Parameters of Exercise to Prevent Osteoporosis (OSTEOPOROSISEX)

University of Wisconsin, La Crosse, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

The principal goal of this study is to determine parameters of walking in terms of peak mechanical vertical force, bout duration, and bout spacing that can preserve or increase bone mineral density (BMD) in postmenopausal women. Release of pulses of parathyroid hormone (PTH), growth hormone (GH), and of markers of bone resorption and bone formation will be used as indicators of the osteogenic effects of a short exposure to exercise. When secreted in pulsatile fashion, GH stimulates osteoblast proliferation, particularly in cortical bone (27, 28). Like GH, the pattern of PTH secretion determines the nature of its effect on bone. When it is secreted in pulsatile manner, PTH contributes to bone formation through activation of bone lining cells, differentiation of osteoprogenitor cells, and suppression of bone cell apoptosis .

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.

Five parallel groups, matched for age and BMI, where exercise was applied at 6o uphill or 6o downhill either as one 40-min morning bout or as two 20-min half bouts distributed 7 h apart. A sedentary group served as a control for the four exercise groups.

Subjects were subjected to 40 minutes of treadmill exercise at a 6 degree incline and at 75% of maximal effort between 8:00 and 8:40 am. Isocaloric meals were provided at 7:00, 13:00. and 19:00 h.

Subjects were subjected to 40 minutes of treadmill exercise at a 6 degree decline and at 45% of maximal effort between 8:00 and 8:40 am. Isocaloric meals were provided at 7:00, 13:00. and 19:00 h.

Subjects were subjected to two 20 minutes of treadmill exercise separated by 7 h at a 6 degree incline and at 75% of maximal effort, the first one between 8:00 and 8:40 am and the second one between 15:00 and 15:20 h..Isocaloric meals were provided at 7:00, 13:00. and 19:00 h.

Subjects were subjected to two 20 minutes of treadmill exercise separated by 7 h at a 6 degree incline and at 45% of maximal effort , the first one between 8:00 and 8:40 am and the second one between 15:00 and 15:20 h. Isocaloric meals were provided at 7:00, 13:00. and 19:00 h.

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