Cortisol: Good or Bad?

Every bodybuilder has heard that you must keep training sessions to less than 45 minutes because after that, cortisol levels kick in.

on the newest study in the Journal of Applied Physiology, the rise in cortisol might not be such a bad thing! Researchers examined 56 healthy (but untrained) young men who took part in a 12-week resistance-training program.

The researchers measured testosterone, growth hormone (GH), IGF-1, and cortisol concentrations at the end of the program. If increases in testosterone and GH was the sole variable for increased muscle growth, then those with the highest levels should have made the most improvements in muscle mass, but they didn’t. The biggest winners appeared to be GH and cortisol.

The lifters with the biggest post-workout spikes in cortisol were associated with gains in type-II muscle size but it was also the only hormone associated with greater gains in lean body mass.

So if keeping training programs to less than 45 minutes to minimize cortisol was the key to muscle growth, the group with the largest increases in testosterone should have been the clear winner, but surprisingly the group with the largest post-exercise increases in cortisol made bigger improvements in muscle hypertrophy.

According to Daniel West, the lead author of the study, “The idea that you can or should base entire exercise training programs on trying to manipulate testosterone or growth hormone levels is false. There is simply no evidence to support this concept.”

REFERENCE: West, D.W.D., Jof Appl Physiol., 112 (11): 1805, 2012.