I have the same issue . . . but I also know my motivation waxes and wanes. So some parts of the year I’m basically begging for rest days. I find it is more of a psychological phenomenon for me than a physiological one. If I’m in a training groove my body can be terribly sore, but I’m dying to do more work. Other times, I can feel completely fresh but the trainer seems like death.
Couple more thoughts:
I’m sure this is antithetical to everything a knowledgeable coach would say, but go have a light jog on some of your rest days. Not all running is created equal, nor does all running have to be terribly stressful. Find your “tempo” pace (i/e whatever feels like a sub-sweet spot effort) and go knock out 20-25 minutes of jogging. It will help with weight loss (if you’re trying to lose weight), it will take the edge of your antsy-ness for sure, and I don’t find (n=1) that it stresses my cycling muscles to the extent that I don’t recover.
If you went out for a run and hit it hard at something like a 5k race pace, then I’m sure it would be destructive – but let a jog be a jog, and I think you’ll be ok. If you’ve never really run before, then I’d run 3 mins / walk 3 mins to start to avoid injury for your first 4-5 times. Also – if you are a 40+ male (like me) weight bearing exercises, like running, are really good and really necessary for cyclists for bone density.
Also – and I’m kind of obsessed with this, but opinions here vary – do 20 to 30 minutes of body weight resistance work and core work. For instance: do 1 set of pull-ups, 1 set of push-ups, 1 set of planks . . . repeat and do that 3/4 times. You’ll feel like you had a workout for sure. This regimen doesn’t use any legs at all (or negligibly so) and it will make you way, WAY better on the bike from a posture/comfort/endurance perspective.
Hope this is helpful and good luck!