Here's Why the Time of Day Matters When Exercising

Do you go for a jog first thing in the morning, or do you hit the gym after work or in the evening? Your answer may affect the type of results you achieve, according to two new studies.

One team of researchers in the first study found that overall exercise performance was about 50 percent more efficient toward the end of the day — or in the evening — compared to the morning hours. In the second study, the most beneficial effect of exercises — as measured by metabolism — is during the late morning.

The bottom line could be: “You may be a morning person, or you may be a night person, and those things have to be taken into account,” according to Paolo Sassone-Corsi, senior author one of the studies, who is with the Center for Epigenetics and Metabolism at the University of California, Irvine. That means that the new research appears to conclude that your circadian rhythm, or your internal clock that is synonymous with sleep patterns, is a factor in how your body responds to physical exertion.

The findings are key to helping people start and maintain a successful exercise routine. However, the researchers in both studies, published this month in the journal Cell Metabolism, used mice to look at the link between time of day and exercise performance. The researchers conceded that translating the findings toward humans was challenging because mice in a lab have different “internal clocks” then people.

Nonetheless, one team of researchers found that a protein called “hypoxia-inducible factor 1-alpha” (HIF-1) is activated by exercise in different ways, depending on the time of day. HIF-1 is a factor in the production of oxygen levels in tissue — and overall energy in the body. The HIF-1 component is now considered a key to determining the best time of day to exercise for a given individual, but more research is required.

“It makes sense that HIF-1 would be important here, but until now we didn’t know that its levels fluctuate based on the time of day,” Mr. Sassone-Corsi said. “This is a new finding.”

Meanwhile, primary care physicians urge patients to carefully determine the best time of day to exercise and the intensity of the exercise. That process takes time and commitment, says Deepa Sharma, D.O., a family medicine physician with Baptist Health Primary Care.

“It’s important to recognize that you have not been active and to slowly move forward,” says Dr. Sharma. “I usually tell my patients that if you’re not moving around much, anything you do is better than nothing — and to be forgiving of yourself. So when you get up, it’s unreasonable to think you’re going to suddenly be able to exercise for 60 minutes and not feel sore the next day.”

For overall cardiovascular health, the American Heart Association recommends at least 30 minutes of moderate-intensity aerobic activity, five days per week, for a total of 150 minutes. But many studies have found that even less amount of time spent doing physical activity can be beneficial.

“Tell yourself that even if you did exercise, say I could only do 10 minutes today, that was ten minutes more than I could do yesterday,” explains Dr. Sharma. “And know that it’s a long-term goal and that these kind of changes do take time — but stick to it and do what you can.”