Cardiac Drift

Happy 100th Article

“Cardiac Drift” - A very scary term that sounds like it’s some kind of terminal disease or consequential health event. Do not fear. It’s a simple over-arching phrase that affects all endurance athletes.

Simply put, it’s the phenomenon of your heart rate rising over time, as your pace (and relative effort at time) stays constant.

A very simply chart displaying this: (I’ve shown this chart before, but I haven’t broken down all the components yet.)

This chart is an exaggeration of what it actually looks like in the real world. But it usually it looks something like this—where you second mile HR is about 20BPM lower than your ending HR at the same pace.:

But how can we make it so your chart looks flat, and less “drifty” towards the back half?

The answer is nuanced in dealing with cardiac drift. Many factors are in play that you might not be aware about, that change day-to-day. There are also different ways to actually measure cardiac drift, with different levers to pull in combatting it.

First you need to understand the physiological process’ that cause cardiac drift. Why does the heart need to pump more over time, to achieve the same pace?