So what is the best time of day to run? Good question. Whether you are a recreational runner or someone who races competitively, we can likely all agree on one thing: running can be difficult no matter what time of day it is! Most of us have probably noticed that heading out for a run at certain times of the day seems to make our efforts feel slightly easier. You aren’t wrong and there are some scientific reasons why this is. Let’s explore…
You’ve likely heard this one before. We all have them. These small fluctuations in the performance of bodily functions operate on a 24-hour basis. There are over 100 circadian rhythms that scientists measure, but body temperature, lung performance, and energy stores seem to relate most directly to running.
Morning time is when body temperature is at its lowest, so muscles may feel stiff. Lung function is at its weakest then as well. And since we haven’t eaten in several hours, our energy stores are depleted. The ol’ circadian rhythm is likely working against you on that 5:30 am run!
Lunchtime brings another dip in body temperature and lung function, so running then isn’t optimal from a scientific standpoint. Mid to late afternoon just may be the sweet spot. This is when body temperature peaks and lung function is improved by as much as 6%. Do you feel like running after a long day of work? Probably not, but give it a try. Your muscles will be looser and you may ultimately need to give less effort to maintain (or improve) your pace!
You are unlikely to talk to any runner who doesn’t have some choice words about the challenges of running in the heat. According to Runner’s World, every 5°F rise in temperature above 60°F can slow your pace by as much as 20 to 30 seconds per mile. Why does this happen? Among other things, all of that sweating we do to cool us down causes us to lose fluids. Our pulmonary system also has to work harder to initiate oxygen flow between the lungs and the muscles. In short, the hotter the temperature, the harder the effort required to maintain our usual pace. What this adds up to is this: during the summer months, you may have to pay more attention to the temperature than anything else. Early morning and later evening runs (when the temperature can be 10-15 degrees cooler) may be your best option. Once things start to cool down, you can go back to focusing on your circadian rhythms.
Most of us have jobs, families, and a host of other responsibilities that can get in the way of getting out the door. While running in the early evening might sync best with our circadian rhythms, it might not sync well with our carpool schedule, homework monitoring, making dinner, and so on.
Although our muscles don’t perform optimally in the early morning, that may be the only time our running group can get in 5 miles together. Yes- there are times when the heat and the flow of our circadian rhythms are worth factoring into our training plan. Despite all the science, the best time of day to run is often just the time that we can manage to fit it into our schedule. And that’s just fine, too!