The short answer is late afternoon—unless you normally run at some other time.
A couple weeks ago I rolled out of bed on an uneventful Thursday morning and went for an easy 6-mile run from my apartment. I covered my usual out-and-back route in 45 minutes, which seems to be par for the course when I lace up the sneaks before 10 AM on a weekday. Four days later, at 5 PM on Monday, I ran the exact same route at an equally easy effort and the watch read a few ticks over 42 minutes.
It was nearly a 3-minute improvement over the same course in similar conditions just a few days later, with the only discernible difference being the time of day I headed out for my run. Afterward, I stood there for a second wondering, “Did my fitness really improve that much over the weekend or are my workouts simply more effective later in the day?”
Of course, it’s highly unlikely that I became 7 percent fitter in just four days – especially since I haven’t been doing anything in the way of hard workouts lately – but there is probable cause and research to show that running later in the day may very well contribute to improved performance.
Looking back to the morning I hit the roads roughly half an hour after waking up, the most salient thing I remember was how long it took me to get going. Initially I couldn’t move much faster than a crawl, but by 2 miles into the run I had seemingly woken up and established some sort of rhythm. When I headed out on the same route a few days later, however, I found my stride almost immediately and was amazed by the ease of my effort and how much life I had in my legs. It was like night and day, no pun intended.
Aside from my own observations, a March 2009 article published in the New York Times says that various studies by scientists have shown that athletes tend to perform better in workouts that occur between the hours of 4 and 8 PM, which is when body temperature and performance-relevant hormones are at optimal levels to support exertion. One of those studies, conducted in the Department of Kinesiology at the College of William and Mary in Virginia, concluded that, “the data demonstrated significant chronobiological oscillation in peak torque, average power, maximal work in a single repetition, and total work per set…these data suggest that maximal muscle performance does vary within the segment of the day when exercise typically occurs.”
What does this mean? Quite simply, time of day does have some effect on power and performance. In most cases, the more time you give your body to warm up and get loose, the better it will run. In this respect your body is like a car parked outdoors. When you go to start it up first thing on a cool morning, you might have a hard time turning the engine over, and once you finally do, it putters down the street for a bit until the internal temperature reaches an optimal level. Later in the day, however, you’ll notice the same car starts up a lot quicker and runs more efficiently than it did earlier in the day. The human body works in much the same way.
For many people, however, life doesn’t always allow for late-morning, afternoon or evening workouts. Sometimes it just has to get done first thing in the morning, and fortunately for you early risers there is research that shows a correlation between circadian rhythms and the time of day during which someone works out. A 1989 study on “Circadian Specificity in Exercise Training” by Hill, Curetan and Collins concluded that “subjects who trained in the morning had relatively higher post-training thresholds in the morning, while subjects who trained in the afternoon had relatively higher values in the afternoon (p less than 0.05). This is evidence of circadian specificity in training and supports the notion of planning physical preparation to coincide with the time of day at which one’s critical performance is scheduled.”
So whether you’re an early bird or a night owl, your workouts are going to be most effective at your habitual workout time. While muscles are certainly stiffer and energy levels are lower first thing in the morning, if that’s when you’re used to running then it’s worth sticking to your schedule and allowing your body to maintain its regular rhythm. But if you’re looking for enhanced energy levels and want to get going a little faster than you ordinarily would, try running a little later in the day if possible. Remember, a little variety never hurt anyone.
So, what time will I run tomorrow? The answer is easy: whenever I can find the time!