Many years ago, I found a website that claimed to know about what the road pros do in the gym. Of course, only their coaches really know, but . . . They concentrate on squats and work to near failure on the last set. They start in the fall with high reps, as many as 15 IIRC. I wouldn't say light weights, because these folks are strong! So, I should say lighter weights. They gradually decrease the reps and increase the weights over the months between fall and their events. They'll be doing sets of 4 reps, having worked up to very heavy squats before they stop lifting for the season. I've modeled my gym work after theirs. My weights are much lighter, but the idea is the same. It's simple and easy to program. Also, being a geezer, I do full-body workouts and put on much more upper body muscle than a pro, though I use a similar progression for everything.

One of the most famous modern road pros had gym videos up for maybe a couple weeks, then they were taken down. That's the only first-person pro-roadie gym stuff I've ever seen published.

Referring to Dylan's video above, that's what's worked for me with caveats noted above. I lift twice a week, full-body workouts, with one day mostly pushing work, the other is mostly pulling.