I’m chiming in very late. But I think I have a bit of experience with this.
I primarily lift and use cycling and running for general fitness / cardio. When I first started focusing on cycling instead of running, I joined TR. At the time, I was lifting six days a week on a three-day split (two leg days). Leg days involved ~120 reps spread over 12-16 sets (depending on the day).
I started SSB 1 and 2 LV. My initial plan was to do my best to avoid cycling on leg days. I then amended that plan to avoid cycling the day after leg day, and to do my best to avoid it on leg day and the day before leg day. As you can imagine, I ran out of days (damn weeks only have seven of them). It meant that there was one day a week I was cycling that was either on leg day or the day before it. But that was still better than cycling the day after a leg day.
That plan ended up working great. I had already gotten close to plateauing my leg lifts (without adding calories and gaining weight). During SSB 1 and 2, I lost no strength. My FTP from ramp tests continued to rise, too (significantly). It was great, if tiring. Some days were tough, no question.
Then I started the build phase. Everything fell apart. I overtrained. I got weaker in my leg lifts (on some days, 25% weaker), and I was routinely failing TR workouts. I kept at it for three weeks. But it just got worse. I decided to stress cycling and focus less on leg lifts (I dropped one of the two leg days). Sadly, because I never rested after the initial overtraining, it didn’t matter. I didn’t recover. Three more weeks later, I was done. I stopped all cardio and only lifted four days a week (dropped both leg days). I waited two months to reincorporate leg days and two running days.
I never figured out if it was the whole leg day and cycling thing, or if it was that I was just not “built” for the build phase. I am older than you (45). And I’ve read other posts about people in my age group and older that struggle with the build phase without any lifting. But I have to think the two were related.
If I were to ever repeat it (I haven’t; it was that bad; I felt terrible those three weeks, and everything suffered), I would dial back leg day to once a week, and I would dial back the number of sets and reps (maybe 6 sets of 12 reps at weights that I could complete all reps, i.e., avoiding complete fatigue). I feel like that load would have worked.
I never restarted structured cycling training. I ride for fun with friends, and that’s it. While I’m sure my FTP is way lower than it was, I still think it’s higher than when I started. I lost a lot but not all. I run for cardio now.
My $.02, which is probably worth even less than that.
Will