How Muscles get Stronger

A report from Lenox Hill hospital in New York attempts to explain how exercising hard enough to cause muscle soreness makes muscles stronger. Competitive athletes do not train at the same intensity each day. They exercise vigorously enough to have their muscle burn while they are exercising, which damages their muscles to cause soreness on the next day, and then they take easier workouts to allow their muscles to heal before they take their next intense workout. Repeating bouts of muscle damage, and then allowing enough time for recovery, make the muscle stronger so it can withstand higher loads and is more resistant to injury.

Nobody really knows how these hard bouts make muscles stronger, but the most likely theory depends on the fact that hard exercise damages muscle fibers. Then other cells release chemicals called cytokines that cause inflammation characterized by soreness (pain), increased blood flow to the injured fibers (redness), and increased flow of fluid into the damaged area (swelling). The damaged muscle cells release tissue growth factors to heal the damaged muscle fibers, and if the athlete allows the muscle soreness to disappear before exercising intensely again, muscle fibers become larger and increase in number by splitting to form new fibers. If the athlete does not wait until the soreness goes away before exercising intensely again, the fibers can be torn, the athlete becomes injured, and the muscles weaken.

Athletes do not take off completely during recovery, even though resting when the muscles feel sore will allow the muscles to heal faster than exercising at a low intensity. If the athlete exercises at low intensity during recovery, his muscles will become more fibrous and resistant to injury when he stresses his muscles with the next intense bout of exercise.

Recent advances in the understanding of the repeated bout effect: the protective effect against muscle damage from a single bout of eccentric exercise. Scandinavian Journal of Medicine & Science in Sports, 2003, Vol 13, Iss 2, pp 88-97. MP McHugh. Lenox Hill Hosp, Nicholas Inst Sports Med & Athlet Trauma, New York,NY 10021 USA

Checked 4/1/15

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