The purpose of this study is to evaluate the changes of muscle, in microgravity. Which will help explain the health benefits of exercise. There are tests that can be done to tell researchers more about the human body, such as a dual energy x-ray absorptiometry (DEXA) scan, which measures body composition (fat and lean body mass). The use of muscle testing and a Handgrip test can tell us about the strength and power within an individual's muscles. A VO2 max test helps us understand the aerobic fitness level of an individual and one of the most important aspects of this study are muscle cells. A muscle biopsy allows us to obtain muscle cells from the thigh, which will be sent into space by a rocket. Researchers will study these muscle cells in a low gravity environment aboard the International Space Station. Studying the muscle cells under those conditions will potentially mimic an accelerated aging process, which will help researchers better understand muscle wasting in the elderly.

Inclusion Criteria:

• Participant is capable of giving informed consent and has voluntarily signed and dated an informed consent form, approved by an Institutional Review Board and provided Health Insurance Portability and Accountability Act authorization (HIPAA) or other privacy authorization prior to any participation in study.
• Participant is 20-40 or 60-80 years of age, inclusive
• Participant BMI <30 kg/m2
• Participant states willingness to follow protocol as described, including the prescribed activity level and completing any forms needed throughout the study.

Exclusion Criteria:

• Participant reports a history of type 1 or type 2 Diabetes; or Hgb A1c > 6.5% at screening visit.
• Participant is actively pursuing weight loss and/or lifestyle changes.
• Participant has a history of pressure ulcers.
• Participant has a stated history of Deep Vein Thrombosis (DVT), recent (within last 3 months) pulmonary embolism, or has a positive D-dimer test and lower extremity ultrasound at screening, or a known hypercoagulable condition, or other clotting or bleeding disorders.
• Participant has poorly controlled hypertension or hypotension in the opinion of the study PI or medical investigator (MI).
• Participant has untreated hypothyroidism or hyperthyroidism.
• Participant has current infection (requiring prescription antimicrobial or antiviral medication, or hospitalization), or corticosteroid treatment (with the exception of inhaled or topical steroids) in the last 3 months prior to screening visit.
• Participant is currently taking prescription strength anti-inflammatory medication or has taken prescription strength anti-inflammatory medication in the 6 weeks prior to screening.
• Participant has had surgery requiring >2 days of hospitalization in the last 3 weeks prior to screening visit.
• Participant has an active malignancy or autoimmune disease.
• Participant has current significantly impaired liver function in the opinion of the study PI (mild asymptomatic fatty liver is acceptable), or hepatic enzyme tests are ≥2.5 times normal limit.
• Participant has a chronic, contagious, infectious disease, such as active tuberculosis, Hepatitis B or C, or HIV, per self-report.
• Participant is an amputee and/or has presence of partial or full artificial limb.
• Participant has had a significant cardiovascular event (e.g. myocardial infarction, stroke) ≤ 6 months prior to screening visit; or stated history of congestive heart failure; or participant has evidence of cardiovascular disease assessed during the ECG at screening.
• Participant has a history of, or currently has uncontrolled severe diarrhea, nausea or vomiting.
• Participant has an obstruction of the gastrointestinal tract, inflammatory bowel disease, short bowel syndrome or other forms of gastrointestinal disease such as stage III or above gastroesophageal reflux disease, gastroparesis, peptic ulcer disease, celiac disease, intestinal dysmotility, diverticulitis, ischemic colitis.
• Participant has used tobacco within the last 3 months.
• Participant has a history of drug or alcohol abuse (> 3 drinks per day) within the last 5 years
• Female participant is pregnant, lactating or is within 6 weeks postpartum prior to the screening visit
• Participant has impaired renal function: estimated glomerular filtration rate (eGFR) ≤ 50 ml/min/1.73m2 determined at screening.
• Participant's triglyceride level is ≥ 250 mg/dl and LDL cholesterol is > 150 mg/dl at screening.
• Participant has a urine albumin-to-creatinine ratio (UACR) ≥300 mg/g at screening in a single urine specimen (per National Kidney Foundation guideline).

Males and females in the age ranges 20-40 and 60-80 years were recruited. Participants were medically screened to determine good health, weight stable (less than 3kg weight change during the previous 6 months), and without any contraindication to exercise. Approximately equal numbers of men and women were be recruited. Neither race nor ethnicity were exclusions.