Parameters of Exercise to Prevent Osteoporosis

A. Hypotheses and specific aims:

Specific aim 1. Measure plasma concentrations of anabolic hormones (parathyroid hormone (PTH) and growth hormone (GH), at sufficient frequency to define the area under the curve (AUC), and of markers of bone formation (osteocalcin, carboxyterminal propeptide of type 1 procollagen (CICP), and bone-specific alkaline phosphatase (ALKP)), and markers of bone resorption (immunoreactive carboxyterminal telopeptide of type I collagen (CTX)) after 40-minutes of treadmill exercise at the relative intensity of 125% of the ventilatory threshold (VT) corresponding to about 1.78 m/sec (4 miles/h), and two intensities of mechanical loading (724, and 1411 N), in healthy postmenopausal women.

Hypothesis 1. Bone formation, as assessed by increases in markers of bone formation and decreases in markers of bone resorption, will be higher in response to dynamic exercise at a level of mechanical loading that produces increased secretion of PTH and GH than to exercise at other loading intensities.

Specific aim 2. Measure plasma concentrations of anabolic hormones), at sufficient frequency to define the area under the curve (AUC), and of markers of bone formation as in specific aim 1, after two 20-minutes of treadmill exercise, separated by 7 h, at the relative intensity of 125% of the ventilatory threshold (VT) corresponding to about 1.78 m/sec (4 mi/h), and two intensities of mechanical loading (724, and 1411 N), in healthy postmenopausal women.

Hypothesis 2. A 7-hour interval separating the two bouts of exercise will have greater bone anabolic effect than the equivalent volume and intensity of exercise performed in a single bout.

Inclusion criteria

• Age 50 to 65 years if naturally post-menopausal, or age 47 if surgically postmenopausal
• Dual energy X-ray absorptiometry (DEXA) Z score above -1
• No endocrine or metabolic disease requiring medication except for hormonally corrected hypothyroidism
• No musculo-skeletal disabilities that would preclude treadmill walking
• Normal electrocardiogram (EKG) and heart health history
• BMI between 24 and 30
• Hematocrit above 32 %
• No hormone replacement therapy (HRT)
• Personal health provider's Release Letter

Exclusion criteria

• Age and BMI outside of the specified range
• Z score below -1
• Medication for presence of metabolic or endocrine disease
• Musculo-skeletal disabilities that would preclude treadmill walking
• Abnormal electrocardiogram (EKG) and heart health history
• Hematocrit below 32%
• Hormone replacement therapy
• Failure to conform to study protocol