There is an alternative measure that is more subjective called the Perceived Rate of Exertion (PRE).
For me it’s a scale that coincidentally equates pretty closely to my heart rate: 100 + (PRE x 10).
Thus I’ll warm-up at a PRE of 2 – 3 and then do an aerobic run at a PRE of 3 – 5.
If I’m running at a heart rate of 150 then I find I can talk but it’s not conversational. So I treat this as a limit. To go faster means I’m leaving the aerobic zone and climbing into the anaerobic zone.
Keep in mind that your heart rate is affected by hills, heat and humidity – and the subsequent dehydration that can occur – as well as altitude.
It’s a simple way of ensuring that those runs that should be easy to moderate don’t end up being too hard.
Kim | marathon runner