Here's a great video talking (and demoing) lactic acid training. The physiology is apparently that lactic acid build up prompts growth hormone production which builds muscle and liquidates fat. The trainer here suggest going slow on the positive (work) portion of movements and then snapping back to the starting point again.
So going slowly up in a push up and quickly dropping down to go again. Going slowly up from a squat and quickly dropping back down to the starting position. This is supposed to optimize lactic acid production.
Check out the video for a great demo.