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Medical Author:

Richard Weil, MEd, CDE

Richard Weil, MEd, CDE

Richard Weil, MEd, CDE, is an exercise physiologist and Certified Diabetes Educator, and is director of the New York Obesity Research Center Weight Loss Program at St. Luke's Roosevelt Hospital Center in

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Medical Editor:

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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How Does Resistance Exercise Work?

Resistance training works by causing microscopic damage or tears to the muscle cells, which in turn are quickly repaired by the body to help the muscles regenerate and grow stronger. The breakdown of the muscle fiber is called "catabolism," and the repair and re-growth of the muscle tissue is called "anabolism." You're probably familiar with the term anabolic when used with steroids. Anabolic means to grow, and that's exactly what happens after you break down the muscle fibers with resistance exercise. In fact, many biological processes of growth in the body require some breakdown, or catabolism, prior to re-growth. For instance, bones must be broken down first before calcium and other growth factors repair the bone and make it stronger. With muscles, testosterone, insulin-like growth factor, growth hormone, protein, and other nutrients rush to the muscle after a resistance-exercise session to help repair the muscles to make them stronger. Importantly, your muscles heal and grow when you aren't working out, and so that's why it's necessary to leave time between workouts for recovery.