Drinking one glass of beetroot juice won’t help older adults with a certain type of heart failure exercise better, even though it raises a chemical in their blood — they might need to drink it every day for a while before they see any benefit.

In older adults with HFpEF, compare submaximal aerobic endurance (e.g., time to fatigue on a cycle ergometer at 60% VO2 peak) after a single acute dose of beetroot juice (6.1 mmol nitrate) versus placebo, with plasma nitrite measured pre- and post-intervention, and washout period of ≥7 days between conditions.

Compare submaximal aerobic endurance and plasma nitrite levels in older adults with HFpEF after 4 weeks of daily beetroot juice (6.1 mmol nitrate) versus daily placebo, to test whether chronic exposure yields functional benefits absent after acute dosing.

Within the same individuals with HFpEF, compare the effect of a single acute dose of beetroot juice (6.1 mmol nitrate) versus 4 weeks of daily dosing on submaximal aerobic endurance and plasma nitrite to directly test the hypothesis that chronic exposure is required for benefit.

Correlate habitual dietary nitrate intake (via food diary and plasma nitrite) with submaximal aerobic endurance in older adults with HFpEF over 6 months to assess whether chronic exposure patterns predict functional outcomes.

Determine whether acute vs. chronic beetroot juice intake alters skeletal muscle mitochondrial efficiency or nitrate-nitrite-NO signaling pathways in older adults with HFpEF, to explain the lack of acute functional benefit.