Millions of Americans take time out of their busy schedule to train every day. But only 23% of adults over the age of 18 meet recommended guidelines for both aerobic and muscle-strengthening activity. The biggest obstacle for most people: not having enough time. In reverse, says a 2019 study by the CDC and Rand. Analyzing more than 30,000 participants, the study found that Americans have an average of more than five hours of free time per day.
Whether you are considering starting a training regimen or a more experienced athlete, one of the biggest questions I hear is, “When is the best time to train?” Most people are quite regimented and protective when exercising. Choosing to train in the morning or evening is often the product of a work schedule or childcare responsibilities. Or simply if one is a “morning person” or a “night person”.
But is there any science to support training in the morning versus training in the evening? A recent research study in Frontiers in Physiology has shed some light.
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Does the early riser get the exercise worm?
This was a relatively small study from Skidmore University that collected data from 27 women and 20 men who were already highly active on a regular exercise regimen. Participants were followed up for 12 weeks. They performed one of four different exercise routines – stretching, resistance training, interval sprinting, or resistance training – four times a week for an hour each time. One group performed the routine between 6:30 and 8:30 and the other group between 18:00 and 20:00
For the group that trained in the morning:
- Women had 7% greater belly fat loss, greater reduction in blood pressure, and greater leg strength
For the group that trained in the evening:
- Women experienced greater increases in upper body strength, power and endurance and improved mood
- The men had improved heart health, metabolic health, and emotional well-being
- Men also experienced greater weight loss and a reduction in blood pressure
Immerse yourself in other research
Previous studies examining the time-dependent effects of exercise were not consistent with the findings of this new study. Conversely, a small 2019 study found that men also had greater weight loss if they exercised in the morning. But several previous studies support the study’s current finding of improved metabolic health in men who exercised in the afternoon, including improved insulin sensitivity and blood sugar control.
An international consortium of researchers in January 2022 conducted a fascinating research study that looked at the molecular changes that occur in the cells of multiple organs in mice to try to quantify at the most basic cellular level what happens when you exercise in the morning compared to evening. Molecular profiles in mice showed greater dependence on fat to fuel morning exercise and greater dependence on glucose to fuel afternoon workouts. While some may argue that we cannot extrapolate the data on mice to humans, the cellular processes at the molecular level are similar.
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Additional factors that have been hypothesized to play a role include sleep quality and hormones.
The role of sleep
One possible explanation is that women tend to spend more time in deep sleep and therefore tend to be more alert and ready to exercise early in the morning. But there are many men who also prefer to exercise in the morning. This brings us to one of the biggest sleep and exercise myths; that working out too late in the evening or before bed will lead to a reduction in sleep quality. Again, it depends. Exercise at the end of the day may not affect those night owls who call themselves. And most importantly, a meta-analysis identified 29 studies that showed exercise improves sleep quality or duration.
Don’t count hormones
Levels of the stress hormone cortisol are highest for both men and women in the morning. This could generate the need to “burn” stress for both men and women who prefer to do cardio workouts early in the morning. Cortisol, however, can have an inhibitory or catabolic effect on muscle building. So men and women whose focus is strength training could see more benefits with evening workouts.
It is also worth mentioning that the most recent study found that macronutrient consumption did not play a role. Study participants were also required to follow the exact same diet of foyr’s meals a day at the same time for 12 weeks.
The ‘X’ factor: you do it
Bottom Line: This was a small study, and there’s still a lot we don’t know about the time-dependent benefits of exercise. It adds to the body of evidence that the metabolic benefits are greater for men who exercise in the evenings. For women whose goal is to burn fat, this study showed a clear benefit for a morning workout. And I think we cannot ignore the catabolic effects of cortisol; for men and women whose goal is to increase strength, an evening workout may be preferable.
Whether you work out in the morning or in the evening, the key point is that you are exercising and you will surely benefit from it. If you feel better mentally and enjoy working out first thing in the morning, then keep it up! If you have a specific goal in mind, consider your study results when choosing the time of day to train.
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Michael Daignault, MD, is a board-certified emergency room physician in Los Angeles. He studied Global Health at Georgetown University and has a medical degree from Ben-Gurion University. He completed his emergency medicine training at Lincoln Medical Center in the South Bronx. He is also a former United States Peace Corps volunteer. Find it on Instagram @ dr.daignault