I push myself on some climbs and small hills. Yesterday I hit 184 BPM and 668 Watts. I occasionally do a sprint, when I think about it, but it is not a regular deal since I don’t think about it. About a year and a half ago, I pushed myself on a 2 mile climb and the next day started having some unusual heart rhythms. Ended up at the ER and then immediately moved into the CCICU. It was determined after too many tests to count, I had bigeminy (an extra beat), which resolved itself in a few weeks - but understand it can return. As a result, I don’t push myself on long efforts, but certainly enjoy pushing hard on short punchy efforts. BTW, I am 70 and still enjoy getting after it as well as keeping my average speed up.