Repeated bout effect is the term for the well-known phenomenon by which exercise-induced muscle soreness tends to abate with successive workouts. Now, researchers at Brigham Young University report that they have discovered how the immune system acts to repair muscle damage and prevent additional injury. Writing in the journal Frontiers in Physiology, the team concludes that T-cells were found to infiltrate muscle fiber in response to exercise-induced damage. Although traditionally associated with response to infections, the presence of the T-cells in muscle fiber suggests that muscles become more effective at recruiting immune cells following a second bout of exercise and that these cells may facilitate accelerated repair.
The team additionally noted that their study subjects exhibited increased inflammation after a second round of exercise—contrary to previous belief that inflammation goes down with repeated exercise, contributing to less soreness. Lead author Michael Deyhle commented, "Many people think inflammation is a bad thing. But our data suggest when inflammation is properly regulated it is a normal and healthy process the body uses to heal itself." An implication of this secondary finding is that the use of anti-inflammatory medications such as ibuprofen or aspirin after exercise may not be as effective as previously thought.
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Read a news story about the findings here.
The journal article may be read here.