How HR Works

I just read this from Alan Couzen's blog. There is no mystery here - the harder you work, the more O2 your muscles need, the more your HR beats to deliver the O2 to your muscles.

Here is how you calculate required HR given a certain work rate:

Say you are riding your bike at a certain wattage that requires 3.5 Liters of O2 per minute. What will your HR be?

You need to know a few things about your physiology that most of us don't unless you've had blood work or anaerobic testing done, but if you did know, here is how you'd calculate it.

If you have 12g of hemoglobin per deciliter of blood, this deciliter would carry 160ml of O2 per liter of blood (assumes avg hemoglobin per deciliter and 100% blood saturation).

If your muscles require 3.5 liters of O2, you would need to pump 22 liters of blood per minute (3,500/160).

If you assume a cardiac stroke volume of 150ml, it will take 150 beats per minute to deliver 22 liters of blood to the muscle.

HR to push the certain wattage? 150 bpm.