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

Participants will undergo two identical walking exercise sessions on a treadmill. One session
will occur until continuous calcium infusion and the other will be under continuous saline
infusion. C-telopeptide, parathyroid hormone, total calcium, and serum ionized calcium will
be monitored to distinguish differences in bone activity under the two conditions.

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