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Resistance exercise as a countermeasure to disuse-induced bone loss

¹National Aeronautics and Space Administration Johnson Space Center, Houston 77058; ²Department of Medicine, Baylor College of Medicine, Houston 77030; ³Division of Space Life Sciences, Universities Space Research Association, Houston 77058; ⁴Wyle Laboratories Life Sciences Systems and Services, Houston 77058; and ⁵School of Public Health, University of Texas, Houston, Texas 77030

Submitted 16 July 2003 ; accepted in final form 16 March 2004

During spaceflight, skeletal unloading results in loss of bone mineral density (BMD). This occurs primarily in the spine and lower body regions. This loss of skeletal mass could prove hazardous to astronauts on flights of long duration. In this study, intense resistance exercise was used to test whether a training regimen would prevent the loss of BMD that accompanies disuse. Nine subjects (5 men, 4 women) participated in a supine maximal resistance exercise training program during 17 wk of horizontal bed rest. These subjects were compared with 18 control subjects (13 men, 5 women) who followed the same bed rest protocol without exercise. Determination of treatment effect was based on measures of BMD, bone metabolism markers, and calcium balance obtained before, during, and after bed rest. Exercisers and controls had significantly (P < 0.05) different means, represented by the respective following percent changes: lumbar spine BMD, +3% vs. –1%; total hip BMD, +1% vs. –3%; calcaneus BMD, +1% vs. –9%; pelvis BMD, –0.5% vs. –3%; total body BMD, 0% vs. –1%; bone-specific alkaline phosphatase, +64% vs. 0%; alkaline phosphatase, +31% vs. +5%; osteocalcin, +43% vs. +10%; 1,25 dihydroxyvitamin D, +12% vs. –15%; parathyroid hormone intact molecule, +18% vs. –25%; and serum and ionized calcium, –1% vs. +1%. The difference in net calcium balance was also significant (+21 mg/day vs. –199 mg/day, exercise vs. control). The gastrocnemius and soleus muscle volumes decreased significantly in the exercise group, but the loss was significantly less than observed in the control group. The results indicate that resistance exercise had a positive treatment effect and thus might be useful as a countermeasure to prevent the deleterious skeletal changes associated with long-duration spaceflight.

microgravity; bed rest; bone resorption; bone formation; strength training

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