Aging-related functional declines are thought to be caused by hallmark biological processes that ultimately manifest in physical, mental, and metabolic impairments to compromise intrinsic capacity and healthspan. Exercise is the only multipotent treatment with promise to mitigate many of the aging hallmarks, but there is substantial variability in individual exercise responsiveness. Thus, the investigators approach to boosting exercise responsiveness in aging is to combine an exercise training prescription containing both endurance and resistance training (in alignment with DHHS guidelines) with a nitrate-enriched dietary supplement to augment the cellular, tissue, and systemic adaptations that induce myriad health benefits of exercise in older adults.

Aging-related declines in health and intrinsic capacity are linked to biological processes profoundly affecting all organ systems and tissues including skeletal muscle. Exercise is a multipotent countermeasure to these processes. However, there is significant inter-individual response heterogeneity (IRH) in the magnitude of exercise-induced health benefits. Boosting exercise responsiveness among older adults is thus a top priority. The investigators have found in older adults that supplementation with nitric oxide (NO) precursors nitrate and nitrite is safe, well tolerated, and improves: (i) physical performance; (ii) vascular endothelial function; (iii) mitochondrial function; (iv) oxidative stress; and (v) muscle inflammation. The investigators suspect deficits among some older adults in nitrate bioavailability and/or exercise-induced NO production may in part drive suboptimal exercise responsiveness. Given the powerful and sustaining impact of exercise-induced health benefits on morbidity and mortality, the investigator's fundamental premise is that exercise responsiveness of every older adult should be maximized. In the BOOST-X Trial the investigators will determine if increasing nitrate bioavailability via dietary supplementation is an efficacious approach to more older adults attaining these essential health benefits. Low cardiorespiratory fitness (CRF, VO2max) and low functional muscle quality (fMQ; strength/muscle mass) are multi-system manifestations of degenerative aging that include vascular endothelial and mitochondrial dysfunction, oxidative stress, and inflammation. CRF and fMQ are modifiable with endurance (ET) and resistance (RT) training. This planned trial will be the first to evaluate the efficacy of coupling a nitrate-rich nutritional supplement with a combined ET+RT prescription in line with DHHS weekly exercise guidelines. The investigators will test the central hypothesis that daily nitrate supplementation will augment exercise training-induced gains in CRF and fMQ accompanied by improvements in vascular endothelial and mitochondrial function. Aim 1: Assess the clinical impact of nitrate supplementation on the proportion of older adults attaining exercise-induced health benefits. N=226 participants stratified by sex and age group (60-69 vs ≥70 y) with random assignment to nitrate (400 mg, 2x/day) (n=113) vs. placebo (nitratedepleted) (n=113) during 12 wk of 3x/wk ET+RT. 1˚ Outcomes: MCID attainment for CRF and fMQ. Expected Results: Daily nitrate will reduce the proportion of older adults not attaining CRF and fMQ MCIDs by a full 1/3. Aim 2: Assess potential mechanisms underpinning adaptations to exercise +/- nitrate supplementation. The investigators will test/integrate in vivo, ex vivo, in vitro and molecular mapping assays considered central to exercise +/- nitrate adaptations and leverage a multidimensional learning framework to better understand the biocircuitry underpinning MCID attainment. 1˚ Outcomes: Vascular endothelial function, muscle mitochondrial function. Expected Results: MCID attainment will be closely linked to improvements in vascular endothelial function and muscle mitochondrial function. The acute molecular responses to exercise will be differentially regulated by nitrate supplementation, and the novel biocircuitry will reveal key features that influence adaptability.

Inclusion Criteria:

1. Male or female aged 60 years or older
2. Free of chronic disease or disorder that would preclude full participation or have the potential to confound results
3. No structured exercise program (2 or more bouts/wk) within previous 12 months
4. Cognitively capable of providing informed consent

Exclusion Criteria:

1. BMI ≥ 30.0 kg/m2

2. Neurodegenerative disease

3. Neuromuscular, musculoskeletal or orthopedic disorder or condition that would limit ability to perform the exercise prescription and/or physical performance testing

4. Diagnosed orthostatic hypotension, i.e., a drop in systolic blood pressure of at least 20 mmHg or a drop in diastolic blood pressure of at least 10 mmHg within three minutes of standing up from a sitting or lying position.

5. Resting blood pressure <90/60 mmHg or >160/95 mmHg

6. Uncontrolled hypertension

7. Any current cardiovascular disease or cardiopulmonary instability

8. Recent cardiovascular event or procedure within the preceding 6 months

   1. If valve replacement has been performed, patient may not be enrolled for 12 months after the procedure
   2. Any mechanical valve replacement that requires continuous warfarin anti-coagulation

9. Anemia: Hgb <11.0 (♂),10.0 (♂) gm/dl

10. Diabetes with HgbA1c >7.0% or fasting blood glucose ≥ 130 mg/dl

11. Liver disease with ALT > 52 U/l)

12. Chronic kidney disease (eGFR < 45)

13. Any current infectious disease

14. Any other disease or disorder that could influence exercise response, preclude full participation or have the potential to confound results (e.g., chronic lung disease, cognitive impairment, current cancer diagnosis or within 2 yr remission, cerebrovascular disease, pain)

15. Life expectancy < 1 year Medications / lifestyle

16. Insulin sensitizing/blood glucose lowering agents such as metformin

17. Currently on or have used GLP-1 agonist or other metabolic / weight loss drug in previous 12 weeks

18. Use of nitrate medications

19. High dose statin (≥40 mg/d simvastatin equivalence)

20. Chronic corticosteroids

21. Testosterone or other anabolic/androgenic hormone therapy

22. Lidocaine allergy

23. Regular tobacco use and/or vaping > 1/wk

24. Use of cannabis > 1/wk

25. Excessive alcohol consumption (3 drinks/d or 7 drinks/wk for females; 4 drinks/d or 14 drinks/wk for males)

26. Use of illicit drugs (e.g., cocaine, opioids)

27. Unable to commit to ~4 months required to complete the study

De-identified phenotyping data will be made accessible through supplementary data tables and files alongside manuscript publication or via third-party repositories. This data will also be hosted on secure server space without any link to PHI and made accessible through a publicly available Shiny app. Primary cell aliquots and biobanked snap frozen muscle and/or frozen blood samples will be provided to investigators upon reasonable request along with de-identified metadata.

Data share will begin when as soon as first data collections begin. Sub award sites will enter participant data on the secure Data Entry Management System (DEMS). Data shares will continue until the close of study.

Access to all study data is granted on the researcher regulatory training and local IRB approval.

Participants will be randomized in double-blind fashion to consume 2x/day nitrate-rich beetroot juice (Beet-it®, 400 mg inorganic nitrate per dose x 2/day) or nitrate-depleted placebo beetroot juice. To bolster trial rigor, the placebo is also produced by Beet-it®, is taste- and volume-matched, contains all other potentially bioactive ingredients sans nitrate, and active vs. placebo bottles are indistinguishable. The blind will be held by independent research staff not involved in the study. Daily consumption of each dose will be closely monitored via a phone-based logging app integrated with the electronic DEMS. The app also enables research staff to push reminders to participants as needed. Participant tolerance has not been a concern in our prior and ongoing studies. However, the investigators will monitor individual tolerance and address any issues on a case-by-case basis.