Muscle is a highly dynamic tissue that grows when stressed and shrinks when it is inactive. Most muscle physiologists believe that muscle damage is necessary for triggering muscle hypertrophy. A study from Northern Arizona University found that while muscle stress was important, muscles could hypertrophy without significant damage.
Researchers measured biochemical markers of muscle damage and muscle protein synthesis in trained and untrained people. The untrained subjects participated in stressful workouts that triggered inflammation and muscle damage, while the trained subjects practiced a more gradual workout that did not result in significant muscle damage. Increases in strength and muscle size were equal in both groups. Muscle hypertrophy can occur without significantly damaging muscle. (Journal Of Experimental Biology, 214: 674-679)