Bike & Stairs...

Today I rode for 7 miles at park I have never biked at before & I also climbed the stairs, walked & jogged for 1 hour at the high school.  Total calories burned was 842.  I had a maximum heart rate of 170 on the stairs, but that doesn't seem possible, especially since my avg HR for the hour was only 126!  I don't remember being so completely out of breath as I have on some of my bike rides!  Very strange anomaly!