The purpose of this small pilot study is to refine a combined intervention of IV amino acids and cycle ergometry in critically ill patients, and to gather preliminary data, before proceeding with a larger multi-center RCT. A total of 10 patients will receive the combined intervention.

Inclusion Criteria:

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

Exclusion Criteria:

1. >120 continuous hours of mechanical ventilation or HFNC before enrollment
2. Expected death or withdrawal of life-sustaining treatments within 7 days from enrollment
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. Not ambulating independently prior to ICU admission (use of gait aid permitted)
7. Pre-existing primary systemic neuromuscular disease (e.g. Guillain Barre)
8. Neuromuscular blocker infusion (eligible once infusion discontinued if other inclusion criteria met)
9. Pre-existing intracranial or spinal process affecting motor function
10. Pre-existing cognitive impairment or language barrier that prohibits outcomes assessment
11. Lower extremity impairments that prevent cycling (e.g. amputation, knee/hip injury)
12. Weight >150kg
13. Pregnant
14. Incarcerated