It is a widely held belief that exercising in the evening can interfere with sleep quality, but a new Swiss study shows this is generally not the case.

Researchers from the Institute of Human Movement Sciences and Sport at ETH Zurich (Swiss Federal Institute of Technology in Zurich) analyzed 23 studies on the subject. They found that engaging in moderate exercise within four hours of going to bed does not have a negative effect on sleep — and may even help a little.

“If doing sport in the evening has any effect on sleep quality at all, it’s rather a positive effect, albeit only a mild one,” said Dr. Christina Spengler, head of the Exercise Physiology Lab at ETH Zurich.

The findings show that following an evening of physical activity, study participants spent 21.2 percent of their sleeping time in deep sleep. After an evening without exercise, however, the average time spent in deep sleep was 19.9 percent.

Although the difference is small, it is statistically significant. Deep sleep phases are especially important for physical recovery.

The one exception to the rule was vigorous training within an hour before bedtime. According to this analysis, it is the only type of evening exercise that may have a negative effect on sleep quality. “However, this preliminary observation is based on just one study,” Spengler said.

One example of vigorous training is the kind of high-intensity interval training that competitive athletes would do. In many cases, though, a longer endurance run or a longer ride on a racing bike would fall into the moderate training category.

“As a rule of thumb, vigorous training is defined as training in which a person is unable to talk. Moderate training is physical activity of an intensity high enough that a person would no longer be able to sing, but they could speak,” Spengler said.

In general, study participants who had completed an intensive training session shortly before bedtime took longer to fall asleep. This essentially happened because participants were not able to recover sufficiently in the hour before they went to bed — their hearts were still beating more than 20 beats per minute faster than their resting heart rate.

Moderate exercise did not cause sleep problems in any of the studies examined, not even when the training session ended just 30 minutes before bedtime.

According to the official recommendations of sport physicians, people should engage in at least 150 minutes of moderate exercise each week. The new findings suggest that people shouldn’t worry about sleep if they only have time to exercise in the evenings.

“It is well known that doing exercise during the day improves sleep quality,” Spengler said, adding: “Now we have shown that, at the very least, exercising in the evening doesn’t have a negative effect.”

The researchers point out that they looked at average values over the course of their analysis, which made only general statements possible.

“Not everyone reacts to exercise in the same way, and people should keep listening to their bodies,” said Jan Stutz, a doctoral student in Spengler’s research group and lead author of the analysis. “If they notice they are having problems falling asleep after doing sport, they should try to work out a little earlier.”

The findings are published in the journal Sports Medicine.

Source: ETH Zurich