PTH And Calcium Responses to Exercise in Older Adults Experiment 2 (PACE Sr. 2)

Inclusion Criteria: * Healthy adults aged 60-80 y * Currently taking a bisphosphonate medication Exclusion Criteria: * Use of medications (other than bisphosphonates) in the past 6 months known to affect bone metabolism (e.g., thiazide diuretics, oral glucocorticoids) * Bone Mineral Density (BMD) t score \< -3.0 at the total hip or lumbar spine * Known disease or condition associated with intestinal malabsorption * Moderate or severe renal impairment defined as an estimated glomerular filtration rate of \<60 mL/min/1.73m2 based on the Modified Diet in Renal Disease (MDRD) equation * Chronic hepatobiliary disease, defined as liver function tests (AST, ALT) \>1.5 times the upper limit of normal; if such values are obtained on initial screening and thought to be transient in nature, repeated testing will be allowed * Thyroid dysfunction, defined as an ultrasensitive TSH \<0.5 or \>5.0 mU/L; volunteers with abnormal TSH values will be re-considered for participation in the study after follow-up evaluation by the PCP with initiation or adjustment of thyroid hormone replacement * Serum calcium \<8.5 or \>10.3 mg/dL Serum 25(OH)D \<20 ng/mL; volunteers with abnormal serum 25(OH)D values may be re-considered for participation in the study if serum 25(OH)D is \>20 ng/mL after vitamin D supplementation * Uncontrolled hypertension defined as resting systolic BP \>150 mmHg or diastolic BP\>90 mmHg; participants who do not meet these criteria at first screening will be re-evaluated, including after follow-up evaluation by the PCP with initiation or adjustment of anti-hypertensive medications * History of type 1 or type 2 diabetes * Cardiovascular disease; subjective or objective indicators of ischemic heart disease (e.g., angina, ST segment depression) or serious arrhythmias at rest or during the graded exercise test (GXT) without follow-up evaluation will be cause for exclusion; follow-up evaluation must include diagnostic testing (e.g., stress echocardiogram or thallium stress test) with interpretation by a cardiologist * Diagnosis or history of asthma