Immune Cells During Disuse and Recovery

This is an interventional study enrolling healthy individuals aged 18-35 and 60-85 to understand the recovery of muscle health following a period of inactivity. The enrollment goal is 45 participants. The study will occur over the course of 1-2 months where participants will undergo testing before and after a 2-week limb immobilization period.

Visit 1 (Pre-testing)- After signing a consent form, participants will undergo a blood screening and an oral glucose tolerance test. After the visit, participants will be provided with a step activity monitor to track their level of activity. A dietary assessment will also be determined.

Visit 2- At a later time, the participant will return to the research center for a biopsy, blood draw, body composition scan, MRI and muscle strength testing.

2-week leg immobilization period- After visit 2 , the participant will return home and undergo a 14-day leg immobilization period using the equipment and instructions provided at visit 2.

Visit 3- During the limb immobilization period, participant will return to the research center for a single blood draw.

Visit 4- At the end of the 2-week limb immobilization period, the participant will return to the research center to undergo another biopsy, blood draw, body composition scan, MRI and muscle strength testing.

Visit 5- 2 days after the 2-week limb immobilization period, the participant will return for a biopsy and blood draw.

Visit 6- 7 days after the 2-week limb immobilization period, the participant will be asked to return for a final biopsy, blood draw, body composition scan, MRI and muscle strength testing.

Eligibility Criteria:
Inclusion Criteria:

1. Age between 18-35 and 60-85 yrs
2. Ability to sign informed consent
3. Free-living, prior to admission

Exclusion Criteria:

* History of cardiovascular disease (e.g., CHF, CAD, right-to-left shunt)
* History of endocrine or metabolic disease such as hypo/hyperthyroidism and diabetes
* History of kidney disease or failure
* Vascular disease
* Risk of DVT including family history of thrombophilia, DVT, pulmonary emboli, myeloproliferative diseases including polycythemia (Hb\>18 g/dL) or thrombocytosis (platelets\>400x103/mL), and connective tissue diseases (positive lupus anticoagulant), hyperhomocystinemia, deficiencies of factor V Leiden, proteins S and C, and antithrombine III
* Use of anticoagulant therapy (e.g., Coumadin, heparin)
* Elevated systolic pressure \>150 or a diastolic blood pressure \> 100
* Implanted electronic devices (e.g., pacemakers, electronic infusion pumps, stimulators)
* Cancer or history of successfully treated cancer (less than 1 year) other than basal cell carcinoma
* Currently on a weight-loss diet
* Chronic systemic corticosteroid use (≥ 2 weeks) within 4 weeks of enrollment and for study duration (intra-articular/topical/inhaled therapeutic or physiologic doses of corticosteroids are permitted)
* Androgens or growth hormone within 6 months of enrollment and for study duration (topical physiologic androgen replacement is permitted)
* History of stroke with motor disability
* A recent history (\<12 months) of GI bleed
* History of liver disease
* History of respiratory disease (acute upper respiratory infection, history of chronic lung disease)
* Pregnancy as determined by a pregnancy test
* Any staff members who report directly to an investigator or who report to someone who reports directly to an investigator.
* Any other condition or event considered exclusionary by the PI and faculty physician