This soreness you may feel is called delayed onset muscle soreness (DOMS) and is experienced by many that have started a new exercise program. The soreness results from high force production when an exercise is new or a when a load is greater than normal. During eccentric muscle contractions (in which the muscle lengthens), small microtears occur in the muscle fibers. This is common and affects most exercisers during the first 24 hours post-exercise. It typically peaks in the next 48 hours and then subsides.