The increased blood flow and vasodilation enhances the speed at which the body repairs itself, (hypertrophy). Muscle biopsies taken on the day after rigorous exercise show bleeding and disruption of the z-band filaments that hold muscle fibers together as they slide over each other during a contraction. While increased blood flow (vasodilation) does help remove ammonia and lactic acid from the muscle, as well as feed the muscle nutrition, the actual soreness is caused by microscopic tears in the muscle fiber, not caused by a build-up of lactic acid or ammonia.
We suggest you train on one day repetitively to muscle burn, then back off and repeat this cycle 3-to-5 times and let the muscle rest for 3 days or one week. Only then increase the resistance if muscle volume and strength is desired.