The best time to exercise is a hotly debated topic. Some people think that waking up early for a morning workout is best, while others believe that afternoon or evening is better. Instead of relying on opinions or bro-science, let’s look at some quality studies to see what the research suggests.
Savikj and colleagues looked at this issue in a randomized control study with eleven men. These participants had diabetes, a BMI around 23-33 kg/m2, and an average age of 45-68. They had the participants do two weeks of high-intensity interval training (HIIT) either in the morning (8 am) or in the afternoon (4 pm) three times per week (Mondays, Wednesdays, and Fridays).
The authors found that afternoon HIIT reduced the blood sugar in participants more than morning HIIT. Now keep in mind this study was limited to only men with diabetes. The results may be different in women and those without diabetes.
Mancilla and colleagues did a more in-depth study looking at a randomized trial with 32 men with diabetes or at risk. They also compared the effects of the morning (8-10 am) versus afternoon (3-6 pm) training. They found that compared to the morning group, the afternoon group had:
- Increased peripheral insulin sensitivity (+5.2 ± 6.4 vs. −0.5 ± 5.4 μmol/min/kgFFM, p = .03)
- Decreased insulin-mediated suppression of adipose tissue lipolysis (−4.5 ± 13.7% vs. +5.9 ± 11%, p = .04)
- Decreaesd fasting plasma glucose levels (−0.3 ± 1.0 vs. +0.5 ± 0.8 mmol/l, p = .02)
- Increased exercise performance (+0.40 ± 0.2 vs. +0.2 ± 0.1 W/kg, p = .05)
- Decreased fat mass (−1.2 ± 1.3 vs. −0.2 ± 1.0 kg, p = .03)
The issue with the above two studies was they did not control for the diet. Moholdt and colleagues did a parallel-group, randomized trial with three arms: control, morning, and evening exercise. They had all three groups eat a high-fat diet consisting of 65% of the calories from fat for eleven days.
The authors found that both the morning and evening group increased their oxygen consumption or VO2 max. However, the afternoon group also lowered their:
- Fasting and post-meal insulin
- Fasting sugars
- Nighttime sugars
When looking at specific types of lipids that promote atherosclerosis, such as sphingolipids, the authors found that evening exercise was best at lowering their levels.
So far, we have seen the effects of evening exercise be superior to morning exercise. The limitation of the above studies is their short-term nature. Let’s now look at a longer-term study. Teo and colleagues looked at 12 weeks randomized study comparing morning or evening exercise and the effects on Hemoglobin A1c, fasting sugars, and post-meal sugars. The study had 40 sedentary men with an average BMI of around 31, an average age of 51, and with or without diabetes.
At the end of the 12 weeks, the authors found no differences in the evening versus morning exercise for hemoglobin A1c, fasting sugars, or post-meal sugars.
It seems that over the long term, morning versus evening exercise impact may not be that different after all. So which one should you pick? Well, let’s answer this question a little differently.
When it comes to exercise, diet, or any other healthy lifestyle, habit formation is vital. So the question becomes whether morning or afternoon exercise is easier to stick with. In a study by Fournier and colleagues, they looked at 48 students trying to adopt a healthy behavior either in the morning or evening. They found that it took about 106 days for the morning group to form a habit versus 154 days for the evening group.
As you are thinking about how to apply the results of these studies into your own life, here are a couple of key points:
- There may be a slight metabolic advantage to afternoon/evening exercise in the short term, but it doesn’t matter as much in the long term.
- Morning habits are easier to stick to than afternoon/evening habits.
Ultimately, the key is to find the time and routine you can stick to! If morning makes it easier to do so, then I would recommend sticking to morning exercise.