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. Although increased blood flow (vasodilation) helps remove ammonia and lactic acid from the muscle and nourish the muscle, the actual pain is caused by microscopic tears in the muscle fibers and not by an accumulation 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.