Uh, Do High-Impact Workouts Mess With Your Hormones?

At its best, exercise bolsters heart health, fights depression, and supports longevity. But too much of a good thing can swing in the opposite direction. As any athlete knows, overdoing it in the gym can lead to injury and even hormonal disruptions.

Exercise, when done right, "gives your hormones a workout," says Nicky Keay, M.B., a sports endocrinology researcher and author of Hormones, Health, and Human Potential. 

Working out increases growth hormone, which is key to healthy body composition and increases insulin sensitivity, which helps regulate blood sugar, Keay says. It triggers the release of dopamine and serotonin, well known for their mood-boosting effects. Exercise also boosts estrogen1, a reproductive hormone whose decline is to blame for many menopause symptoms, and testosterone, which supports everything from bone health to libido. Several studies have demonstrated that regular exercise can relieve menstrual pain2, which can at least in part be explained by increased progesterone, which has anti-inflammatory effects.

Exercise generally lowers cortisol levels, though exact effects depend on the type, intensity, duration, and timing of exercise. One meta-analysis found that HIIT workouts increased cortisol in the short term (30 to 60 minutes after) but decreased cortisol levels below baseline within two hours of the workout, with levels returning to normal after 24 hours. Researchers noted that the time it takes for cortisol levels to come back down to earth is longer with HIIT workouts than other less intense workouts. Another study found that cortisol decreased over time with endurance exercise, (cycling for 40 minutes at 75% of maximum heart rate) but decreased more slowly with resistance exercise (30 to 40 minutes of repeating sets of 10 of a series of exercises). 

According to Keay, if high-intensity workouts are done too often, with too little rest or proper nutrition, they can spur an overproduction of cortisol. 

She says this is particularly likely when one does high-intensity workouts early in the morning before eating anything. Cortisol is already highest in the morning3, and working out on an empty stomach puts the body in a state of stress, further increasing cortisol, Keay says. 

The question that's left, then, is whether this increase in cortisol has negative effects, like the weight gain that people warn about on social media. 

Keay is decisive. She says that while overexercise may not cause weight gain, "it certainly won't help you lose weight." She sees it often in her work with people with relative energy deficiency in sports, or RED-S, a condition that occurs when athletes exercise too much without adequate nutrition. 

Disruptions extend to other hormones whose imbalances are further reinforced by an excess of cortisol. "Cortisol tends to be the dominant hormone for evolution reasons, running away to quickly escape danger…cortisol reinforces the downregulation of the other ones," Keay says. 

Levels of human growth hormone will dip, which will do no favors for body composition. Estrogen is also at risk. Overexercising famously causes amenorrhea, or the loss of a menstrual period. It requires a lot of energy for the body to produce reproductive hormones, so if you're pushing yourself to your limits and not properly fueling, these hormones are some of the first to go, Keay explains.