I'll only speak from my experience of trying to exercise while on P2. I was a regular exerciser prior to starting. I ran on a pretty regular basis, so my body was used to it. On the second week I tried to run a bit, I did a 40 min run/walk mix and I was pooped. I probably was exercising at about a level 5 when I was used to going at about a 7 and it took every little ounce of energy right out of me. The next day I was overly sore and ravenous. So I thought that I would take it even easier and tried 40 min on the elliptical at a pretty easy pace. Same thing happened. So....I decided that apparently 500 calories isn't enough to sustain while exercising and I will just wait it out until I hit P3 then resume.
Now walking is an entirely different situation altogether, I can walk just fine, I have considered trying some easy yoga just because I miss exercise, but not much more than that. So, I don't know if I would start to add in any resistance types of exercises.