Physical activity appears to be an important lifestyle habit to achieve healthy aging by promoting autonomy and quality of life. Interestingly, the dramatic changes that the human body undergoes due to bedrest for illnesses and hospitalization are similar to those seen over decades of normal aging. Bedrest in otherwise healthy older individuals can lead to a reduction of muscle size and strength, changes in bone strength and function of the heart and blood vessels. Bedrest can also lead to changes in keeping proper balance as well as changes in processing and understanding information. All of these factors negatively affect activities of daily living leading to physical function impairment and development of frailty, a clinical condition associated with an increased risk for disease and death.

The purpose of this study is to investigate whether exercise can counteract the negative effects of 2-week head tilt down bed rest on muscle function and metabolism, postural control, bone structure, orthostatic tolerance and cognitive function in adults.

For this study the investigators will recruit 24 healthy men and women between 55 - 65 years of age. All subjects will spend a total of 26 days (5 days of adaption period, 14 days of bed rest with 6 degrees of downward inclination, and 7 days of recovery period) at the McGill University Health Centre (MUHC). During this study, 12 subjects will randomly undergo an exercise intervention as countermeasure during the 14 days of bed rest period and 12 will serve as control.

Each subjects participation in this study will involve 1 telephone call (pre-screening) and 4 visits at the MUHC: 1 screening visit (Visit 1) followed by a 26-day long visit (Visit 2) and 2 follow-up visits (Visit 3 and Visit 4). During Visits 2 - 4 various measurements will be performed to assess sensorimotor control, muscle function and metabolism, bone structure, cardiovascular function, cognitive performance and function, and specimen collection (blood, urine, saliva, feces and muscle tissue).

Inclusion Criteria:

• A minimum of 20 and a maximum of 24 non-smoking participants in the age group of 55 to 65 years old, half male and half female.
• Female participants must be menopausal (no menses for at least 1 year (or documented ovariectomy) and a serum FSH above 30 IU/L).
• Height between 158 to 190 cm with a body mass index between 20 to 30 kg/m2.
• Physically and mentally healthy subjects that will have successfully passed the psychological and medical screening appropriate for the age group.
• Participation in at least 2.5 hours of exercise at a moderate to vigorous-intensity aerobic activity per week.
• Willing to be assigned randomly either to the exercise or the control group.

Exclusion Criteria:

• Participants must be dementia-free, drug- or alcohol-addiction free, with no history of heart attacks, no thrombosis risk, no severe allergies, no hypocalcaemia, no uric acidemia, no orthostatic intolerance, no vestibular disorders, no considerable musculoskeletal issues, no chronic back pain, no head trauma, no seizures, no ulcers, no renal stones, no gastro-esophageal reflux disease or renal function disorder, no hiatus hernia, no migraines, and no mental illness.
• Electrocardiogram abnormalities
• Anemia
• Low bone mineral density
• Medication requirements that may interfere with the interpretation of the results
• Recent substandard nutritional status
• Claustrophobia
• Special dietary requests (e.g. vegetarian, vegan or some other diet)
• Sedentary people and people that are addicted to exercise
• Metallic implants (pacemakers, ICDs, CRT devices, infusion pumps, cerebral artery aneurysm clips, dental implants, tissue expander etc.), osteosynthesis material
• Given blood in the past 3 months before the onset of the experiment
• Smoked (tobacco and/or marijuana (THC)) within 6 months prior to the start of the study
• Abused drugs, medicine or alcohol within up to 30 days prior to the start of the study
• Participated in another study within 2 months before study onset