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Breathing patterns and stride rates

June 28th, 2011

Do you ever find that your breathing locks into sync with your stride when you’re out running? Or with your pedal cadence when you’re cycling? (No points if it happens when you’re swimming.) It happens to most people, but it comes and goes, so there’s been decades of debate about whether it’s a “good” thing, and whether we should try to synchronize breathing with stride. I go into this topic (plug alert) in my new book (pp. 83-85, for the record), but I just noticed a new study in the European Journal of Applied Physiology which adds some interesting insight. It’s a little bit involved, but it’s pretty interesting — so bear with me!

First things first: this was a study (by researchers at UMass-Amherst) of walking, not running — but it’s likely that the same basic processes are at work. Essentially, there are two cyclic systems at work: the “locomotory” system (your legs) and the respiratory system (your lungs). Both are fulfilling separate goals (to keep you moving as efficiently as possible, and to keep your muscles supplied with oxygen), but they also interact with each other — e.g. changing stride can drive greater demand for oxygen. So you’ve got what physicists call a “coupled oscillators” system. The question is: when the two systems are in sync, do they function more efficiently? Do you burn less oxygen at a given pace if your breathing matches your pace?

Here’s what the study did: it had volunteers walk at a natural pace at whatever stride frequency felt natural. Then, keeping the same pace, it had them increase or decrease stride frequency by 10% and 20%, while doing sophisticated monitoring of how closely the breathing rate matched the stride rate, and also monitoring oxygen consumption (a measure of efficiency).

First finding: forcing stride frequency away from its preferred “natural” value made the walkers less efficient. They consumed more oxygen when they either increased or decreased their stride. This is exactly as expected, and has been observed in many previous experiments.

Second finding: changing stride frequency had no effect on how often breathing rates locked in with stride rates — it stayed pretty much the same. Since efficiency changed and synchronization didn’t, this suggests that synchronization doesn’t help (or hurt) your efficiency. Previous studies have found conflicting results for this question, so this is an interesting observation.

But here’s the key finding. The number of different synchronization patterns was greatest at the naturally chosen stride rate. At the lower and higher frequencies, subjects were more likely to lock into their favourite pattern, which was two strides per breath. At the preferred stride frequency — where they were most efficient — they spent a greater proportion of time jumping to different patterns, like 3:1, 4:1, 2.5:1, 4.5:1 and even 7:1. Here’s the data:

So what does this mean?

This would indicate that the greatest variation in the dominant coupling strategy used allowed the participant to explore coupling strategies with the goal of minimizing oxygen consumption.

In other words, we’re efficient at our “natural” stride frequency not because we can breathe in sync with our strides, but (in part) because we don’t let ourselves get locked into one breathing pattern. Instead, we’re unconsciously trying different breathing patterns constantly, finding the one that’s most efficient at that moment and then re-optimizing a  moment later. The moral: don’t try to consciously lock your breathing into a prescribed pattern.

(This doesn’t mean you should never pay any attention to your breathing. It may be, for example, that in stressful race situations you have a habit of breathing shallowly because of nerves. Trying to look out for this and correct it is different from, say, trying to exhale on every second left footstrike.)

  1. Bman
    June 28th, 2011 at 22:00 | #1

    I don’t see any actual coupling of systems here. There are many complicated steps that happen between a breath and when the oxygen reaches the muscles that are contracting at a certain rate. The rate at which oxygen arrives at the muscles is more directly linked to heart rate (which, I admit, might be partially linked to breath rate), and then the process of metabolizing the oxygen begins (which is not, as far as I know, synced in a pattern with breath rate). If there were surges in aerobic energy in sync with breathing patterns then I could accept that there is a coupled system.

    More likely our internal clocks responsible for rhythm just happen to sync breathing with stride.

  2. alex
    June 28th, 2011 at 22:32 | #2

    @Bman
    Here’s what the authors say about coupling:

    “The locomotory system takes care of the mechanical requirements by generating forward motion while maintaining upright stability. The respiratory system maintains adequate ventilation in order to supply the necessary amount of oxygen and to remove metabolic byproducts from the circulatory system. These systems, however, do not act independently of one another. The motor system generates the chemical and neural drive for regulating ventilation and generates mechanical influences directly on the respiratory system. On the other hand, respiration actively contributes to the control of posture, which is cyclically perturbed during locomotion (Hodges and Gandevia 2000).”

    When they talk about “mechanical influences,” you can think, for example, of horses: the jarring force of each footstrike is significant enough that it shakes the horse’s viscera, and FORCES horses to breathe at a 1:1 frequency ratio. Because humans walk upright, they don’t experience the same forces (and most studies suggest that “visceral motion” isn’t a factor in breathing rates for humans), but there may be other mechanical factors that play a role, like limb frequency.

    Incidentally, when you talk about “internal clocks,” that’s a factor that may play a role in why focusing on pumping your arms near the end of a race can keep your legs moving. But that’s another topic!

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