Can't increase MHR? I'm not sure about that and would appreciate links that show that. As you get more fit you ...get more fit...your heart gets stronger. A year ago when I went all-out to the point of breathing very very rapidly and being ready to collapse I would hit 161. Last week I was able to push up to 172. Previously I could simply not make my heart go any faster and that has to pretty much be the definition of MHR. For a 55yr old person to hit 186...that's impressive and a resting HR of 52 shows he is really good shape. I venture to say if he became a couch potato for a year his MHR would drop considerably. I can sustain 144-148. I can go for a while above that but not sustain it. When I started working out a year ago I was topped out around 135 and couldn't hold 145 for any length at all. Time on the bike and attention to your breathing vs. heart rate will tell you what you need to know over time.