Entrainment of Locomotion and Breathing
One particularly intriguing observation that may have bearing on the organization of intrinsic clocks is that stride rhythm is often coupled with breathing during locomotion. That is, for a certain number of strides, there is a breath. This is called entrainment of ventilation and locomotion, and it has been observed in cats, dogs, horses, jackrabbits, gerbils, rhinoceroses, wallabies, turtles, guinea fowl, alligators—pretty much the whole ark.
Given this evidence for the evolutionary persistence of entrainment in the animal kingdom, it is no surprise that the phenomenon is also observed in humans who are running, walking, cycling, or rowing. In human studies, the reported frequency of the link between breathing and striding has varied widely. (In fact, some have found no evidence of entrainment at all.) Perhaps insightful, though, are the observations of Dennis Bramble and David Carrier at the University of Utah that the frequency of entrainment depends on the performance level of the runner. Experienced runners commonly coupled stride and breathing patterns very tightly. The most common ratio was a 2:1 ratio of strides and breaths, but at slow running speeds, this was frequently 4:1. However, in less talented runners, no synchronization of breathing and striding was observed at all. (So, here’s another laboratory exercise to try. Check yourself for breathing-striding entrainment during your next run and see which category you’re in.)
The explanations for the link between breathing and striding during locomotion have generally involved mechanical issues. Gait, for instance, may physically constrain breathing, thus requiring the two to be synchronized. However, such mechanisms would seem to be less likely linked during the upright bipedal locomotion of human beings. Alternatively, a combination of effects of a single internal clock that links the two different forms of rhythmic activity is an intriguing possibility.
Does entrainment help performance? It depends, it seems, on which expert you talk to. Jack Daniels, who was introduced earlier in this chapter, thinks so. Given his extensive experience as an athlete (U.S. national titlist in the modern pentathlon), coach (University of Texas, SUNY at Cortland), and exercise physiologist (University of Wisconsin), he’s somebody who should know. He notes that the best runners use a 2-2 rhythm, taking two steps (one with each foot) during inhalation and two steps during exhalation. If you’re striding at Daniel’s proffered rate (90 steps with each foot per minute), you’ll then be taking around 45 breaths per minute. He believes this provides the most efficient ventilation of the lungs.
So, according to his renowned book Daniels’ Running Formula, a 2-2 rhythm is preferred for the majority of a distance race. However, near the finish, you will probably want to breath faster, around 60 breaths per minute. Then you can switch to a 1-2 rhythm (take one step while breathing in and two while breathing out), or 2-1. Slower rhythms, such as 3-3 and 4-4, might be okay for easy training runs. Daniels says to avoid a 1-1 pattern because the shallow breaths decrease actual lung air exchange.
Jerry Dempsey is to respiratory exercise physiology as Jack Daniels is to distance running coaching. And Dr. Dempsey disagrees. “My argument, purely theoretical, is as follows. We have shown that the oxygen cost of breathing at maximal exercise in highly trained athletes can comprise as much as 15% of the total oxygen demand. This means a fair bit of blood flow is being required by respiratory muscles that is potentially stolen from locomotor muscles. So we need our breathing to be as mechanically efficient as possible. To me, the mechanisms in the brain stem are best designed to receive all of the input from the lung, chest wall, cerebellum, and hypothalamus in order to sculpt the optimal depth and rate of each breath to minimize the work of respiratory muscles. Higher centers, including the cortex, willing our breathing pattern to coordinate with limb movement would not provide the same level of optimization. So, in essence, I believe the brain stem of the runner is better equipped than the cerebral cortex of a coach to determine breathing pattern.”
Distance runners Paul Norton and Jack Mahurin, whom you met in the previous chapter, line up with Professor Dempsey on this one. They both told me that anything that departs from just doing what comes naturally with your breathing is counterproductive. They think that concentrating on creating a certain pattern of breathing and striding wastes mental effort.
So, it comes right back to chapter 1’s argument of the subconscious central governor versus our own conscious dictates, doesn’t it? Should we let Mother Nature, with centuries of evolutionary practice, have her way? Or can we consciously adopt certain running (or in this case, running and breathing) strategies that will improve performance? I guess if people like Professors Dempsey and Daniels can’t agree, we can safely call the answer inconclusive. But there may be a takeaway suggestion, too: Runners can try out active entrainment to see if it works.