There has been some new evidence as of late, that suggest that when an individual's lactate threshhold is crossed, they see an increase in fat burning. Now, there are many ways to cross the lactate threshold. One of which is elevating the rep count i.e. 10 -20 up to 100. Another technique is by lowering rest intervals (from 120 sec. to 30 sec.) Yet another technique, is time under tension, or extending the length of the actual set. Personally I have seen good results by mixing the three. I do a heavy compound movement to begin, then after a short rest I will move to another exercise and rep it out a bit. (12 reps is a lot for me.) Utilizing these techniques, have helped me lean out quite well while maintaing a good amount of muscle.