changes in intervertebral disc morphology persist 5 mo after 21day bed rest as part of the nutritioncountermeasures nuc study in cologne germany in 2010 seven healthy male subjects underwent 21 days of headdown tilt bed rest and returned 153 days later to undergo a second bout of 21day bed rest as part of this model we aimed to examine the recovery of the lumbar intervertebral discs and muscle crosssectional area csa after bed rest using magnetic resonance imaging and conduct a pilot study on the effects of bed rest in lumbar muscle activation as measured by signal intensity changes in t2weighted images after a standardized isometric spinal extension loading task the changes in intervertebral disc volume anterior and posterior disc height and intervertebral length seen after bed rest did not return to prebedrest values 153 days later while recovery of muscle csa occurred after bed rest increases p 0016 in multifidus psoas and quadratus lumborum muscle csa were seen 153 days after bed rest a trend was seen for greater activation of the erector spinae and multifidus muscles in the standardized loading task after bed rest greater reductions of multifidus and psoas csa muscle and greater increases in multifidus signal intensity with loading were associated with incidence of low back pain in the first 28 days after bed rest p 0044 the current study contributes to our understanding of the recovery of the lumbar spine after 21day bed rest and the main finding was that a decrease in spinal extensor muscle csa recovers within 5 mo after bed rest but that changes in the intervertebral discs persist