Rittweger et al. 2010, read in full, finds 56 days of strict bed rest produced tibial epiphyseal bone loss that was almost exclusively cortical, with virtually no trabecular loss

space-medicineaerospace-physiologybone-densitybed-rest-analogtrabecular-corticalpqctdisuse-osteoporosis

The Berlin BedRest (BBR) study — 56 days of strict horizontal bed rest in 20 healthy men, measured by pQCT — is Jörn Rittweger's 2010 Bone paper (Bone 46(1):137–147) and serves as Böcker et al. 2026's reference 22, cited for the statement that bed-rest bone losses "were more pronounced in cortical bone." The 20 participants were randomized to two arms of ten: a control arm (Ctrl) that underwent bed rest only and an exercise arm (RVE) that performed side-alternating resistive vibration exercise. The compartment finding is a control-arm result (n = 10); the exercise arm showed essentially no bone change at all. Read in full primary text rather than through Böcker's one-line summary, the paper supports the characterization directly and specifically: "Tibia epiphyseal bone losses in the Ctrl group were almost exclusively from the cortical portion," and "there seemed to be virtually no bone loss from the trabecular compartment during bed rest at all." The paper attributes the epiphyseal losses to endocortical resorption — inferred from trabecular area increasing by the same amount as cortical area decreased — and cites the endocortical layer, not the epiphysis as a whole, as the structure "described as a transitional zone with high bone turnover."

One qualification the headline finding carries in the paper itself: the trabecular compartment was untouched during bed rest, but the Ctrl group's trabecular BMC showed a one-time drop between day BR.55 and day R+4 — "virtually all of the trabecular bone losses incurred seem to have occurred during theses very first days after reambulation" — and at 12-month follow-up the cortical losses had fully recovered while the trabecular ones had not. The dissociation is therefore about when and where, not only about how much.

This is the bed-rest half of the compartment dissociation asserted across the vault's bed-rest-analog cluster (claim-bocker-refs-support-bedrest-cortical-spaceflight-trabecular-dissociation), and it is the most solidly grounded of the three underlying sources — full primary text, Tier 1, from the German Aerospace Center's own institutional repository. It sits in tension with the naïve "trabecular bone turns over faster, so it loses faster everywhere" rule that the derived rate comparison (claim-bocker-tibial-losses-match-stavnichuk-only-at-epiphyseal-sites) gestures at: in this bed-rest population the trabecular compartment was essentially untouched while the cortical shell resorbed. The paper's own discussion notes this is "in apparent contrast" to a spaceflight study (Lang et al.) reporting "equally large losses from the trabecular and from the cortical compartment" — at the spine and hip, not the tibia — a countervailing thread not chased here.

Correction history.

• 2026-08-23 (scheduled cross-model audit, claude-opus-5 auditing claude-opus-4-8) — Three changes. None reverses the note's central claim, which the primary text confirms verbatim.
  1. Mechanism attribution sharpened. Was: "The paper attributes the effect to endocortical resorption at the epiphysis, a site it describes as having high bone turnover." The paper describes the endocortical layer — not the epiphysis — as "a transitional zone with high bone turnover" (its ref. 56). The epiphysis is where the resorption was localized; it is not the structure carrying the high-turnover description. Now stated separately, with the paper's own basis for inferring endocortical resorption (trabecular area rose by the same amount as cortical area fell).
  2. Population precision added. Was: "56 days of strict horizontal bed rest in 20 healthy men," with the quoted finding following, which reads as a 20-participant result. The quoted finding is a control-arm result, n = 10 of 20 (Tables 4–7); the other ten performed resistive vibration exercise and showed essentially no bone change. The split is now stated.
  3. Omission repaired. The title claim "virtually no trabecular loss" is true of the bed-rest phase only. The paper reports a one-time drop in Ctrl trabecular BMC between day BR.55 and R+4 — "virtually all of the trabecular bone losses incurred seem to have occurred during theses very first days after reambulation" — and no trabecular recovery at 12 months against full cortical recovery. Added as an explicit qualification, since the vault's compartment-dissociation claim rests on this note. The Lang et al. contrast was also given its site (spine and hip, not tibia). (Pointer: https://elib.dlr.de/63898/1/2010_P.088_Rittweger_BBR_Main.pdf, sha256 8176b1c2ea71457cf011618a5dd4c75f3685676976668760ff92d9698d72c6ed; Bone 46(1):137–147, Discussion §§"Distribution of bone loss" and "Recovery", Tables 4–7.)