Skinny to Strong

When I first started P90X I could barely do a couple of chin-ups. But in P90X video I see people doing 15 and 20 reps and that is not just in the first set. They consistently do as many chin-ups in every set. I used to question whether I can ever be so strong. I always hated my chin-up days. Not anymore. How did I do it? I just kept doing them even though I could only get 2 or 3. When I could not do any more I used to do negatives. For this I would jump to the chin-up bar so that I am in the top most position. Then I slowly came down. I kept doing it for all the sets where I could not get even 1 rep. Coming down slow is the key. I kept doing as many negative reps as I could get without hurting myself. The next time I did chin-ups I could get 1 or 2 extra reps! That worked very well. I later found another trick that helped me get more energy. The trick is to tighten the abs as I am doing chin-ups. This helped me do a few more reps. I am not doing negatives any more because now I can...