How about a back injury that caused you to miss five years? That's me. I tried a comeback earlier in the year, but I failed at it because I went straght back into the basic lifts (squats, cleans, benches). Even though I went light, the limiting factor of my weak, atrophied back muscles made these impossible, as well as hormonal issues.
So in my recent comeback, I joined a gym and for the first month didn't touch a barbell, did just treadmill for cardio 4 days a week, and one machine per bodypart twice a week. My mind said I was undertraining but my body would get tired out just fine. I listened to me back and there was even a few machine exercises that made my back hurt (cable pulley rows for lats, for example), and I stayed away from them.
The second month I introduced variety into cardio, and started SOME barbell work, but did hacks instead of barbell squats, and alternated barbell presses and cleans with machine presses and machine shrugs. Everything kept going great, muscles responding, back fine, felt like a new man.
The third month, however, I got carried away-which is the source of my thread. Don't read it, read Shugart and Robertson and the other smart guys on T-Nation. Seriously.