Pacemakers are not a big deal, for the most part. The typical pacemaker that only cuts in when the HR drops to a set value, does not represent any additional risk to a person. They can go wide open and need not worry. A de-fib pacemaker may present some small amount of risk, although one of the fastest cyclists in our area has one and it doesn't hold him back at all. I guess any additional concerns or risks would be tied more to any heart conditions or anomalies, not so much the pacemaker.

Technically no, MHR cannot increase with age. However the ability to generate a higher HR through greater exertion is certainly possible. That's just one of the many reasons that folks who train with HR ignore MHR and use LTHR instead. Ignore it except as a measure of how hard you're working.

This thread or section should be for 60 years old or more--because 50 is incredibly young enjoy your youth!

My guess is that some of us, as we become more experienced and faster, become more comfortable in the pain cave and our minds let our bodies push harder. I agree that max HR is in the "cool but useless" info category.

My HR during a 20km TT is in the 160-162 ballpark. Doing 20' threshold intervals it gets into the low 150s. At my normal cruising speed, it's in the low 120s. That last part used to be in the 130s and decreased as I've gotten fitter.

Strava Premium puts a "suffer score" on each ride, which is a weighted linear combination of time spent in various HR zones. I've been off and on the bike over recent years, now back on. Over the past couple of rides I have noticed a big uptick in my suffer scores. Physically I feel the same, but I notice that my HR is running hotter, about 10 bpm, on the average, and it shows in the suffer score. For example, I went out today for 40-ish miles with maybe 1800 feet of climbing. I've done this ride a few times; here's a couple efforts for comparison:

Early April
Suffer Score: 114
Avg. speed: 14.7 mph, 2:42 moving time
% in Z3 (143 bpm to 161 bpm): 78%
% in Z4 (162 bpm to 178 bpm): 2%

Today
Suffer Score: 165
Avg. speed: 14.7 mph, 2:39 moving time
% in Z3 (143 bpm to 161 bpm): 54%
% in Z4 (162 bpm to 178 bpm): 35%

I asked my doctor, so I'm not just relying on BF wisdom, but I am still waiting for the reply. This month, so far, I'm at a little over 200 miles total, about 9,200 feet of climbing. Nothing extraordinary. But I'm wondering how much fitness-- not age-- can help increase lactose threshold, heart rate, and so on.

At this time of year, I don't have the legs to push my HR up above about 145. Just about the time I am starting to breathe deeply, my legs burn out and I have to back off. Later in the year, the situation will reverse and I'll be able to max out my HR and still have legs left.