For most of us, the "best" time of day to work out is simple: When we can.
Maybe that's before or after work. Or when the gym offers free daycare. Or when our favorite instructor teaches our favorite class.
That's why we call it a "routine." And if the results are the same, it's hard to imagine changing it up.
But what if the results aren't the same?
They may not be, according to a new study from a research team at Skidmore College. The results of a 12-week exercise program were different for morning vs. evening workouts.
Women who worked out in the morning lost more fat, while those who trained in the evening gained more upper-body strength and power. As for men, the performance improvements were similar no matter when they exercised. But those who did so in the evening had a significant drop in blood pressure, among other benefits.
The study is part of a growing body of research showing different results for different times of day among different populations. As it turns out, when you exercise can ultimately have a big effect. And we're not just talking strength and fat loss, but also heart health, mood, and quality of sleep.
An Accidental Discovery
The original goal of the Skidmore study was to test a unique fitness program with a group of healthy, fit, and extremely active adults in early middle age.
The program includes four workouts a week, each with a different focus: strength, steady-pace endurance, high-intensity intervals, and flexibility (traditional stretching combined with yoga and Pilates exercises).
But because the group was so large – 27 women and 20 men completed the 3-month program – they had to split them into morning and evening workout groups.
It wasn't until researchers looked at the results that they saw the differences between morning and evening exercise, says lead author Paul Arciero, PhD.
Arciero stresses that participants in every group got leaner and stronger. But the women who worked out in the morning got much bigger reductions in body fat and body-fat percentage than the evening group. Meanwhile, women in the evening group got much bigger gains in upper-body strength, power, and muscular endurance than their morning counterparts.
Among the men, the evening group had significantly larger improvements in blood pressure, cholesterol levels, and the percentage of fat they burned for energy, along with a bigger drop in feelings of fatigue.
Strategic Timing for Powerful Results
Some of these findings are consistent with previous research. For example, a study published in 2021 showed that the ability to exert high effort and express strength and power peaks in the late afternoon, about the same time that your core body temperature is at its highest point.
On the other hand, you'll probably perform better in the morning when the activity requires a lot of skill and coordination or depends on strategic decision-making.
The findings apply to both men and women.
Performance aside, exercise timing might offer strong health benefits for men with type 2 diabetes, or at high risk for it.
A 2020 study showed that men who exercised between 3 and 6 p.m. saw dramatic improvements in blood sugar management and insulin sensitivity, compared to a group that worked out between 8 and 10 a.m.
They also lost more fat during the 12-week program, even though they were doing the exact same workouts.
Train Consistently, Sleep Well
When you exercise can affect your sleep quality in many ways, says McMaster University neuroscientist Jennifer Heisz, PhD, author of Move the Body, Heal the Mind: Overcome Anxiety, Depression, and Dementia and Improve Focus, Creativity, and Sleep.
First, she says, "exercise helps you fall asleep faster and sleep deeper at night." (The only exception is if you exercise so intensely or so close to bedtime that your heart rate is still elevated.)
Second, "exercising at a consistent time every day helps regulate the body's circadian rhythms." It doesn't matter if the exercise is in the morning, evening, or anywhere in between. As long as it's predictable, it will help you fall asleep and wake up at the same times.
Outdoor exercise is even better, she says. The sun is the most powerful regulator of the circadian clock and works in tandem with physical activity.
Third, exercising at specific times can help you overcome jet lag or adjust to an earlier or later shift at work.
"Exercising at 7 a.m. or between 1 and 4 p.m. helps your circadian clock to 'fall back' in time, making it easier to wake up earlier," Heisz says. If you need to train your body to wake up later in the morning, try working out between 7 and 10 p.m.
All Exercise Is Good, but the Right Timing Can Make It Even Better
"The best time to exercise is when you can fit it in," Arciero says. "You've got to choose the time that fits your lifestyle best."
But context matters, he notes.
"For someone needing to achieve an improvement in their risk for cardiometabolic disease," his study shows an advantage to working out later in the day, especially for men.
If you're more focused on building upper-body strength and power, you'll probably get better results from training in the afternoon or evening.
And for fat loss, the Skidmore study shows better results for women who did morning workouts.
And if you're still not sure? Try sleeping on it – preferably after your workout.
Frontiers in Physiology: "Morning Exercise Reduces Abdominal Fat and Blood Pressure in Women; Evening Exercise Increases Muscular Performance in Women and Lowers Blood Pressure in Men."
Paul Arciero, PhD, professor, Health and Human Physiological Sciences Department, Skidmore College.
BMJ Open Sport & Exercise Medicine: "Diurnal variations in the expression of core-clock genes correlate with resting muscle properties and predict fluctuations in exercise performance across the day."
Physiological Reports: "Exercise training elicits superior metabolic effects when performed in the afternoon compared to morning in metabolically compromised humans."
Jennifer Heisz, PhD, associate professor, Department of Kinesiology, McMaster University.
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Cite this: Lou Schuler. What's the Best Time of Day to Exercise? It Depends on Your Goals - Medscape - Jun 20, 2022.