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HrPwr is the relationship between heart rate, and power output. It can evaluate [[Running Economy]] and [[Heart Rate Drift]]. HrPwr is easy to implement, and I have published a [[Connect IQ]] data field called [[HrPwr]] that's available [https://apps.garmin.com/en-US/apps/a105c5df-4900-46d7-bcdb-dbb1b315ff1f here].
=Setup=
You will need a [[Stryd]] footpod to estimate power. You'll also need to pair your Stryd footpod as a power meter. This is in addition to having Stryd paired as a footpod to give speed.
=Background=
My initial approach to measuring [[Running Economy]] outside of a lab was to use heart rate to estimate the effort and distance covered for the effort. This works okay on the flat, as distance covered is a good measure of effort. However, as anyone who has run hills knows, slope dramatically change effort. The [[Stryd]] footpod estimates the power output based on pace and elevation changes, which solves this problem nicely. It also gives the possibility of comparing data from running with cycling, though I've found the Stryd power estimate to be much higher for a given perceived effort than cycling.
There are three uses for HrPwr.
# During a run, you can use HrPwr to see [[Heart Rate Drift]]. I see this during my long runs, and I can use HrPwr to test how effective my hydration, fueling, and cooling approaches are.
# On a day-to-day basis, HrPwr can detect possible health and fitness issues. I've found that [[Glycogen]] depletion can cause a lower HrPwr in the early stages of a run, as can heat stress. Likewise, my HrPwr is lower at the start of a race because of increased stress, though it settles down as I relax into things. Lower HrPwr sometime shows I'm more fatigued than I realize.
# Over the long term, HrPwr should rise as you become fitter and have better [[Running Economy]]. Some of the increase in HrPwr can come from Running Economy directly, but it can also be due to improved cardiovascular fitness that delivers more oxygen per heartbeat.
[[File:HrPwr HR Drift.jpg|center|thumb|300px|My HrPwr over the course of during a long run. You can see the gradual decline in HrPwr as I become dehydrated and [[Glycogen]] depleted.]]
=Formula=
The formula I use is below and is the power output in milliwatts per Kg per heartbeat.