Impact of beet juice on leg blood flow capacity at rest and during passive movement in older adults

The study will use a placebo controlled, cross-over design to determine if beet juice can increase leg blood flow and femoral artery dilation for older adults. The study will be conducted in the Exercise Science Research Laboratory at the University of the Sunshine Coast. After expressing interest in participating, all potential participants will attend an initial visit (visit 1, 60 min) to screen them against inclusion/exclusion criteria, clarify experiment details, ensure written informed consent, and to familiarise participants with the study procedures. During this visit, participants will have the opportunity to practice and become familiar with passive leg movement, ensuring appropriate muscle relaxation. Participants will then attend two experimental visits (visits 2 and 3) which will be approximately 6 hours each, separated by at least 3, but no more than 14 days. During these visits, participants will have blood pressure measured and then a blood sample will be taken for measurement of circulating nitrate (NO3-) and nitrite (NO2-). Baseline arterial stiffness, femoral artery dilation capacity (flow mediated dilatation), femoral artery blood flow (reactive hyperaemia), and blood flow during passive leg movement will be measured before the participant consumes 140 ml of concentrated beet juice or the placebo (nitrate-depleted beet juice). The beet juice and placebo taste, smell, and look the same and will be given in random order. Participants will then have a waiting period of 2 hours, which is the duration required for NO3- supplementation to significantly elevate plasma NO2- (ie the window of peak physiological effect). During this waiting period, participants will be asked to complete a medical history questionnaire (which includes smoking history and medication use) and a habitual physical activity questionnaire, Participants will be given a standardised low-nitrate meal and water and they will be free to talk, read, watch television, or undertake a sedentary activity of their choice. After the 2-hour waiting period, all baseline measurements will be repeated: blood pressure and a blood sample for NO3-/NO2- measurement, and then arterial stiffness, flow mediated dilatation, reactive hyperaemia and blood flow during passive leg movement.