Active vs. inactive muscle:

People may lose 20 to 40 percent of their muscle -- and, along with it, their strength -- as they age. Scientists have found that a major reason people lose muscle is because they stop doing everyday activities that use muscle power, not just because they grow older.
- Reviewed last on: 11/30/2008
- David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Daniel B. Hoch, PhD, MD, Assistant Professor of Neurology, Harvard Medical School, Department of Neurology, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.