Is too much HIIT making you anxious?

Along with all its physical benefits, high-intensity interval training can, in some cases, cause or worsen anxiety, says Brenda Rea, MD, PT, RD, family and preventive medicine physician at Loma Linda University Health in California.

“When you’re physically, emotionally, or psychologically stressed, your sympathetic nervous system is activated,” Rea explains.

That change floods your body with inflammatory cytokines (substances that are released by the immune system) and cortisol to prepare you for a fight-or-flight response. As a result, your heart rate may increase, you could start sweating, and you might have racing thoughts, she says.

Those mid- and post-workout symptoms are normal. But if you're predisposed to anxiety, you deal with a lot of stress outside of the gym, or you train too intensely, too often, the physiological effects of HIIT can sometimes cause lasting anxiety and the side effects that come with it, says Jessalyn Adam, MD, sports medicine physician at Mercy Medical Center in Baltimore.

You may notice changes in appetite, trouble sleeping, fatigue, inflammation, and an inability to relax, Rea adds. This is especially true if you log high-intensity workouts within a few hours of bedtime.

“Physical activity is typically considered eustress, or good stress, because it can be beneficial to the body,” Rea says. “But the minute you start pushing at a high intensity without adequate rest, that stress becomes dysfunctional and damaging.”

Here are three steps you can take to minimize HIIT-related anxiety—without sacrificing your fitness.