A 16-inch bicep is attainable, depending on the overall health of the individual. The average bicep size for a nationally ranked bodybuilder is between 19 1/4 and 19 5/8 inches. Arnold Schwarzenegger is said to have had 22-inch biceps during his professional bodybuilding career.
Genetic factors, such as muscle fiber construction and hormone levels, determine the natural size of biceps; however, supplementation may increase this natural threshold. Muscle growth, known as hypertrophy, is caused by traumatizing muscle fibers through exercise. In response to resistance training, satellite cells around muscles increase in size and strength through complex biological processes. People can promote hypertrophy by consuming 2.2 grams of protein per pound of lean body weight and resting at least 48 hours between weight-training sessions.