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

Calcium (as either calcium chloride or calcium gluconate in half normal saline) will be delivered via IV during exercise to keep serum ionized calcium levels above baseline. The clamp is modeled after the hyperglycemic glucose clamp.

This is the placebo comparative infusion. Half-normal saline will be infused at the second collection visit following the identical infusion schedule determined during the calcium infusion visit.