Head-Down Bed-Rest Studies
Gravity FieldsCardiovascularMusculoskeletalNeuro-ophthalmicTerrestrial analogClinicianResearcherStudent
- 6° head-down tilt bed rest is the most common Earth analog for weightlessness, especially for bone, muscle and the heart. ◆◆◆◆ High · A
- It reproduces fluid shifts only partly, and doesn't model radiation. Thirty days of strict bed rest can cause optic disc swelling like SANS. ◆◆◆◇ Moderate · A
Proposed certainty (◆ High → ◇ Very low) and evidence-type tags: F flight · A analog · M model/animal · C computational · E expert/operational/standards. AI-proposed, pending reviewer confirmation. How to read the grades.
What it is
In head-down tilt bed rest (HDBR), healthy volunteers stay lying down with the head tilted 6° below the feet, usually for 30 days or more. Russian investigators pioneered the head-down tilt because it reproduces the headward fluid shift better than lying flat. It is now the most common Earth analog for weightlessness and for testing countermeasures for bone loss, muscle and heart atrophy, orthostatic intolerance and lost strength or exercise capacity [1].
What it shows
- Bed rest removes the usual pull of gravity from head to foot, shifts fluid toward the head, unloads the body, and reduces energy needs and sensory input [2].
- The fluid shift reduces plasma volume by 10–15% [2].
- NASA’s 70-day bed rest study ran eight integrated investigations on the same volunteers in a standardized bed-rest environment [3].
- SANS: after 30 days of strict head-down bed rest, volunteers developed optic disc swelling [4]. In a randomized crossover study, nightly lower body negative pressure reduced choroid swelling during bed rest [5].
What it misses
- Gravity still acts, just in a different direction. All Earth analogs have this problem [1].
- It is a poorer model for fluid shifts, spinal problems and radiation [1].
- Volunteers are confined and inactive, which brings in effects unrelated to weightlessness [2].
See Earth analogs for how bed rest compares with other analogs.
Evidence profile
- Overall certainty
- ◆◆◆◇ Moderate (proposed)
- Evidence types
- A · Terrestrial analog
- Literature through
- 2026-10-14
Requirements referenced 0
No NASA-STD-3001 requirement maps directly to this page. See the standards quick reference.
References 5
- Hargens AR, Vico L. Long-duration bed rest as an analog to microgravity. J Appl Physiol. 2016;120(8):891–903. doi:10.1152/japplphysiol.00935.2015 PMID:26893033 Peer-reviewed A
- Pavy-Le Traon A, et al. From space to Earth: advances in human physiology from 20 years of bed rest studies (1986–2006). Eur J Appl Physiol. 2007;101(2):143–194. doi:10.1007/s00421-007-0474-z PMID:17661073 Peer-reviewed A
- Cromwell RL, et al. Overview of the NASA 70-day bed rest study. Med Sci Sports Exerc. 2018;50(9):1909–1919. doi:10.1249/MSS.0000000000001617 PMID:29570535 Peer-reviewed A
- Laurie SS, et al. Optic disc edema after 30 days of strict head-down tilt bed rest. Ophthalmology. 2019;126(3):467–468. doi:10.1016/j.ophtha.2018.09.042 PMID:30308219 Peer-reviewed A
- Hearon CM Jr, et al. Effect of nightly lower body negative pressure on choroid engorgement in a model of spaceflight-associated neuro-ocular syndrome: a randomized crossover trial. JAMA Ophthalmol. 2022;140(1):59–65. doi:10.1001/jamaophthalmol.2021.5200 PMID:34882176 Peer-reviewed A
Machine-checked on 2026-10-14: each URL resolved, each DOI's title/journal/year matched via Crossref, and claims were checked against the source text (abstract or full NASA page). Human verification against full text is still required before review. NASA documents are U.S. Government works (public domain) and are summarized with attribution; journal articles are summarized, not reproduced.
Article info
- Authors
- Pending (AI-assisted draft)
- Reviewer
- Pending review
- Last reviewed
- Pending review
- Literature through
- 2026-10-14
- AI-assisted
- Yes (disclosed)
- COI
- Pending
- License
- CC BY-SA 4.0
- Use
- Educational only · Disclaimer
- Cite this version
- Pending first edition