I thought I'd mention a little thing I've been doing.
During my daily riding (commute, errands) I ride the biggest gear I can push. I mean, at some sort of low but still reasonable cadence. For around town, this usually means 53 x 17 or 15. When the road turns up, I go up the cogs, but stay in the big chainring. I'm trying to not use my 42 at all, except when there is no choice. Whenever I get into an easy rhythm, I drop a cog until it is hard. I don't let myself stand, unless I have to get out of a car's way or something.
The goal is to use routine rides to get stronger. Most of us ride enough that around-town riding isn't that much exercise. But if we deliberately make it hard on ourselves, we can get more out of those otherwise short and unchallenging rides.
(A couple years ago, I decided my standing pedaling was weak. By making myself pedal for long-ish periods standing, I improved a fair bit.)
One thing I've noticed is there seem to be two ways to pedal when you're pushing a too-big gear. Either I slide forward to the rivet, or I push myself to the rear of the saddle. I think the latter works better because there is more glute involved, and the extra leg extension allows a simultaneous push and pull by opposite legs. The rivet position seems to exhaust my quads.
Do you intentionally make routine rides harder, or otherwise find a way to get more exercise value from them?