78. I had a noticeable drop-off at 63 and again at 70, no idea why really. Might have been that I'd eased off for a short period and then couldn't get it back.
So 2 things: never quit but OTOH, cut back on the quantity of intensity. The commonest things to happen are the advent of aFib or vTach, then doctors. Both those are a result of too much top end work and can be game changers. Read through the Pills and Ills subforum.
Another thing is sarcopenia. Consistent work in the gym is the solution to that. Strength does not seem to be as age sensitive as is aerobic ability.
Personally, I prefer lower gears to going electric, although the association between going electric and loss of cycling strength seems to be individual. Some folks just push the button, others don't until they hit their redline. It's just too easy to avoid a little pain.
My wife and I have been riding a tandem since '07. I seldom ride my singles on the road any more, the tandem is just too much fun. We've toured on it, really fun.
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