This isn't directly analogous, but I'm also an ex-runner, now a cyclist, and I used to have trouble making myself take days off.
Last summer and fall I spent three months in a hospital and inpatient rehab for a rare condition, including eight weeks essentially flat on my back. At one point I didn't have the strength to work the TV remote. The inactivity made me so weak I couldn't walk or even turn on my side in bed. It's taken six months of therapy to get back to a relatively normal life, walking and driving and (soon) riding short distances.
But here's the relevant part: during the therapy, which was by far the hardest work I've ever done, I saw progress much faster than in normal exercise. For a long time, I literally got measurably stronger every day--but if I didn't take a day off or at least cut way back about every fourth day, I stopped progressing. Rest a day, and things picked up again.
Does that apply to normal exercise for normal people? I can't prove it, but I can't think why it wouldn't to at least some degree.