The short answer is whenever works best for you. The longer answer depends on your lifestyle, your commitments, how you sleep, and when you eat. But I think it’s simpler than that. The best time to run is the time you’ll do it consistently.
What the science says
Your body has natural rhythms, circadian rhythms, that affect how well you perform at different times of day. Body temperature, lung capacity and muscle function all peak in the mid- to late-afternoon, which is why science points to that window as optimal for athletic performance. Your muscles are warmer, your lung capacity can be up to 6% better than in the morning, and everything feels easier.
Early morning is the opposite. Body temperature is at its lowest, energy stores are depleted and your muscles are stiff. By most physiological measures, it’s the worst time to run.
And yet.
Why morning works anyway
I run at 5am because it’s the only time of day that belongs entirely to me before everything else starts. Nothing has come in yet. My diary is still clear. My decision is already made.
Early morning running has its own advantages that the performance science doesn’t fully capture. You start the day with something done. The mental reset that comes from an hour outside before work is harder to quantify than lung capacity, but it’s real. Research also suggests that running on an empty stomach can burn significantly more fat, and that people who exercise in the morning tend to make better food choices for the rest of the day.
The consistency argument is relevant here too. Mid- to late-afternoon might be the performance peak, but it’s also when life is most likely to get in the way. A meeting runs over, something comes up, the motivation that was there at 9am has gone by 4pm. Morning running has fewer variables.
Other times of day
Lunchtime runs work well for some people and I’ve enjoyed them when I’ve been able to fit them in and manage the logistics. Again, the main benefit is less about running performance and more about what it does for the rest of your working day, you come back sharper.
Evening runs are good for running off the day. The performance conditions are better than morning, and if you can find a running club or group, the social element adds something. The main risk is disrupting sleep if you run too late. This is worth paying attention to if you’re already struggling with rest.
What I’ve found
The science will tell you afternoon is best. Your life will probably tell you something different. What I’ve found is that the time of day matters less than the consistency of doing it at the same time. A 2012 study found that exercising at the same time every day produces greater physiological adaptations, it makes you fitter. Whatever time you pick, picking the same one repeatedly is worth more than optimising for peak body temperature.
For me that’s 5am. It took adjustment and the first few weeks weren’t easy. But I’d rather run harder at the wrong time of day than not run at all waiting for the right conditions.
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