Ah ha. This is a new one. This was a bit complicated to set up on my Garmin, but fun to do. I had to start out with my heart rate at 80% of threshold (which is 160 bpm) and increase by 5 bpm every 5 minutes until my heart rate was at 100% of threshold. Once there, drop back down to 80% and do it over again.
It was hard to run slow enough to stay at 80% of threshold but it got harder at the end when I was overheated. I really need to figure out this heat thing. Before my race on Thursday, I am going to drink ice water to see if that helps keep me cool a bit longer. Anyone have any tips?