Inside Triathlon Archives: The Perfect Day

  • By Matt Fitzgerald
  • Published May 24, 2013
  • Updated Nov 6, 2013 at 12:52 AM UTC

New research on the circadian rhythm tells us when to eat, sleep and train—and how this can help us race faster than ever.

The following story was published in the September/October, 2011 issue of Inside Triathlon magazine.

It is said that our bodies have clocks—body clocks. It might be truer to say our bodies are clocks. Recent advances in the understanding of the circadian rhythm, the 24-hour cycle of sleep and wakefulness and related processes, have revealed that the functioning of our bodies is affected far more extensively by circadian rhythm than was previously known. We now know that one out of every 10 genes in human DNA operates in 24-hour cycles.

In practical terms, what this new knowledge is telling us is that our bodies really want us to do certain things at certain times, namely sleep, wake, eat, be active and rest. When our behavior defies the programmed preferences of our body clocks, our bodies do not function as well as they should. If we sleep too little or too much, or if we eat when we shouldn’t or don’t eat when we should, our health is compromised. Our metabolic systems seem to be most affected when our lifestyle gets out of sync with our circadian rhythm. People who are chronically sleep deprived, for example, are more likely to become overweight or diabetic. And for athletes there are additional consequences.

“One of the problems that athletes have is that their lifestyle is fighting what their normal circadian rhythm is,” says Robert Portman, Ph.D., co-author of a new book, “Hardwired for Fitness,” which presents a diet and exercise program based on aligning behavior with circadian rhythm. “When that happens, you create metabolic inefficiencies.” For example, the athlete’s muscles might lose some of their ability to burn carbohydrates, which is critical to performance in workouts and races.

Circadian science suggests there is a right time for a triathlete to do everything. A triathlete who does everything at the right times over a 24-hour period has lived what we might call a perfect day. And a triathlete who lives a perfect day every day will realize his or her full potential in races. Of course, not enough is known to rigorously define a triathlete’s perfect day, and even if we knew everything, it would still be impossible for anyone to be perfect every day. Nevertheless, it’s a worthwhile exercise to define a perfect day in general terms.

When to Exercise

Some people—whether by choice or by necessity—are morning exercisers. Others are afternoon or evening exercisers. Of course, many triathletes are both. When is the best time to exercise?

Studies have shown that most people perform better and also feel more comfortable when they exercise in the afternoon. For example, in a 2009 study, French researchers recruited 16 competitive cyclists and had them perform a high-intensity exercise test at both 6 a.m. and 6 p.m. The test consisted of a maximal one-minute effort on a stationary bike against resistance. Researchers measured the cyclists’ peak power output, their mean power output for the first 30 seconds of the test, and their mean power output for the full minute. On average, the subjects performed roughly 8 percent better in each of these metrics in the afternoon than in the morning. But why?

“Our body temperature is lowest when we wake up in the morning,” says Portman. “Then it increases until about 2 or 3 in the afternoon. That’s the high point of the day. There’s been a fair amount of research done with endurance athletes and resistance athletes which shows that performance does improve when you exercise when your body temperature is peaking.”

That settles it. If you work out once a day, you should do it in the afternoon, when you can perform better and, by performing better, get a bigger fitness-boosting stimulus from the work. Right?

Not so fast. Other research has shown that exercise performance improves most at the specific time of day when workouts are habitually performed. So, if you always work out in the afternoon, your afternoon exercise performance will increase more than your morning workout performance. And if you always work out in the morning, your morning workout performance will improve more than your afternoon workout performance. For example, in a 1998 study, researchers at the University of North Texas put a group of college-age female non-athletes through a five-week high-intensity cycling interval training program. Half of the women did all of their workouts in the morning. The rest did theirs in the afternoon. At the end of five weeks, all of the subjects performed two separate high-intensity rides to exhaustion, one in the morning and one in the afternoon. The morning exercisers performed significantly better in the morning test, while the afternoon exercisers put up much better numbers in the afternoon test.

When do most triathlons take place? Early in the morning. Therefore, even if you are an afternoon exerciser by habit, you’ll want to consistently do some workouts in the early morning so that your race performances aren’t compromised by a lack of specific physiological adaptation to exercising at that time of day.

So, where does this leave us? If triathlon is one of the most important things in your life and you have the time, habitually exercising twice a day most days is your best bet. Not only will you become fitter than you would on a once-a-day training regimen by virtue of greater training volume, but you will enjoy the benefits of being able to work harder in your afternoon workouts and the specific improvements in morning exercise performance that come with training in the morning.

If you cannot or prefer not to exercise twice a day most days, then you’ll want to be sure to routinely do some of your workouts in the morning. If you’re normally a morning exerciser, go ahead and do all of them in the morning. If you’re normally an afternoon exerciser, breaking from that habit once or twice a week should be enough to avoid putting yourself at a disadvantage in morning races.

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