You might notice larger arms right after a workout and think your muscles have grown. However, it is more likely caused by water retention. 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, swollen muscles occurring in the arm 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.
Read more: Water Retention in Muscles After Exercise
Muscle Anatomy and Physiology
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 through its tendon.
The breakdown of these tissues stimulates 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.
Muscle Breakdown and Buildup
The breakdown of the muscle fibers and the connective tissue in the arms causes 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 (DOMS), 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.
Eccentric exercise refers to the "negative" of a movement, such as lowering a weight back down after performing a biceps curl. Performing a warmup before working out and allowing at least one day of rest between workouts for the same muscle group can help prevent DOMS.
Arm Swollen After Workout
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.
Read more: Why Do You Swell After Workout?
Precautions and Warnings
A rare, but serious, medical condition called rhabdomyolysis can cause arm swelling after working out. This condition occurs when muscles begin to rapidly break down, releasing the contents of muscle cells into the bloodstream. In mild cases, a person might not have symptoms. However, in some cases, this is a life-threatening condition.
Rhabdomyolysis is most commonly caused by direct trauma to your muscle, but can also occur from overexerting your muscles. In addition to swelling, other signs and symptoms of this condition include muscle pain, weakness and tea-colored urine.
You might also experience nausea, vomiting, bruising, fever or confusion. Seek immediate medical attention if you suspect you have this condition to prevent permanent kidney damage from occurring. To help prevent rhabdomyolysis from occurring, drink plenty of fluids before you work out and during exercise, according to Healthline.