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Exercise within lower body negative pressure partially counteracts lumbar spine deconditioning associated with 28-day bed rest

¹Department of Orthopaedic Surgery, University of California-San Diego, San Diego, California; ²Division of Orthopedic Surgery, Department of Regenerative and Transplant Medicine, Niigata University Graduate School of Medical and Dental Sciences, Niigata City, Japan; and ³Sleep Consultants, Inc., Fort Worth, Texas

Submitted 21 December 2004 ; accepted in final form 7 March 2005

Astronauts experience spine deconditioning during exposure to microgravity due to the lack of axial loads on the spine. Treadmill exercise in a lower body negative pressure (LBNP) chamber provides axial loads on the lumbar spine. We hypothesize that daily supine LBNP exercise helps counteract lumbar spine deconditioning during 28 days of microgravity simulated by bed rest. Twelve sets of healthy, identical twins underwent 6° head-down-tilt bed rest for 28 days. One subject from each set of twins was randomly assigned to the exercise (Ex) group, whereas their sibling served as a nonexercise control (Con). The Ex group exercised in supine posture within a LBNP chamber for 45 min/day, 6 days/wk. All subjects underwent magnetic resonance imaging of their lumbar spine before and at the end of bed rest. Lumbar spinal length increased 3.7 ± 0.5 mm in the Con group over 28-day bed rest, whereas, in the Ex group, lumbar spinal length increased significantly less (2.3 ± 0.4 mm, P = 0.01). All lumbar intervertebral disk heights (L₅–S₁, L_4–5, L_3–4, L_2–3, and L_1–2) in the Con group increased significantly over the 28-day bed rest (P < 0.05). In the Ex group, there were no significant increases in L₅–S₁ and L_4–5 disk heights. Lumbar lordosis decreased significantly by 3.3 ± 1.2° during bed rest in the Con group (P = 0.02), but it did not decrease significantly in the Ex group. Our results suggest that supine LBNP treadmill exercise partially counteracts lumbar spine lengthening and deconditioning associated with simulated microgravity.

simulated microgravity; lumbar spine length; intervertebral disk height; spinal curvature; countermeasures

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