Working out may boost your testosterone and growth hormone naturally, but does that lead to increased muscle strength?
Not according to two new studies by researchers at McMaster University. While the levels of those hormones in the blood do jump after resistance exercise, they don’t play a large role in stimulating muscle growth.
In one study, published in Journal of Applied Physiology, the researchers looked at the difference between men and women after intense resistance leg exercise. Men, of course, showed a much larger increase in their testosterone—45 times greater.
The muscles of both men and women, however, built new muscle proteins at about the same pace.
According to the researchers, while testosterone can promote muscle growth at extremely high doses, their research showed that “naturally occurring levels of testosterone do not influence the rate of muscle protein synthesis."
In the second study, published in the European Journal of Applied Physiology, researchers put 56 men through a 12-week strength-training program.
The men increased both muscle strength and mass throughout the training, but post-exercise spikes in testosterone and growth hormone had little effect on these changes.
Researchers did find that growth hormone—along with the stress hormone cortisol—was linked to an increase in muscle fiber size. Jumps in cortisol—which is generally thought to have the opposite effect of growth hormones—was also associated with larger muscle mass.
It’s common sense that you need to work out to get ripped, but the researchers warn against focusing solely on boosting your growth hormones.
"The idea that you can or should base entire exercise training programs on trying to manipulate testosterone or growth hormone levels is false," study author Stuart Phillips said in a news release.