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A Cruise Control for Running

An app that tweaks the beat of your music controls your pace by altering your cadence.

Media Platforms Design Team
I have to admit, the idea of a "cruise control" for running sounded pretty silly to me when I first heard about it. But consider me a convert, in theory at least. If you haven't heard, there's a new app for iPhones called Cruise Control: Run. It does just what you'd expect: you enter in the pace you want to run at (e.g. 8:15 per mile), and it will enable you to stay at precisely that pace, as I described in my Globe and Mail column this week:

It controls your pace by subtly increasing or decreasing the speed of the music you’re listening to, while monitoring your speed with the built-in GPS and accelerometers in the iPhone, according to Max Donelan, a professor of biomechanics and neurophysiology who developed the technique with PhD candidate Mark Snaterse.

As long as you keep your footsteps in time with the beat of the music – a synchronization that happens almost automatically – you’ll speed up and slow down on cue, without even realizing it. With this technique, the app can keep you locked to within about 1 per cent of whatever goal pace you’ve programmed in, Donelan says.

The app also works in other modes -- e.g. in Free Run, you just run at whatever pace you want, and the app will make sure that your music synchs to your stride automatically. Or if you're into running at a specific cadence, you just plug in, say, 180 strides per minute, and your music will adjust to keep you at that cadence.

Speaking of cadence... the only reason that the cruise control app works is because we each have a unique relationship between preferred speed and cadence. If I ask you to run at a certain speed (by putting you on a treadmill, for example), you'll naturally settle into a preferred cadence for that speed. If I speed the treadmill up, you'll speed up by lengthening your stride and increasing your cadence. I asked Donelan if he'd ever encountered anyone who sped up exclusively by lengthening stride while keeping cadence constant, and he said no -- this is pretty much universal behavior. Decades of studies have shown this to be true, which is one of the reasons I don't believe that runners should aspire to run at a specific cadence like 180 steps per minute: the right cadence for your body depends on how fast you're running.

Anyway, the cruise control function does the same thing but in the opposite direction: it sets a cadence, and you respond by speeding up or slowing down. Of course, the relationship between speed and cadence may change as you get fatigued, or if you're on hilly or rough terrain. That's why the cruise control is a "live" app that constantly measures speed in real time. It doesn't just assume that cadence 182 corresponds to 6:45 miles or whatever.

So why am I such a fan of this app -- even though I don't even have an iPhone? It's because it comes from years of serious research at a top biomechanics lab (the Locomotion Lab at Simon Fraser University). The cruise control idea came from trying to answer a simple question: how does your body know what the "optimal" stride parameters are to minimize energy consumption at any given pace? Over the years, studies have found that humans are very good at picking a "natural" stride to minimize energy consumption. If you force them to run with shorter steps, or faster cadence, or higher bounce, or whatever tweak you can think of, they tend to burn more energy. (Note: this is for short-term changes only -- that doesn't mean that you can't develop a more efficient stride by making changes over the long term.)

So Donelan and his colleagues have been testing various hypotheses about how the body "knows" how to be efficient. They've built a system where they can control the oxygen and carbon dioxide levels in their subjects' blood independent of how hard they're running, to see whether we adjust stride based on those metabolic markers. They're also building a virtual reality system that can distort the visual flow passing by (e.g. making it seem like the scenery is going past a little quicker than normal), to see if that can trick your body's effort-sensing mechanisms. In short, they're really thinking carefully about what it means to play around with parameters like stride length and cadence. The app is a cool spin-off, but I'm just as interested to see the results of these other experiments when they're published.

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