Vastus lateralis muscle biopsies have been collected from all of the squirrel monkeys. The samples were frozen for processing. Biochemical and histological analysis of the muscle samples is complete and the data are being analyzed. Assays include myosin ATPase activity for determination of muscle fiber type, proportions, and cross-sectional area. Preliminary data indicate an age-related decline in type II fibers, consistent with other species. A grip strength apparatus was developed and monkeys are currently being trained to use it. Data indicate a decrease in grip force with age. Grip force will provide a functional measure of muscle strength and an approximation of maximal grip force. As proof of principle for a disuse model, a monkey's arm was casted for 2 weeks. In subsequent grip testing, max force had decreased by approximately 30%. Further testing is planned.