exercise was similar (approximately

150--155 min; P < 0.05) at 0700, 1900, and 2400 h, the magnitude of this

increase over control day levels was greatest

at 2400 h.

This difference was significant for approximately 130 min and approximately 40

min compared to exercise at 1900 and 0700

h, respectively (P < 0.05).

The cortisol response to exercise at 0700 h was significantly greater than that

at 1900 h for about 55 min (P < 0.05).

A rebound suppression of cortisol release for about 50 min (P < 0.05) was

observed after exercise at 2400 h, but not

0700 or 1900 h.

Both baseline (before exercise) and peak cortisol concentrations were

significantly higher at 0700 h than at 1900 or

2400 h (P < 0.01).

We conclude that time of day does not alter the GH response to exercise;

however, the exercise-induced cortisol response

is modulated by time of day.

PMID: 11397904 [PubMed - indexed for MEDLINE]

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So maybe early morning exercise is not wise if you wish to lower the catabolic

hormone cortisol.

Anyone for sweat at 7PM?

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Good Health & Long Life,

Greg ,

http://www.ozemail.com.au/~gowatson

gowatson@...