Effects of Resistance Training: Given an adequate training stimulus, older adults can make significant gains in strength. A two- to threefold increase in strength can be accomplished in three to four months in fibers recruited during training in older adults. With more prolonged resistance training, even a modest increase in muscle size is possible. Because sarcopenia and muscle weakness are so prevalent in the aging population, it is important to devise strategies for preserving or increasing muscle mass in the older adult. With increasing muscle strength come increased levels of spontaneous activity in both healthy, independent older adults and very old and frail men and women. Strength training, in addition to its possible effects on insulin action, bone density, energy metabolism, and functional status, is also an important way to increase levels of physical activity in the older adult.