Eligibility

Inclusion Criteria:

1. ≥18 years old.
2. Requiring mechanical ventilation with actual or expected total duration of mechanical ventilation ≥ 48 hours.
3. Expected ICU stay ≥ 4 days after enrollment (to permit adequate exposure to the proposed intervention).

Exclusion Criteria:

1. >96 continuous hours of mechanical ventilation before enrollment.
2. Expected death or withdrawal of life-sustaining treatments within this hospitalization.
3. No expectation for any nutritional intake within the subsequent 72 hours.
4. Severe chronic liver disease (MELD score ≥20) or acute fulminant hepatitis.
5. Documented allergy to the amino acid intervention.
6. Metabolic disorders involving impaired nitrogen utilization
7. Not ambulating independently prior to illness that lead to ICU admission (use of gait aid permitted).
8. Pre-existing primary systemic neuromuscular disease (e.g. Guillain Barre).
9. Neuromuscular blocker infusion (eligible once infusion discontinued if other inclusion criteria met).
10. Intracranial or spinal process affecting motor function
11. Pre-existing cognitive impairment or language barrier that prohibits outcomes assessment.
12. Patients in hospital >5 days prior to ICU admission
13. Lower extremity impairments that prevent cycling (e.g. amputation, knee/hip injury).
14. Remaining intubated for airway protection only
15. Weight ≥150kg
16. Physician declines patient enrollment
17. Insufficient IV access
18. Pregnant
19. Incarcerated