|Getting Into Your Exercise Groove|
This isn’t meant as an insult, but you are physiologically lazy. So am I. So are we all. Using treadmill testing, scientists have definitively established that, like other animals, humans naturally aim to use as little energy as possible during most movement. So when we walk or run, our bodies tend to choose a particular cadence, a combination of step length and step frequency, that allows us to move at any given speed with as little physiological effort as possible.
How we pick that cadence, though, and whether we can or would even want to change it has been unclear. But a series of recent studies involving runners, walkers, metronomes and virtual reality curtains suggests that while the tug of physiological laziness is strong, it can be controlled, or at least tweaked, with some conscious effort — and perhaps your iPhone playlist.
In the first and most revelatory of the studies, physiologists at Simon Fraser University in British Columbia asked adult volunteers to walk on a treadmill at an easy pace. Using motion capture technology, the scientists determined how many steps each person was taking per minute at this speed. A person’s pace depends, of course, on both step length and step frequency. But because the two are inextricably entwined — lengthen your stride and you’ll take fewer steps over a given distance — studying one provides sufficient information about the other, and frequency is easier to enumerate.
After establishing each volunteer’s preferred step frequency, the scientists then sped up or slowed the treadmill, and the researchers measured how quickly people’s legs responded.
The body, remember, wants things to be easy. When you increase or decrease the speed of your walking or running, various physiological changes occur; the amount of oxygen in your blood rises or falls, for instance, because your muscles start requiring more or less of the stuff. Other biochemical changes also occur within muscle cells. Sensing those changes, the body realizes that, at this new speed, your cadence isn’t ideal; you’re taking too few or too many steps to use the least possible amount of energy. Your body adjusts.
But that process takes a little while, at least five seconds or so for the oxygen levels to change and your body to recognize the alteration, says Max Donelan, a professor at Simon Fraser University who was a co-author of the study with his graduate student Mark Snaterse and others.
However, the walkers in the study were adjusting their step frequency within less than two seconds after the treadmill speed changed, Dr. Donelan points out. They then fine-tuned their pacing after that. But the first adjustment came almost instantly.