Treadmill grade

I ran/walked 9 miles yesterday. I ran/walked 12 miles today. I ran the first part of my 12 miles today, but I just really didn’t have the energy to run today. So I started walking. When I walked, my heart rate would drop. I would occasionally run, and my heart rate would come back up. Then I got an idea. I cranked the grade up to 4.5%. I was walking at that grade at 4.5-4.6mph. It was definatly using different muscles. I took a short break to do some stuff on the computer. Then I got back on the treadmill. I cranked the grade all the way up to 10%! Wow! I had to drop the speed down to 4mph to stay in the proper heart rate zone. When I got up to 11 miles, I dropped the incline back down to 1%. WOW! It felt like I was walking downhill! I raised the speed up, and only upto 4.3 mph since I wanted to cool down a little. Following my workout, I could feel it in my legs. I climbed into a hot bath tub and soaked for a while. I will have to do this workout again. It will be usefull when I am running the Damn Wakely Dam Ultra which will be in the Adirondack mountains with a lot of hills!