Ten years ago, I did a couple Conconi treadmill runs to exhaustion. My HR maxed at 188. I recently re-started run/walking for 5k three times a week. For the first month, my running heart rate topped out at 178-179. In my fourth month, it is topping out at 170-174 for the same perceived exertion. As I get more fit, it seems like my HRmax is coming down? Really?