With all of these recent interruptions to my training, I've had to start over a lot with different exercises. The other night I did some upper-body weight-lifting, which I hadn't done in a while. So I went very conservatively, just doing two kinds of push-ups, lat pulls, and pull-ups (on top of my normal physical therapy). As I was walking out of the gym, I didn't feel worn out, so I was unsure if I had even gotten enough of a workout in. But the next day, my pecs and lats said otherwise. They weren't catastrophically sore, but enough to feel it.
At the beginning, I think this is the best way to go. If I had gone all out that night and lifted until I couldn't lift any more, I would have been hurting for a week afterwards, which would have majorly delayed my next hard workout. Once a certain muscle group gets used to the effort, I think it is good to max out when you lift, then take a couple of days off from working those same muscles. But at the start, the recovery from that kind of intense effort is so long that it keeps you from working out again soon.
Some people probably recommend hitting it hard at that start, because you would make more progress in each workout. But I think the needed extra days off will end up costing you more in potential growth then what you would gain. The nice thing about strength training is that it has a steep learning curve, so after just one or two workouts those muscles are probably ready to go full-bore.
For some motivation, here is a pic of the master of muscles, Mr. Universe himself: