Resistance exercise training has been shown to have a positive effect on strength and functional status in the elderly. However, an acute bout of resistance exercise causes muscle soreness and may lead to transitory insulin resistance. Aging is often associated with the development of insulin resistance, hyperinsulinemia, diabetes mellitus and coronary artery disease. The extent to which aging per se is responsible for these health problems is not clear, as a decline in physical activity an changes in body composition can also be major contributing factors. One of the goals of this study is to determine whether an acute bout of resistance exercise which causes muscle soreness can alter basal and/or glucose-stimulated insulin release in a group (N=8) of older men and women (60-80 yr.). A second goal is to determine whether the response of older subjects differs to that of healthy young subjects (N=8, 20-30 yr). All subjects will perform a resistance exercise stress test which will include electrocardiographic monitoring and determination of one repetition maximum (1RM) strength for knee extension and bench press exercises. One of the exercise tests includes 16 sets of 10 concentric knee extension exercises at 75% of the predetermined concentric 1 RM and 16 sets of 10 reps of the concentric phase of the bench press exercise also at 75% of the predetermined bench press 1 RM. During the second exercise test the subjects will be required to perform 10 sets of 10 eccentric knee flexion exercises at 120% of 1 RM and 10 sets of 10 reps of the lowering phase of the bench press exercise at 120% of 1 RM. Three-day food records will be obtained prior to each exercise test and all meals will be provided during the 48 hour period between exercise tests and each clamp infusion study. Insulin pulsatility measurements, hyperglycemic (10 mM) clumps and C13-leucine infusions will be performed 48 hours after each exercise bout and after a control non-exercise period. Infusion of glucose (20% dextrose) will be used to measure the pancreatic insulin and c-peptide response. An infusion of the amino acid leucine (1 C13-leucine) will be used to assess rates of whole body protein turnover, oxidation and synthesis. Indirect calorimetry will be used to examine changes in anthropometrics and urinary creatinine excretion. Data from this project will provide information on the extent to which basal and glucose-stimulated insulin action can be affected by resistance exercise which causes muscle soreness in young and older men and women. The results from this study can contribute to understanding the mechanism by which exercise can impart metabolic control in the elderly.