Those indoor long climbs - how long?

The strongest I ever got, I was doing 3 sets of 30 with increasing weights, the last set only able to do maybe 27 reps, full depth, ass to grass squats. I was doing circuit training, so it was a few minutes between sets. Plus sometimes an hour of Z2 or Z3 on the step mill - "the stairway to hell." Gym twice a week. Plus of course long competitive group rides. Early 60s. Increased efficiency translates as more power, period. One has a tendency to go by HR really, not power, it's more about breathing which is tied to HR. That's assuming that one is giving everything one can. One tries to get power up at specific breathing rates. Which is of course efficiency, or at least one can call it that. Most studies find that gym work increases endurance, which translates as less HR drift. I don't really know anything about the mechanism, just that it works.