What you are doing is good for your endurance, i.e. small weight with a lot of rep, but no more than 20-25. If you can lift weight for more than 25 rep (you need to be EXHAUSTED at the end and NOT ABLE to make another rep) then what you are doing does (almost) nothing to your body.
Your muscles will get more endurance, but they won't be stronger/bigger, and won't really change your body composition.
However, if you want muscle strenght/mass, you need to lift heavy weight (3-6 rep until you are exhausted).
Last edited by Magalo : 04-05-2012 at 01:15 AM.