‘Use it or lose it’ is a primary rule that muscle cells obey, and the same is true of brain cells. The body cannot afford to waste energy building, supporting and managing muscle cells or other cells that do not contribute to the overall life of the body. The best signal that the body gets to tell it that muscle is required is when the muscle is placed under regular (though moderate) stress and strain. If an organ is working, it is being used, and if it is being used, it needs to be maintained. The muscles of people who are relatively sedentary for long periods of time start to change, with
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