Swelling is an enlargement of a body part caused by fluid accumulation within tissue. If it occurs throughout the body, then swelling may be an overt symptom of a more significant problem. However, swelling that occurs in the arm muscles after a workout is a normal part of recovery. The best way to deal with swelling is to rest until the symptoms begin to diminish.
Muscle anatomy has two major components. The muscle fibers, made from a series of bundled proteins, compress and contract to move and exert force. Subsequently, the fibrous bands of connective tissue transmit the pull of the muscle to the bone. The breakdown of these tissues stimulate the body to build bigger and stronger fibers so that they can sustain more pressure and force. This process of swift growth and adaptation is known formally as muscle hypertrophy.
Breakdown of the muscle fibers and the connective tissue in the arms cause injury and damage to the tissue. This is the source of pain and discomfort in the days following a strength-training session. Swelling is usually a symptom of a condition called delayed-onset muscle soreness, which occurs after people engage in the kind of difficult and stressful exercise to which they are unaccustomed. It is most likely to happen following an eccentric exercise, in which the external force is greater than the force that the muscle can generate, causing the fibers to lengthen.
According to a 1993 study published in "The Journal of Physiology" by researchers from Ohio University, swelling proceeds in two major phases. Immediately after exercise the arm circumference increases by about 3 percent total. Following a brief period when the swelling subsides, the arm circumference increases by 9 percent and remains elevated for as long as nine days, persisting long after the accompanying soreness and pain diminishes. The only symptom that outlasted swelling was a loss of strength, which persisted for as long as five to six weeks.
The fluid accumulation that causes swelling in the muscles is produced by the injured cells to trigger an immune response. This immune response is needed to clean out the damage in the cells that accumulates during the course of the workout. Though the immune response may last for more than a week, a workout can usually be undertaken again two or three days after the previous one. The muscles are not required to completely heal first.