I freakin love this!
As my many Strava followers know, I have started wearing my forearm HRM on outdoor rides and I had no idea it was so easy to estimate training load/stress from the mean HR data. Free software will look back at your rides workouts with HR AND power, model the relationship and give you a load estimate based on it. The best part, though, is how pretty the relationship is. I love me some big R value. While this obviously doesn't replace a power meter, it does do one of its important functions.
