The case for the nighttime workout

HIIT in the evening could actually help you sleep better.

Some experts say a mid-day workout is optimal since it can prevent an afternoon energy slump and increase productivity. Exercising too close to bed, other researchers warn, could be linked to nightmares or night sweats. However, if it's more convenient to go to the gym after work, there's a case for the nighttime workout, too. A growing body of research has shown that evening exercise does not negatively impact shut-eye and in fact, sleep quality improves for some athletes. The proof is in the numbers: The National Sleep Foundation surveyed 1,000 adults about sleep and exercise habits. Ninety-eight percent of them said their sleep quality remained the same or improved on workout days, even after night sessions.

Separately and on a smaller scale, sleep researcher Shawn Youngstedt, Ph.D., professor at Arizona State University’s College of Nursing and Health Innovation, studied 20 sedentary insomniacs. They did aerobic exercise and strength training two hours before bed, then had their sleep monitored. (He also monitored them on an exercise-free night.) Eighteen out of 20 people “slept an hour or two more or had no change after exercise,” Youngstedt says and he speculates the results would be similar for a healthy, fit population.

In addition to moderate aerobic and strength exercise, even HIIT is on the table: A study in The Journal of Sleep Research showed that subjects slept just as well on nights when they vigorously exercised as they did on nights when they did not exercise at all.

Here's why: “There is a relaxation component post-exertion which some people report as helpful,” says sleep expert Michael Breus, Ph.D., author of The Power of When. What is more, while exercise can raise your core body temperature, studies found that this is not detrimental to sleep quality.

Still, athletes can respond differently to the type and timing of exercise. If you want to shift your morning or mid-day workout routine to nighttime, follow these three guidelines initially:

1. Experiment
Vary workouts (running, gentle yoga) and times (two hours or 30 minutes before bed) to see how they’ll affect your slumber. “Play around with the duration and the intensity to find out what is best for you,” says Jessica Matthews, M.S., The American Council on Exercise's senior advisor for health and fitness education.

2. Monitor
Fitbit, Apple Watch, and the S+ Sleep Tracker (which sits on your nightstand) can track sleep quality and duration, so you can compare your rest on workout and non-exercise nights, says Matthews.

3. Journal
At night, write down how you exercised and how you felt. In the morning, record how well you slept (based on tip two above).