Effects of an astronaut microgravity countermeasure skin suit on lumbar geometry and kinematics: A prospective cohort study.

Purpose: Astronauts returning from long ISS missions have demonstrated an increased incidence of lumbar disc herniation associated with biomechanical and morphological spine changes. This research describes a ground-based study of the effects of an axial compression countermeasure Mk VI SkinSuit designed to reload the spine and reduce these changes before return to terrestrial gravity. Methods: Twenty healthy male volunteers aged 21-36 without back pain participated. Each lay overnight on a Hyper Buoyancy Flotation (HBF) bed for 12 hours on two occasions 6 weeks apart. On the second occasion participants donned a Mk VI SkinSuit designed to axially load the spine at 0.2Gz during the last 4 hours of flotation. Immediately after each exposure, participants received recumbent MRI and flexion-extension quantitative fluoroscopy scans of their lumbar spines, measuring differences between spine geometry and intervertebral kinematics with and without the SkinSuit. This was followed by the same procedure whilst weight bearing. Paired comparisons were performed for all measurements. Results: Following Mk VI SkinSuit use, participants evidenced significantly more flexion RoM at L3-4 (p=0.01) and L4-5 (p=0.003), more translation at L3-4 (p=0.02), lower dynamic disc height at L5-S1 (p=0.002), lower lumbar spine length (p=0.01) and greater lordosis (p=0.0001) than without the Mk VI SkinSuit. Disc cross-sectional area and volume were not significantly affected. Conclusion: The morphology and kinematics of the lumbar spine are significantly influenced by the SkinSuit in directions negatively associated with post-spaceflight disc herniation. This may help inform physiological countermeasures to maintain spinal health during long-duration missions in space