Evening workouts can disrupt sleep and morning sessions build consistency. Here is the full expert breakdown.
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For adults in their 60s and 70s focused on living longer and sleeping better, the time of day you move may matter nearly as much as the workout itself. A large analysis published in Nature points to a specific window that appears to deliver the biggest cardiovascular payoff for older adults.
A study of more than 90,000 people found that working out in the afternoon reduces the risk of heart disease or early death more than physical activity in either the morning or evening. The benefits were most pronounced for men and seniors.
How exercise and cortisol are connected
Cortisol is a steroid hormone secreted by the adrenal glands. It drives the body’s natural daily rhythm, rising in the morning to energize and tapering off at night to promote sleep. Nearly every tissue in the body responds to it.
Dr. Anne Friedlander, an exercise physiologist who leads the Movement and Exercise pillar at Stanford Lifestyle Medicine, says consistent movement helps keep that rhythm intact.
“We all know that exercise reduces our long-term risk for disease, but perhaps many don’t understand why,” Friedlander told Stanford Medicine.
She added that one contributor to that disease-fighting benefit is a reduction in chronically elevated cortisol, and that regular movement gives the hormone room to rise, lower and settle back into balance.
Chronic stress breaks that pattern. “Cortisol has a bad reputation, but it serves important functions in the body. Basically, you want it to be high when it is supposed to be high and low when it is supposed to be low. The problem with cortisol in response to chronic stress is that it flattens out those highs and lows, so your body no longer responds normally,” Friedlander said.
Why workout timing matters for your body clock
The circadian rhythm is a 24-hour internal clock that regulates eating, sleeping and key physiological processes. It is set primarily by light and dark, though sleep habits, meal times and stress also shape it. Moving in sync with that rhythm can sustain energy and support recovery.
Erin Nitschke, an ACE Certified Health Coach and Fitness Nutrition Specialist, told ACE Fitness, “The human body likes balance and predictability. When its natural processes are disrupted, the body has to reorganize and compensate for whatever deficiencies have developed as a result of an unexpected or inconsistent stimulus.”
The case for morning workouts
Breathing, heart rate and nearly every hormone operate on a cycle, and morning workouts align with the body’s natural cortisol peak. That lets the hormone run its course rather than spiking later in the day.
People who train in the morning also tend to be more consistent, finishing the session before meetings, errands and family obligations crowd it out.
The case for afternoon workouts
The Nature finding gives older adults a strong reason to lean into mid-day movement, especially given how much the cardiovascular benefit skewed toward men and seniors. Most people hit an energy slump around 3 p.m., and afternoon exercise can counteract it. But Bronwyn Bacon, N.D. of Elevate Health, told ACE Fitness the research resists a single answer.
“The research is all over the map on the best time to exercise, mainly because research is looking at all different types of benefits from stress management to weight loss and body composition. For example, with weight loss I have seen evidence that supports morning exercise being best, whereas I’ve seen research that suggests afternoon workouts are best for building muscle mass. For this reason, I think it’s hard to pin down a specific time that is ‘best.’ In the end, we are far too sedentary of a society and we are overworked, so I think it’s good to get exercise in when you can based on your schedule.”
Why evening workouts can work against you
Vigorous evening exercise can disrupt the circadian rhythm and delay melatonin production, a sleep concern that often grows more pressing with age. Carol Harrison, a senior exercise physiologist, told MD Anderson the effect sets in fast.
“Research has found that if you do vigorous exercise in the evening, it delays the production of melatonin the next night, making it harder to fall asleep. What’s surprising is that the change happens so quickly, after only one night of exercise,” Harrison said.
Harrison noted that research into how exercise affects the body clock is still in its early stages, but a connection seems clear. MD Anderson recommends saving high-intensity workouts for earlier in the day and sticking to lower-intensity movement at night.
What to do if an afternoon slump hits
Bacon told ACE Fitness that an afternoon slump can mean different things for different people, and the right response depends on the cause.
“Some people have an afternoon slump due to recent high stress or depression. For these people, exercise could be excellent to boost energy. In contrast, someone who is having chronically low cortisol from long-term stress would do better with rest and meditation. An ‘afternoon slump’ could suggest an abnormal dip in cortisol, but it can also be due to many other things, such as high stress levels or poor eating choices.”
Morning sessions do not suit everyone. Shift workers, night owls or those with later schedules may fare better with a midday or early afternoon workout.
This article was created by content specialists using various tools, including AI.
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Hanna Wickes is a content specialist working with McClatchy Media’s Trend Hunter and national content specialists team.