Is it better to exercise in the morning or at night?
It’s a debate that’s raged in fitness forums for years. Research on the topic has been decidedly mixed, with studies comparing the timing of physical activity finding modest benefits in both directions. Now, new research to be presented at the American College of Cardiology’s Annual Scientific Session later this month finds people who are more likely to hit the treadmill instead of the snooze button might have an edge.
Researchers led by cardiologist Prem Patel of the University of Massachusetts Chan Medical School analyzed data from Fitbit fitness trackers worn by more than 14,000 participants (don’t worry, they opted into the study). This allowed them to identify periods when their heart rates were elevated for at least 15 minutes, group participants by when they exercised, and later compare a variety of measures of their cardiovascular health.
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“In the past, researchers have mainly looked at how much physical activity to do, the number of minutes, or the intensity of physical activity,” Patel said in a statement. “Now with one in three Americans having a wearable device, we’re gaining the ability to look at exercise at the minute-by-minute level, and that opens a lot of doors in terms of new analyses.”
They found that morning exercisers were 31 percent less likely to have coronary artery disease, 18 percent less likely to have high blood pressure, 21 percent less likely to have high cholesterol, 30 percent less likely to have Type 2 diabetes, and 35 percent less likely to have obesity. “If you can exercise in the morning, it seems to be linked with better rates of cardiometabolic disease,” said Patel.
Still, the researchers stress that this finding is only an association. Biological factors like hormones, sleep, and genetics could play a confounding role, as could behavioral or psychological factors. For example, people who prioritize healthy living in general might be more likely to get an early workout.
While the debate about morning versus evening workout times will continue to live on, there’s one thing that all experts agree on: Getting some kind of physical activity is key to better health outcomes. “Any exercise is going to be better than no exercise,” said Patel.
So if you’re considering adopting a new exercise regimen, don’t sweat the timing. Just get out there and move. 
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