Hills with Travis

I was dressed for a slow easy run. I was going to work on my form - less heel strike, more ball of foot. And then Travis (#2 son, 17) comes in from working out and is going for a run. Dad ask meekly, "can I run with you?" Travis, "sure, but I am running the hills".
So off to the hills we go. Short sprints up a steep grass hill at the high school. He goes up 10 times, I go up 8 times. Travis, "let's move to the STEEPER hill and do 5 more". Dad's lungs say, "no"; dad's heart says "no"; dad's mouth says, "yes". Then we move to the steeper hill. We both go 5 times. Short intense workout. Time well spent with Travis.
No heart monitor which was good because I am sure that I really did not want to see my heart rate.