I first got into power training with a Mavic Max (which no one knew how to use and you couldn’t manage the data), then a Computrainer in '94, then on-bike PMs from '98 to now (with w few PM-less years sprinkled in between). For most of those years, the focus was on w/kg.
When I passed 50 two years ago, I decided to do something about my upper body, and have done a lot more strength training and time on the rowing erg.
The result is total power is up, but watt/kg is down, due to carry 4 more kilos of mass from the weight I kept myself at during my 20s-40s (72kg).
At this stage, I’m ok with that. I’m more concerned with overall heath and maintaining muscle mass as I get towards 60 than with watt/kg (which peaked long ago).
I’m curious about the perspectives of other “mature” cyclists here. What is your training focus as you age, and why?