Specificity of training is a well-recognized principle of exercise physiology. Muscles adapt to the specific training stimulus imposed upon them: swimmers train by swimming, weight lifters train by lifting weights, football players train by running and throwing. These strategies have proven effective for athletes; however, they have not been applied to exercise regimes aimed at improving daily activities in older adults. Traditional exercise programs use endurance training, single joint strength training, or a combination of the two, but often they do not produce an improvement in functional measures (3). This traditional a p proach to exercise is prescribed for the general public with the intention of improving activities of daily living, yet they do not incorporate these activities into the training. Although resistance training using machines strengthens each muscle in isolation, these programs do not incorporate integrated performance into the training regime. Functional performance requires the integration of multiple joints and several muscle groups. In an activity such as stair climbing, the integrated strength of the quadriceps, hamstrings, hip flexors and extensors, and plantar flexors is involved. Merely strengthening each muscle in isolation does not train the muscles to work in a coordi- R29-AG10267; R01 AG10853; and ROI AG0754-02; the Dana Foundation; and the American Physiological Society. nated fashion to accomplish a multimuscle task, such as stair climbing.Recent research using resistive training in the older adult has been shown to increase muscle fiber area (4-7) and strength (4-7,12). The changes in strength with resistive training have been attributed to both neural adaptation (12) and muscle hypertrophy (4-7). However, the ultrastructural basis for changes in fiber area has not been investigated in the elderly nor has the ability of these programs to translate into functional performance been reported.The purpose of this study is to evaluate the ability of exercise training to change physical function and to investigate the underlying muscular changes responsible for change in function. This program used stair climbing with weighted backpacks as a resistive training stimulus. Muscle morphology, strength, and lower extremity functional performance were evaluated. Our evaluation incorpo-

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