Effect of artificial gravity on calcaneal bone marrow adipose tissue and mineral content in female and male participants in 60 days of bed rest.

In 30 seconds

This prospective randomized controlled trial examined calcaneal bone marrow adipose tissue (BMAT), bone mineral density (BMD) and foot pain during 60 days of head-down-tilt bed rest in 16 men and 8 women assigned to control, continuous artificial gravity or intermittent artificial gravity. After bed rest, 83% reported foot pain. Calcaneal BMAT did not change significantly, while BMD was reduced at reambulation days 3 and 11 (-0.05 ± 0.06 and -0.06 ± 0.12 g/cm², respectively). Neither artificial-gravity intervention significantly altered BMAT or BMD; sex-based analyses found BMD loss in men but not women.

Key findings

• After bed rest, 83% of participants reported foot pain.
• Calcaneal BMAT changes were not significant: control, +0.2% ± 0.8%; continuous artificial gravity, +0.5% ± 1.1%; intermittent artificial gravity, +0.1% ± 1.5% (P = 0.368).
• Calcaneal BMD fell at reambulation days 3 and 11 (-0.05 ± 0.06 and -0.06 ± 0.12 g/cm²; P = 0.008 and P = 0.020); artificial gravity did not significantly alter BMD.
• Sex-based analyses showed calcaneal BMD loss in men but not women; BMAT and BMD were inversely correlated in both groups.

Why it matters

The findings indicate that prolonged inactivity can be accompanied by foot pain and calcaneal demineralization even when BMAT does not measurably increase. The observed BMD reduction after reambulation and lack of significant benefit from the tested artificial-gravity regimens are relevant to understanding bone changes during recovery from prolonged bed rest and return to activity after spaceflight.

What to keep in mind

The trial included 24 participants, and the findings concern a 60-day bed-rest model and calcaneal outcomes; applicability beyond this setting is uncertain.