Cycled Testosterone Replacement Study

Inclusion Criteria: * Availability of transportation (i.e., subjects must be able to provide their own transportation to UTMB). Exclusion Criteria: * Medications such as anticoagulants (Coumadin) and glucocorticoids. * History of angina that occurs with exertion or at rest. * History of myocardial infarction within the last 12 months. * Failure to successfully complete an exercise stress test using the Bruce protocol. Subjects that demonstrate ≥ 0.1 mV horizontal or downsloping ST segment depression, a drop in systolic blood pressure of ≥ 10 mm Hg, and/or frequent or repetitive arrhythmias (defined as ≥ 10 PVC/min, or couplets) during the stress test will be excluded. * LDL cholesterol above 200 mg/dL. * History of prostatic cancer. * Elevated prostate specific antigen (PSA) above 4.0 µg/L, or severe benign prostatic hypertrophy (BPH) by history (frequent urination, reduced stream). * Serum total testosterone concentrations of greater than 500 ng/dL. * Subjects who engage in high intensity, elite training on a regular basis. * Major medical illness such as diabetes, chronic obstructive pulmonary disease, or sleep apnea. * Recent history of smoking tobacco. * Hematocrit greater than 51%. * Morbidly obese older men (BMI \> 35). * Hypertension: Blood pressure on three consecutive measurements taken at one week intervals that has a systolic pressure ≥ 140 or a diastolic blood pressure ≥ 90. Subjects will be included if they are on two or less blood pressure medications and have a blood pressure below these criteria. * History of hepatitis or a 3-fold elevation of liver function tests (Alk phos, ALT, AST). * Bone related disorders such as osteoporosis or parathyroid disease. * DEXA scans revealing lumbar spine T-scores of less than -2.5. * Subjects currently taking anti-bone-resorptive agents such as bisphosphonates, parathyroid hormone, or calcitonin.