Originally Posted by
tomato coupe
I would say the old rule of thumb doesn't work for you, since 220 – 61 = 159, which is significantly lower than 173.
I'm 62, and my theoretical max of 158 bpm is well within a sustainable range where I can converse with fellow cyclists and ride for an extended period. I was recently tested at 171 bpm in a hospital lab, and though I was significantly winded, I can only guess that my max was possibly 5-10 bpm more. But what is max anyway? A fuzzy line of exhaustion?