A 60 Days Head Down Tilt Bedrest With Artificial Gravity and Cycling Exercise on 24 Healthy Male (BRACE)

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 secondary objective is to investigate whether the combination of a supine cycling exercise with artificial gravity is more effective than the same supine cycling exercise alone in preventing or reducing the effects of head-down bedrest. During a randomized, 60 day bed rest study, in 24 healthy male adults, the two following aims will be undertaken: * Fourteen scientific protocols will assess the changes in the cardiovascular, metabolic, musculoskeletal, neuro-sensorial, haematological, and immunological systems. * In the above-mentioned systems, the comparative potential beneficial effects of the two countermeasure protocols will also be investigated by the scientific protocols and bedrest standard measurements (BSM).

Inclusion Criteria: * Healthy male volunteer (see below the description of medical tests and laboratory analysis performed at the selection visit) * Aged 20 to 45 years * No overweight nor excessive thinness with BMI (weight kg/ height m2) between 20 and 27 kg/m2 * Height between 158 and 190 cm * Certified as healthy by a comprehensive clinical assessment (detailed medical history and complete physical examination): in particular, free from any chronic disease or any acute infectious disease or cardiovascular, neurological, of the ear, nose, throat (especially orthostatic hypotension and vestibular disorders), orthopaedic or musculoskeletal disorders * Good mental health: tests and psychological interview will be held by a specialist in extreme environment * Fitness level assessment: 35 mL/min/kg \< VO2max \< 55 mL/min/kg * Non active smokers * No alcohol or drug dependence, and no medical treatment * Covered by a Health Insurance System * Having signed the information consent * Free of any engagement during the study Exclusion Criteria: * Any history or presence of clinically relevant cardiovascular, neurological or ear, nose, throat disease, any chronic disease; any acute infectious disease. Particularly: * Symptomatic orthostatic hypotension whatever the decrease in blood pressure, or asymptomatic postural hypotension defined by a decrease in systolic blood pressure equal to or greater than 20 mmHg within 3 minutes when changing from the supine to the standing position, * Cardiac rhythm disorders, * Hypertension, * Chronic back pains, * Vertebral fracture, scoliosis, or herniated disc, * Glaucoma, * Self-reported hearing problems, * Vestibular disorders * History of migraines, * History of hiatus hernia or gastro-esophageal reflux, * History of thyroid dysfunction, renal stones, diabetes, * History of head trauma, * Abnormal result for lower limbs echo-doppler, * History of genetic muscle and bone diseases of any kind, * Past records of thrombophlebitis, family history of thrombosis or positive response in thrombosis screening procedure (anti thrombin III, S-protein, C-protein, factor V Leiden mutation and the mutation 20210 of the prothrombin gene), * Bone mineral density: T-score ≤ -1.5, * Poor tolerance to blood sampling, * Having given whole blood (more than 7 mL/kg) in a period of 8 weeks or less before the start of the experiment, or having given whole blood more than 2 times in the past year, * Significant history of allergy, especially no dermatological or food allergy, * Significant anomaly detected in the biological analysis, * Positive reaction to any of the following tests: hepatitis A immunoglobulin, hepatitis B antigen, anti hepatitis C antibodies, anti Human Immunodeficiency Virus 1+2 antibodies, * Vegetarian or vegan, * Refusal to give permission to contact his general practitioner, * Subject who, in the judgment of the investigator, is likely to be non-compliant during the study, or unable to cooperate because of a language problem or poor mental development, * Subject already participating or in the exclusion period of a clinical research, * Subject who has received more than 4500 Euros within 12 months for being a research subject, * Subject who cannot be contacted in case of emergency, * Subject who had the two knees injured * MRI contraindications * History or active claustrophobia * Osteosynthesis material, presence of metallic implants or any other contra-indication for MRI * Vulnerable persons according to French law (L1121-5 to L1121-8) : * Persons deprived of their liberty by an administrative or judicial decision * Persons under involuntary psychiatric care * Persons admitted in a health or social establishment for purposes other than research * Minors * Adults subject to legal protection (subject under guardianship or trusteeship) or unable to express their consent