Daily cycling exercise mitigates bedrest-induced deterioration in tibial cortical bone: Findings from cortical backscatter ultrasound in the BRACE RCT

Introduction: The objective of this study is to investigate whether a cycling exercise coupled with artificial gravity via a short-arm human centrifuge helps to prevent and / or reduce the deleterious effects induced by 60 days of anti-orthostatic bedrest. The effects of two different training schemes in comparison to no training on the intracortical pore morphology and viscoelastic properties were analyzed by means of quantitative cortical bone ultrasound.

Methods: The BRACE (Bed Rest with Artificial gravity and Cycling Exercise) study was conducted jointly by the CNES (Centre National D’Etudes Spatiales and ESA (European Space Agency) between April 2023 and July 2024 at the MEDES-IMPS (Institut Médecine Physiologie Spatiales) research facility in Toulouse, France. Ethical committee approval was obtained from the Ethics Committee Ile de France VI, Paris, France (no. 2022-A02074-39). Written informed consent was obtained from all participants in accordance with the Declaration of Helsinki. The project was organized in two campaigns of 88 days each, consisting of 14 days of baseline data collection (BDC-14 to BDC-1), 60 days of 6° Head Down Tilt Bed Rest (HDT1 to HDT60), and a 14-day recovery period (R+0 to R+13). 24 healthy male volunteers (age 20-45) were into 3 groups (G1: no training; G2: cycling exercise, G3: cycling and artificial gravity on a short-arm centrifuge). Ultrasound readings were performed using a POROUS R1C (Porous GmbH, Potsdam, Germany) device at 50% of the tibia lengths in the midshaft region of the left tibia in supine position at Baseline (BDC-8), during Bed Rest Phase (HDT30 and HDT60) and during the recovery phase (R+13). All measured parameters were normalized to the values measured at BDC-8. Two-way ANOVA was used to analyze the relative changes with respect to training and measurement time point ([Fig. 1]).

Fig. 1  Relative changes (mean and standard error) of the width of the intracortical pore size distribution (Full Width at Half Maximum) and the frequency-dependent attenuation during bedrest and 14-day recovery in untrained (group 1) and trained (groups 2and 3) participants.

Results: Distinct changes of intracortical pore morphology and viscoelastic attenuation were observed in the course of the trial. While no exercise resulted in continuous increases of mean (+15%, p=0.049), peak (+11%, p=0.07) , width (+35%, p=0.02) and 90% quantile (+13%, p=0.07) values of the pore size distribution, and increased porosity (+1%, p=0.04) as well as a loss of viscoelasticity (-0.06 dB/MHz/mm, 0.03) at R+13, both training types could maintain the initial properties during rest and recovery periods.

Discussion: 60-day bedrest increases pore size and reduces viscoelastic properties of cortical bone, which can be prevented by cycling training. Artificial gravity did not have an additional benefit compared to cycling alone. These microstructural and viscoelastic changes could be monitored non-invasively by means of cortical backscatter ultrasound.

Keywords: Bedrest, Ultrasound, Cortical Bone

Korrespondenzadresse: Kay Raum, Charité-Universitätsmedizin Berlin, Center for Biomedicine, Imaging, Simulation & Stimulation Lab, Hindenburgdamm 30a, 12203 Berlin, Deutschland, E-Mail: [e-mail]

 

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Conflict of interest

Inventor of the CortBS technology, shareholder and CSO of Porous GmbH

Publication History

Article published online:
21 March 2025