Lower body negative pressure treadmill exercise as a countermeasure for bed rest-induced bone loss in female identical twins

Abstract

Supine weight-bearing exercise within lower body negative pressure (LBNP) alleviates some of the skeletal deconditioning induced by simulated weightlessness in men. We examined the potential beneficial effect in women. Because dietary acid load affected the degree of bone resorption in men during bed rest, we also investigated this variable in women. Subjects were 7 pairs of female identical twins assigned at random to 2 groups, sedentary bed rest (control) or bed rest with supine treadmill exercise within LBNP. Dietary intake was controlled and monitored. Urinary calcium and markers of bone resorption were measured before bed rest (BR) and on BR days 5/6, 12/13, 19/20, and 26/27. Bone mineral content was assessed by dual-energy X-ray absorptiometry before and after bed rest. Data were analyzed by repeated measures two-way analysis of variance. Pearson correlation coefficients were used to define the relationships between diet and markers of bone metabolism, and to estimate heritability of markers. During bed rest, all markers of bone resorption and urinary calcium and phosphorus increased (P < 0.001); parathyroid hormone (P = 0.06), bone-specific alkaline phosphatase (P = 0.06), and 1,25-dihydroxyvitamin D (P = 0.09) tended to decrease. LBNP exercise tended to mitigate bone density loss. The ratio of dietary animal protein to potassium was positively correlated with urinary calcium excretion for all weeks of bed rest in the control group, but only during weeks 1 and 3 for the exercise group. Pre-bed rest data suggested that many markers of bone metabolism have strong genetic determinants. Treadmill exercise within LBNP had less of a protective effect on bone resorption during bed rest in women than previously-published results had Sources of support: This study was funded by NASA through grant NAG 9-1425 and by NIH through grant GCRC M01-RR00827 to UCSD.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. shown for its effect in men, but the same trends were observed for both sexes. Dietary acid load of these female subjects was significantly correlated with calcium excretion but not with other bone resorption markers. NIH Public Access

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“…These effects can be seen primarily in the Shackelford et al 2004 study in Figure 51 and impact on any resorption marker; only LBNP with a vertical treadmill was effective at lessening the increase in NTX and deoxypyridinoline (Smith et al 2003). Interestingly, this same protocol was effective for male twins (Smith et al 2003), but was ineffective for female twins (Zwart et al 2007) …”

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