When Should I Exercise? Intense Exercise Study Reveals How Evening Workouts Impact Sleep

In the past, nighttime exercisers have been issued a warning: going hard around bedtime could lead to sleep issues that may outweigh the benefits of the workout. But fortunately, more and more papers, including one published Wednesday in Experimental Physiology are starting to prove that this myth is based on shaky ground. Like the late night meal, the evening workout may not be as harmful for sleep as it’s made out to be, and may actually confer an added benefit.

While this study isn’t evidence that’s it worth going straight to bed post-run, a trial conducted by P.h.D student Penelope Larsen, in tandem with Frank Marino, Ph.D., the head of Charles Sturt University’s School of Exercise Science and suggests that hard workouts won’t actually impact sleep quality, which does fly in the face of some of the conventional wisdom suggesting that increases in body temperature, heart rate, and adrenaline make intense evening workouts a recipe for sleeplessness. Although Larsen’s trial was only on a small group of all-male individuals she suggests that it opens the door to more flexibility when it comes to workout times.

In her trial, Larsen had her 11 participants perform high-intensity cycling workouts designed to let each person really go for it — each person complete one minute all-out sprints with four minutes of rest in between each one. Participants completed that challenge at three different times on separate days — either in the morning between 6 a.m. and 7a.m., in the afternoon between 2p.m. and 4p.m., and in the evening between 7p.m. and 9p.m. Each evening, she monitored their sleep cycles, and noted that there were no significant differences in how each person slept regardless of whether they exercised in the morning, afternoon or evening.

Larsen’s trial fits with a growing body of research that is looking to address the idea that intense workouts lead to sleep disruption patterns. Though this study cites a 2001 report from the American Academy of Sleep medicine which recommends avoiding high-intensity exercise before sleep, the AAS has actually updated their stance slightly. Currently, the agency suggests that recent research regarding how exercise impacts sleep has been inconclusive. Overall, their recommendations suggest that insomniacs avoid exercising aggressively before bed, but add that it might be fine for “good sleepers” to get some sprint work in.

But while Larsen found that exercise timing had little effects on sleep, she found that exercise timing did have effects on other measures. For instance she noted that evening exercise decreased the amount of ghrelin — a hormone that regulates hunger — in her participants. Theoretically, this should have led to decreases in appetite, though she didn’t note any in the paper. Still, the effect was significant enough to warrant special note. In the paper, Larsen notes that this needs to be looked into more thoroughly, but suggests that evening exercise can “favorably alter appetite-related hormone concentrations.”

"“Participants were able to perform better during latter parts of the day."

But more interestingly, she found that it had small effects on how much power her cyclists were able to generate on specific intervals. On average, there weren’t significant differences between power output in the morning, afternoon and evening — though the afternoon and evening power out puts were slightly higher than the morning numbers. But there were differences in how they performed on the first two trials. The cyclists were able to put put out significantly higher power on the first and second intervals of the workout that they could in the morning.

“Interestingly, power output during the sprint efforts was higher for the afternoon and evening trials compared to the morning trial, indicating that participants were able to perform better during latter parts of the day,” Larsen added. “Therefore, time-of-day may also need to be considered when planning training schedules.”

At least for her trial, Larsen adds that the paper just adds credence to the idea that it’s not worth fighting when your body prefers to exercise, both for sleep purposes, and for performance. For those who would rather not punish themselves in the early hours of the morning, making time for a run in the evening may be just as good an alternative.