John Davis

Written by John Davis


When is the Best Time of Day to Run

Most runners tend to feel sluggish when they run early in the morning and more “snappy” in the afternoon or evening.

But how big is this effect? Are your morning runs listless because you just rolled out of bed, or is there a deeper physiological root?

There are a lot of biological rhythms that follow a 24-hour “circadian cycle”; in fact, there’s an entire field of biology called chronobiology devoted to the study of these phenomena. Because of that, there are several high-quality articles on how your daily circadian rhythm affects your athletic performance.

So, in today’s article, we’re going to look at the research about the ups and downs of the time of day and how it affects your performance to determine when is the best time of day to run.

The research on running performance and time of day

The bulk of the early work on circadian cycles was focused on worker productivity and sleep issues. It wasn’t until the 1980s that a body of research began to develop around maximal athletic performance.

One study from this era, conducted by Claire Baxter and T. Reilly at Liverpool Polytechnic in the United Kingdom, investigated the variability in performance over 100m and 400m all-out swims (duration-wise, roughly equivalent to a 400m and 1600m running race) over a period of several days. Swimming is conducive to this type of study because the effects of lighting, temperature, and weather can be eliminated.

Fourteen competitive swimmers were tested over the two distances at 6:30 am, 9:00am, 1:30 pm, 5:00pm, and 10:00pm. Baxter and Reilly found that swimming race times decreased steadily throughout the day; 100m swims were 3.5% faster and the 400m swims were 2.5% faster at 10pm vs. 6:30 am.

The swing in times was also closely related to the change in internal body temperature, which is at its nadir at around 5am and peaks around 8 pm. Since there were no tests between 5pm and 10pm, the authors hypothesized that they may have missed the true peak in performance if it occurred at the same time as the peak in body temperature.

Studies of this type and design piled up over the years, as researchers investigated athletes of all types, even NFL football players (one study found that west coast football teams have a distinct advantage over east coast teams in Monday Night Football matchups). Unfortunately, I could not find any good studies on well-trained runners.

But a pair of review studies published by another group of researchers in the UK in 2005 sifted through the reams of research to identify overall trends. In the first, Drust et al. methodically demonstrate that performance in skill-based activities, like serving a tennis ball or balancing on one leg, is higher in the morning, while performances in strength and endurance-based activities steadily follows the body’s internal temperature, peaking in the early to mid-evening.

Peak performance and body temperature

In the second review, the same team of researchers discussed some of the more practical aspects of measuring variations in body temperature and athletic performance, and ultimately demonstrated that the rise and fall of body temperature is not so much because of differences in metabolic activity, but is from changes in blood flow to the limbs.

After you awaken, your body is in a “heat gain” mode to increase its core temperature, so the body shunts blood flow to the extremities. In the late afternoon and early evening, your body is in a “heat loss” mode and blood flow to the extremities is increased.

It’s unclear whether this is the primary cause of increased athletic performance in the late afternoon and evening, but it makes sense from a physiological point of view: in the evening, your body is already primed for shedding excess heat, which is a necessary part of exercise. We know from studies on exercise in hot temperatures that your brain appears to limit your body’s ability to perform when it can’t get rid of excess heat fast enough.

However, other factors probably play a role too, since various hormone levels are known to fluctuate throughout the day as well (a point made by Waterhouse et al.). Some additional questions arise when we begin to consider the ideal time to schedule an event in the heat: should it be in the evening, when the body’s thermal radiator is already primed? Or should it be in the morning, when there is more “headroom” between the body’s set temperature and the maximum safe temperature tolerable during exercise? This is an issue that’s yet to be resolved with research.

Final thoughts

Complicated scenarios like the one above notwithstanding, the body of scientific literature is pretty clear that your peak running performance—all else, including weather and temperature, being equal—is in the mid-afternoon and into the evening, perhaps even as late as 8 or 10pm.

As with many things in exercise physiology, it seems that the top-level athletes and coaches already had this one figured out a long time ago. Most world record attempts are held in the evening or at night, though temperature and wind speeds in the spring and summer are lower in the evening too. After reading these studies, I wonder if we will see any records or top performances from marathons held in cool regions in the late afternoon or early evening. It appears that you can boost your performance simply by moving your race time from the early morning when body temperature is low to the evening when it is higher.

Unfortunately, due to the absence of any high-quality running-specific studies on endurance and the circadian cycles, it’s hard to say how large that boost would be. Given the results of Baxter and Reilly, however, I’d bet it’s on the order of 1-2%, which could be 10-20 seconds over 5km!

These findings also apply to workouts: if you are doing a hard workout in the morning, expect it to be somewhat slower than if you were running it in the evening.

While we stick to the purely scientific and research-driven findings in these articles, obviously some runners have a preference for running in the morning and find getting the workout out the way feels better and prevents taking the day off after a long, hard work day. A good friend of the RunnersConnect team, Greg Strosaker of PreDawn Runner, wrote a piece on NoMeatAthlete about the benefits of running in the morning along with some great tips on how to make it more enjoyable and easy to do.

As always, more research is needed, but these studies are probably good news for the night runners out there!

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1. Baxter, C.; Reilly, T., Influence of time of day on all-out swimming. British Journal of Sports Medicine 1983, 17 (2), 122-127.
2. Smith, R. S.; Guilleminault, C.; Efron, B., Circadian rhythms and enhanced athletic performance in the national football league. Sleep 1997, 20 (5), 362-365.
3. Drust, B.; Waterhouse, J.; Atkinson, G.; Edwards, B.; Reilly, T., Circadian Rhythms in Sports Performance—an Update. Chronobiology International 2005, 22 (1), 21-44.
4. Waterhouse, J.; Drust, B.; Weinert, D.; Edwards, B.; Gregson, W.; Atkinson, G.; Kao, S.; Aizawa, S.; Reilly, T., The Circadian Rhythm of Core Temperature: Origin and some Implications for Exercise Performance. Chronobiology International 2005, 22 (2), 207-225.

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3 Responses on “When is the Best Time of Day to Run

  1. Thanks for the mention John, and you had to know I’d weigh in on this topic! As you said, much of when we train depends on the time of day that best fits into our schedule (since most of us fit running around our other commitments), and I think that over time you adjust a bit to this rhythm – though I doubt I could find many studies to support that. I will say that when I want to really deliver on a key workout, I tend to wait until lunch. Another factor that dictates workout performance to me is fueling and nutrition through the day – for some reason, I tend to run on empty come evening, and I fade pretty quickly on the rare occasion that I do run late at night. Maybe getting up early (which I do even when I don’t run) means that my peak time is a bit earlier than the 8PM period, and the energy just begins to fade after that. Regardless, this is an interesting article, and I too am curious as to whether we’ll see any move to afternoon marathons where the climate encourages it.

  2. Interesting that the best time to run is in the evening and yet, mainstream fitness sources suggest not exercising too close to bed time. I wonder how that factors into these studies, if at all.

    • That is true, great point there, although we are recommending earlier in the evening, whereas experts suggest you should not run within a few hours of going to bed, as most people go to bed around 11pm, a 5 or 6pm run would allow enough time for your body to calm down. Interesting point though, thank you for creating some discussion! The 10pm runs may be a little too risky for most!

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