Does cortisol increase muscle loss?
It's a popular idea that high levels of cortisol promotes muscle
loss. However, there is evidence to show that despite elevated levels
of cortisol, muscle loss is not inevitable.
Cortisol levels following several months of aerobic exercise, for
example, are far higher than when aerobic exercise and weight training
are combined.
Some evidence for this comes from a trial published in the Journal
of Applied Physiology [1]. A group of 31 women was assigned
to one of four groups.
• The first group served as a control group, and did nothing.
• Group two followed a low-fat, high-carbohydrate diet.
• Group three combined the diet with aerobic exercise.
• The fourth group combined diet with aerobic exercise and
a regular strength training program.
When cortisol levels were measured at the end of the study, they
had risen by an average of 51% in group three (the group combining
diet and aerobic exercise). The women who combined aerobic exercise
with a strength training program only experienced a 10% rise.
However, the loss of body fat was greatest in the women who combined
a low-calorie diet with aerobic exercise. They also gained more
muscle (3.1 pounds) than the women who trained with weights, who
actually lost 3.7 pounds of muscle.
In a similar study, moderately obese subjects were assigned to
one of three groups: diet plus strength training, diet plus aerobic
training, or diet only. Subjects in the two exercise groups trained
three times per week [2].
After eight weeks, the average amount of weight lost, 19.8 pounds,
did not differ significantly among groups. The strength-training
group, however, lost significantly less muscle than the aerobic
and diet-only groups.
Reference
1. Kraemer, W.J., Volek, J.S., Clark, K.L., Gordon, S.E., Incledon,
T., Puhl, S.M., Triplett-McBride, N.T., McBride, J.M., Putukian,
M., & Sebastianelli, W.J. (1997). Physiological adaptations
to a weight-loss dietary regimen and exercise programs in women.
Journal
of Applied Physiology, 83, 270-279
2. Geliebter, A., Maher, M.M., Gerace, L., Gutin, B., Heymsfield,
S.B., & Hashim, S.A. (1997). Effects of strength or aerobic
training on body composition, resting metabolic rate, and peak oxygen
consumption in obese dieting subjects. American
Journal of Clinical Nutrition, 66, 557-563
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