If you’ve ever felt as if the treadmill seems to be going uphill in the morning and downhill in the evening, or that you run noticeably faster after work than at lunchtime, don’t worry—you’re not alone. In 30 interviews with runners, from average club plodders to Commonwealth Games 1500m champion Michael East, every one claimed to run better at one time of day than another. Many had even put this to the test.
For example, Andrew Grace, a 2:53 marathoner from London, had to do the majority of his running early in the morning because of work. On Wednesday, however, he was able to leave work a little earlier, so he trained in the evening, which always felt easier. He put it to the test and found he was consistently at least a minute quicker over the same seven-mile course without expending any extra effort. "If anything, the evening run seemed easier, even though I was going faster," he said.
Many of the runners thought the reasons for this change were psychological. "I just feel better when I’ve got work out of the way," and, "I always feel miserable in the mornings," were common reasons. Others blamed poor sleep or even the previous night’s meal! According to a significant branch of science, however, a more likely explanation is a perfectly natural phenomenon known as circadian rhythms. These are small fluctuations in the performance of bodily functions on a 24-hour basis. "Practically every bodily function shows daily rhythmicity," said Dr. Roberto Refinetti, Chief Editor of the Journal of Circadian Rhythms. "So that means, in theory at least, you can improve your ability to do something simply by selecting the right time of day to do it." In total we have more than 100 different circadian rhythms controlled by the suprachiasmatic nucleus, a biological clock in a part of the brain called the hypothalamus. Although scientists have yet to pinpoint the exact mechanism it uses to pace your body, they know that daylight, social contact, and meal times are all factors.
The important thing, from a running perspective, is that many of the functions vital to putting in a good performance peak at the same time. For example, one of our daily fluctuations is in body temperature. Scientists have found that body temperature is at its lowest in the early hours of the morning and peaks in mid- to late-afternoon. It has also been shown that athletes perform better when body temperature is higher, which is perhaps why Grace found it so much easier to run in the evening. A new study also suggests our lungs work best at this time too. To analyze which time of day is right for you, here’s a quick survey of the specific positives and negatives of running at different times.