Limited musculoskeletal benefits of artificial gravity combined with cycling during bed rest: Results from the BRACE study

Prolonged exposure to microgravity, simulated via 6° head‐down tilt bed rest (HDT), induces musculoskeletal deconditioning and negatively impacts body composition. This study evaluated whether a combination of aerobic exercise with artificial gravity (AG) offers superior protection in comparison to exercise alone. Twenty‐four healthy male participants completed 60 days of HDT, randomized into control (C), exercise‐only (EX) and exercise with AG (EX‐AG) groups. Muscle volume, intramuscular fat, body composition and isokinetic strength were assessed via whole‐body MRI and isokinetic dynamometry. All groups experienced thigh fat‐free muscle volume loss: C (10.5% ± 2.6%), EX (6.9% ± 2.4%) and EX‐AG (4.3% ± 2.4%), with EX‐AG showing significantly less atrophy than C ( p < 0.001). Compared with C, EX‐AG preserved more muscle in both anterior ( p < 0.001) and posterior ( p < 0.05) compartments, whilst EX preserved more muscle only anteriorly ( p < 0.05). The fat ratio increased more in C (8.9% ± 6.0%) compared with EX‐AG (−0.8% ± 3.8%; p < 0.05) but not EX (6.5% ± 9.8%). Muscle fat infiltration increased across all groups (C, 7.0% ± 3.7%; EX, 6.2% ± 4.3%; EX‐AG, 3.1% ± 4.7%) but was not different between groups ( p > 0.05). Maximal isokinetic torque decreased in all groups over all measured angular velocities but was not different between groups ( p > 0.05). This is the first study to investigate the combination of AG and exercise as a countermeasure to body composition changes induced by long‐term bed rest. We showed that EX‐AG provided partial protection against muscle atrophy and fat accumulation but did not outperform exercise alone in preserving muscle quality, strength or overall body composition.