How Muscles Heal From a Hard Workout

The muscle soreness felt after a tough workout is a sign that you’re on the way to increased strength. Moderate to intense resistance training produces immediate muscle fatigue and latent muscle soreness; it boosts strength, increases muscle tone and, in some cases, builds muscle size. As with most biological responses though, the process is complex and multidimensional.

  1. Work It Out

    • Muscle tone and strength are gained when a muscle encounters increasing amounts of resistance. Thus, in order to continually gain muscle mass, you must continually increase the amount of weight lifted or number of repetitions performed. During resistance training, muscle fibers and their connective tissues sustain tiny tears and these tears are recognized as trauma by the body. At the first sign of distress the immune system kicks into high gear, initiating a chain of reactions to repair what it has deemed as damaged skeletal muscle.

    The Fix-It Team

    • Satellite cells, which facilitate muscle growth and repair, are the first responders. Once activated by muscle trauma, they begin multiplying and their new “daughter” cells fuse with existing muscle fibers, aiding in regeneration. This fusion increases the size of existing muscle fibers. It does not, however, create more muscle fibers. In addition to the satellite cell response, the immune system triggers a sequence of events which leads to inflammation. Inflammation contains and repairs the damage, as well as cleans up waste products. As part of this response, white blood cells begin to secrete cytokines -- proteins that help cells communicate with one another -- and other growth factor proteins. The cytokines call additional “healer” cells, such as neutrophils, monocytes and lymphocytes, to the area and they all work together to repair the injured tissues. This is done by breaking down the growth factor proteins, removing damaged cells and controlling the inflammation; this process leads to muscle hypertrophy, or exercise-induced muscle growth.

    Harder, Better, Faster, Stronger

    • The end result of muscle repair is a thickening of the muscle fibers which increases the muscle’s diameter and mass. This increase in muscle hypertrophy leads to an increase in strength or force production; the muscle is both bigger and stronger. Testosterone plays a large role in hypertrophy, as it increases protein synthesis which helps muscles grow. Since men naturally have more testosterone than women, men can hypertrophy -- grow muscle -- to a greater extent and more easily than women.

    No Pain, No Gain

    • Moving from muscle fatigue to muscle repair and growth takes time. Anyone who has engaged in moderate to intense weight-bearing exercise is likely keenly aware of the muscle soreness that can set in one to three days after a workout. Delayed onset muscle soreness, or DOMS, is evidence of the muscle repair and growth process. The American Council on Exercise suggests refraining from exercising the sore muscle group for one to three days or until the soreness has subsided, to allow appropriate time for muscle repair.