Table 2 Inclusion and Exclusion Criteria {10}

1. Males and females, ages 15–30 years at enrollment

2. Able to understand and speak English (in order to appropriately follow the intervention)

3. Diagnosis of acute leukemia (myeloid, lymphoid) requiring allogeneic HCT

4. 6–24 months from allogeneic HCT

5. Females must have a negative urine/serum pregnancy test and must use an acceptable method of contraception, including abstinence, a barrier method (diaphragm or condom), Depo-Provera, or an oral contraceptive, for the duration of the study

6. Parental/guardian permission (informed consent) and if appropriate, child assent

1. Known sensitivity to NR

2. Concurrent use of any medications, including statins, likely to increase risk of NR toxicity {11d}

3. Active malignancy, investigational agent(s) within 4 wks, or systemic glucocorticoids within 12 wks

4. Currently meeting public health exercise guidelines

5. Use of NAD⁺ precursors (supra-physiologic) within 4 weeks

6. Hemoglobin < 10 g/dL

7. Platelets < 50 K

8. Diabetes Mellitus requiring insulin or insulin secretagogue

9. HbA1C ≥ 8%

10. Kidney disease (eGFR < 60 ml/min/1.73 m2)

11. Liver disease (ALT/AST > 3 × ULN)

12. Limitations in physical function preventing exercise testing/training

13. Contraindications to MRI

14. Unstable angina or history of acute myocardial infarction (< 5 days of planned study procedures)

15. Recurrent syncope

16. Symptomatic severe aortic stenosis

17. Uncontrolled arrhythmia causing symptoms

18. Pulmonary embolus < 3 months of study procedures

19. Thrombosis of lower extremities

20. Symptomatic moderate or severe persistent asthma based on FEV from pre-HCT pulmonary function testing

21. Room air desaturation at rest ≤ 85%

22. Females: Pregnant or planning pregnancy

23. Non-cardiopulmonary disorders that may affect exercise performance or be aggravated by exercise (e.g., infection, renal failure, thyrotoxicosis, > moderate GVHD resulting in physical or functional impairment)

24. Parents/guardians or subjects who, in the opinion of the Investigator, may be non-compliant with study schedules or procedures