Think Fast

Yes, you need to train your legs, but it's really your brain that dictates your pace.

September 5, 2008

If you're like most runners, you discovered the importance of pacing the hard way. You started too fast in your very first run or race, and ended up staggering and wheezing through the second half. But you learned your lesson and held back on your next attempt, allowing you to make it to the finish without the urge to vomit. Eventually, however, you may face a new dilemma: You become so good at running conservatively that you finish feeling too comfortable.

Perfecting your pacing-trying to run a certain distance in the shortest amount of time possible without falling apart-is a tricky art. That's because even when we watch the clock, we run largely by feel: We decide whether to speed up, slow down, or hold steady based on how much discomfort we think we can handle.

Until recently, exercise science gave little attention to this mental side of pacing. If you petered out midway through a run, most experts would say your body temperature got too high or there was too much lactate (a fatigue-producing chemical) circulating in your blood. But Ross Tucker, Ph.D., an exercise physiologist at the University of Cape Town, South Africa, and a growing group of exercise scientists believe there is a more complex system at work. Their research shows that your brain reads what's going on in your organs, tissues, and cells while you're running, and then uses that information to get into the right rhythm at the start of a run and then fine-tune your pace as you go. Learning how these internal sensors work is the key to becoming a better pacer and stronger runner.

The Science of Pacing

Exercise scientists were turned on to the idea that your brain controls pace by a German researcher. In 1996, H.V. Ulmer theorized that when you perform a task, your brain focuses on the endpoint (a finish line; when the treadmill clock hits 30 minutes), and it works backward from there, calculating how hard you can push yourself and still complete your workout. Several years ago, Tucker and his colleagues, including renowned exercise physiologist Timothy Noakes, Ph.D., started conducting experiments on Ulmer's theory, which they now call "anticipatory regulation," meaning your brain anticipates when you're going to be done running and regulates your pace accordingly. "The brain controls exercise performance to protect the body from reaching a failure point or a potentially harmful level," Tucker says.

How does your brain know this limit? "The brain receives signals from the body and interprets these signals in the context of the exercise bout," Tucker says. So your brain reads the exercise intensity and checks in with all the various systems in your body (Do you have enough fuel? Are you well-hydrated? What's your body temperature?) to determine if you can keep up that pace and still finish. "Then the brain changes the degree of muscle activation to slow the athlete down or allow him to speed up," Tucker says.