An interventional study of head down bedrest and caloric restriction in Microgravity and Caloric Restriction, sponsored by Centre National d'Etudes Spatiales. Active, not recruiting at 1 site in France. Open to male participants aged 20 Years to 40 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-07-10.
Sponsored by Centre National d'Etudes Spatiales · Not applicable, Interventional, and Other
The goal of this single arm, interventional monocentric clinical trial is to investigate the physiological effects of a combination of head-down bedrest and caloric restriction on the human body. A set of measurements will assess the changes in the musculoskeletal, cardiovascular, hematological, immune, neurological, cognitive and metabolic systems, in 10 healthy male volunteers.
The main question it aims to answer is: what are the physiological responses to fasting in a microgravity environment?
In an exploratory study such as this one, where many physiological systems are explored, it is difficult to select a single important endpoint. However, given the known effect of both caloric restriction and head-down bedrest on muscle loss, and its critical importance for the success of space missions, lean body mass, as assessed by DEXA, was chosen as the primary endpoint.
The secondary endpoints are:
Participants will be exposed to a microgravity analog model (head down bed rest) and controled caloric restriction environment for 10 days, multiple physiological assessments will be performed during this period. Followed by a rehab period before leaving the study.
Centre National d'Etudes Spatiales is the lead sponsor of 10 studies on the registry; none are open to participants now.
Counted across the registry records on this site, refreshed daily.
Exclusion Criteria:
head down bedrest and caloric restriction (250 kcal/day)
Other: head down bedrest and caloric restriction
the intervention is 10 days of head down bedrest (-6°) and controlled and progressive caloric restriction, then controlled and progressive refeeding
Lean Body Mass
Lean Body Mass assessed by dual energy x-ray absorptiometry (DEXA)
Time frame: At baseline, during the ten days of intervention and until 90 days after the end of the intervention
Change in body fluid compartments by bioelectrical impedance analysis
Extracellular, intracellular and total body water (L) will be estimated by bioimpedance
Time frame: At baseline, during the ten days of intervention and until 90 days after the end of the intervention
Change in whole-body Magnetic Resonance Imaging (MRI)
Change in MRI-measured whole-body Lean mass (kg) and Fat mass (kg) will be estimated
Time frame: At baseline and at day 9 of intervention period
Change in mood
Change in mood is assessed using the Profile of Mood States (POMS) questionnaire. POMS questionnaire gives 6 measures of mood: Tension/anxiety, Depression, Anger/hostility Dynamism, Fatigue, Confusion A Total Mood Disturbance (TMD) score is calculated by summing the totals for the negative subscales (tension, depression, fatigue, confusion, anger) and then subtracting the totals for the positive subscale (vigor /esteem-related affect).
Time frame: At baseline, during the ten days of intervention and until 4 days after the end of the intervention
Assessment of movements by volunteers
Actigraphs attached to wristbands placed on the non-dominant wrist and ankle of each volunteer
Time frame: At baseline, during the ten days of the intervention and until 4 days after the end of the intervention
Change in cardiovascular deconditioning and orthostatic tolerance (stand test)
This test continuously measures heart rate (bpm) via a Finapres device while subjects sit for 5 minutes, then stand for 10 minutes and then sit again for 5 minutes
Time frame: At baseline and 1 day after the end of intervention period
Changes in orthostatic tolerance
Orthostatic tolerance will be assessed during a tilt test combined with Lower Body Negative Pressure test (LBNP test)
Time frame: At baseline and 1 day after the end of intervention period
Changes in peak aerobic power (VO2max test)
Exercise capacity wil be assessed by graded cycling on sitting ergometer until exhaustion
Time frame: At baseline and 4 days after the end of intervention period
Changes in plasma volume
Plasma volume (L) will be assessed by the Dill \& Costill method
Time frame: At baseline, during the ten days of the intervention and until 4 days after the end of the intervention
Change in long term blood pressure
This test continuously measures Blood Pressure during 24 hours with the SOMNOTouch device.
Time frame: At baseline, during the 10 days of the intervention, and 4 days after the end of the intervention
Change in macrocirculation
Macrocirculation will be assessed using standard ultrasound measurements at the carotid and femoral levels (arteries and veins).
Time frame: At baseline, during the 10 days of the intervention, and at 3 days after the end of the intervention
Change in endothelial function
The tests consists in the measurement of the variations of the brachial artery diameter as a response to shear stress.
Time frame: At baseline, during the 10 days of the intervention, and 3 days after the end of the intervention
Myofiber atrophy evaluation
Biopsy sampling from m. vastus lateralis will be performed to measure structure and function of muscle fibers.
Time frame: At baseline and at day 9 of intervention
Changes in jump performance
Jump performance will be assessed on a platform and height of the jump will be evaluated
Time frame: At baseline and 1 day after the end of the intervention
Change in protein metabolism
Labeled tracers (¹³C leucine for oxidation, ¹⁵N-phenylalanine for degradation, ²H₅-phenylalanine for synthesis monitoring and NaH13CO3 for quantification of amin acid oxidation) will be infused to the volunteers, and blood, urine, muscle and breath samples will be collected.
Time frame: At baseline and at day 9 of the intervention
Change in muscle strength
Muscle strength will be assessed via dynamometry
Time frame: At baseline and 2 days after the end of the intervention
Change in bone biological marker
Measuring bone-specific Alkaline Phosphatase (bAP) in blood
Time frame: At baseline, during the ten days of intervention and until 90 days after the end of the intervention
Changes in bone density (by High Resolution Peripheral Computed Tomography (HR-pQCT))
Bone density (g/cm2) is measured at tibia and radius level with HR-pQCT.
Time frame: At baseline and until 90 days after the end of the intervention
Changes in Resting Metabolic Rate (RMR)
RMR will be measured by indirect calorimetry technique
Time frame: At baseline, during the ten days of intervention and until 90 days after the end of the intervention
Change in nitrogen balance
Nitrogen balance is a measure of nitrogen input minus nitrogen output. Nitrogen intake is calculated with a nutrition software. Protein oxidation measured in the 24-Hour urine collection estimates nitrogen output.
Time frame: At baseline, during the ten days of intervention and at 90 days after the end of the intervention
Change in metabolic flexibility (Oral Glucose Tolerance Test (OGTT))
Metabolic flexibility will be measured during OGTT to assess the ability of the body to adjust energy substates' availability.
Time frame: At baseline and 4 days after the end of the intervention.
Change in glucose homeostasis
Continuous measurement of interstitial glucose concentration by Dexcom sensor
Time frame: From baseline to day 5 after the end of the intervention
Change in energy expenditure of tissues and organs (by PET-scan)
Regional mapping of metabolic activity by dynamic PET-scan with ¹⁸F-fluorodeoxyglucose
Time frame: At baseline and at day 7 of the intervention period
Metabolic change in adipose tissue
Histology, cell culture, adipocyte size distribution and whole adipose tissue transcriptome, proteome, lipidome and metabolome on adipose tissue biopsy
Time frame: At baseline and at day 9 of the intervention
Change in gut microbiota
Gut microbiome, metabolome and proteome will be measured in stool samples
Time frame: At baseline, during the ten days of the intervention and 4 days after the end of the intervention period
Modification of self perceived hunger
Questionnaires about self-perceived hunger will be delivered before and after breakfast, lunch, snack, and dinner, or at the equivalent times on the fasting days. The questionnaire consists of a Visual Analogue Scale on which the volunteer must indicate their level of hunger (from 'not at all' to 'extremely')
Time frame: At baseline, during the ten days of the intervention and until 4 days after the end of the intervention period
Change in energy requirements
Change in energy requirements using water labeled with a stable oxygen isotope (H218O)
Time frame: At baseline and at day 9 of the intervention period
Change in motor function (Sit-to-stand test)
Sit-to-stand test : volunteer will be requested to rise as fast as possible from a chair without using hands and stand for 10s. The following parameter will be measured : Settling time after standing.
Time frame: At baseline and 1 day after the end of the intervention period
Change in standing balance
This test assesses standing balance on a platform covered with 12-cm thick medium density foam.
Time frame: At baseline and 1 day after the end of the intervention period
Change in vestibular health
Battery of tests will be used to asses vestibular health: recovery from fall, path integration, distance perception, perception of self-rotation, how long 1', Posner task, antisaccade task
Time frame: At baseline and 1 day after the end of the intervention period
Change in cognitive state
This test monitor changes in the subject's emotional state and executive function by evaluatingpsychotechnical tasks on a laptop (the neurosensorybox) with physiological sensors (SOMNO HD system).
Time frame: At baseline, during the ten days of the intervention period and at day 5 after the end of the intervention
Salivary cortisol evolution
To characterize stress level, morning and evening salivary cortisol (ng/ml) will be assessed
Time frame: At baseline, at day 1, 3 & 10 of intervention period, and day 4 after the end of the intervention
Change in memory performance
Subjects are exposed to a series of images that will have to be remembered. After a delay of 1 hour or 24 hours they will be questioned on a series of images presented under the same conditions and they will have to indicate in a grid whether these images are known or new
Time frame: At baseline, during the ten days of the intervention period, and until 3 days after the end of the intervention
Change in the internal representation of 3D space
This tests consist in a rhythmic point-to-point hand movements in virtual reality.
Time frame: At baseline, during the ten days of the intervention period, and until 3 days after the end of the intervention
Change in gastro-brain interaction
Assessment of the correlation between gastric electrical activity (measured via Electrogastrography) and neural oscillatory responses (measured via Electroencephalography) during a cognitive task
Time frame: At baseline, during the ten days of the intervention period, and until 4 days after the end of the intervention
Change in motor function (Walk and turn test)
Walk and turn test : volunteer will be instructed to walk as quickly as possible straight ahead toward a cone walk around it and return to the chair. Completion time per walk-and-turn trial will be measured.
Time frame: At baseline and 1 day after the end of the intervention period
Change in motor function (Tandem Walk)
Tandem walk : Volunteer will walk 10 heel-to-toe steps with their arms folded across their chests and their eyes closed (3 trials) followed by one trial with their eyes open. Percentage of correct steps will be measured.
Time frame: At baseline and 1 day after the end of the intervention period
Plan to share: No
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