Exercise will stimulate a positive change if the body is allowed to recover and repair itself. Exercise too soon, the repair process won’t be complete, and you won’t be at the 100 percent level necessary to stimulate more positive change. It will be wasted effort; you’ll ruin two workouts. How much recovery time is needed will depend on the type of exercise.
Aerobic exercise requires a persistent stimulus to improve; anaerobic exercise does not. The changes resulting from aerobic exercise are primarily biochemical, and take a relatively short time to occur.
Anaerobic exercise such as strength training produces biochemical and structural changes. After strength training, the body attempts to repair the micro-trauma resulting from stressing the muscles, bone, and connective tissue. This trauma, like a cut or a bruise, takes time. Given adequate time to recover you will come back stronger and be able to build on those improvements.