What you listen to when you jog matters

Mar 19

A few weeks ago, my wife mentioned reading an article about running and music tempo. I don’t remember the details, but she said that the article asserted that most long-distance (maraton or longer) runners seem to run at roughly 180 strides per minute. Presuming that their music would be pretty close to their stride rate, one can assume that their iPods are chock full off 180 bpm tunes.

Have you ever listened to 180 bpm music? It’s scary stuff.

Seriously though. I got to thinking about the effect of BPM on work. It makes sense, but it’s a little counter-intuitive: the faster the BPM, the less work you do when you run. I know. It sounds crazy. But let me explain.

It turns out that the majority of work that you’re doing when you run is not actually pushing yourself forward — it’s fighting off gravity. Think about pushing off of the wall at an ice skating rink: you can get pretty far on much less energy than it would take you to actually walk the same distance.

With each stride, you bounce upwards a bit. And technically, even if you don’t feel like you are all that bouncy, your center of gravity is bouncy and the work is still being done. The height of that bounce is related to the length of your stride, which is in turn related to your speed and your BPM (strides per minute):

  1. Given a constant speed, the more strides per minute you take, the shorter each stride will be.
  2. The shorter the stride, the less you bounce.
  3. The less you bounce, the less energy you expend fighting gravity.
  4. Thus: faster BPM equals less work.

Long story short: if you’re running to lose weight, slow down your music but keep the same speed (pace). If you’re running for distance, crank up the BPM.

Update: Hey! You! Yes, you! DO NOT take this to mean that you can crank down the BPMs to something ridiculous just to lose weight. You will destroy your knees and ankles that way. I’m just saying that if you want to lose weight, keep the BPMs at a comfortable pace and don’t crank them up.

I’ve written a quick Flex application called Prancer that shows this interactively. Punch in your weight, a target distance and time, and your BPM, and it will generate an estimate of how many calories you will burn. The graph will show you how the BPM affects the total calorie burn. Some less-interesting metrics derived from the numbers are shown below.

Oh, and it’s called Prancer because my wife says I bound like an reindeer when I’m trying to run her speed. There was also something about being a Pretty Pony, but we’re not going to go there.