Sticking to a regular workout routine is good for your heart, mental health, and other aspects of your body. But, how does hitting the gym affect your testosterone levels? It’s a little complicated.

Some exercises can raise your testosterone, while others can lower it. The effect on your testosterone levels also depends on how intensely you’re working out and for how long, explains Anthony Hackney, Ph.D., D.Sc., a professor of exercise physiology and nutrition at the University of North Carolina, who’s studied exercise and testosterone for decades.

Testosterone, which is the main male sex hormone that’s produced by the testicles, is anabolic and does help you build muscle. (That’s one of its functions, anyway.) But other hormones also contribute to muscle-building and endurance.

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“While testosterone is important, it’s not the only way the body decides to create an anabolic response,” Hackney adds.

Testosterone is vital for other bodily functions, like bone strength, hair growth, sperm production, and libido. And, your T levels fluctuate throughout the day, says Jamin Brahmbhatt, M.D., a urologist at Orlando Health.

Read more: Men’s Health