Effects of Isotonic Beetroot Supplementation on Sprint Interval Exercise Performance

This study aims to examine the effects of dietary nitrate supplementation via beetroot juice on sprint interval cycling exercise performance. Twenty-four participants (male or female) will undertake a randomized, crossover trial where they consume either (i) an isotonic beetroot juice drink containing nitrate (12.9 mmol) for 5 days or (ii) an isotonic sports drink (no nitrate) for 5 days. Drinks will be equivalent in isotonicity and colored the same so that participants and investigators will be blinded to each trial. Randomization and drink allocation will be completed by a third person not associated with the study team. On Day 5 of each trial, participants will come to the laboratory and 2 hours after consuming their allocated drink will complete a 6 bouts of sprint interval exercise (10 second all-out maximal sprints interspersed with 50 seconds rest). Power output (peak and mean) during cycling sprints will be measured as the primary outcome measure. Salivary measures of nitrate/nitrite will be taken at three time points over the course of the morning on Day 5 - (i) pre-drink consumption; (ii) 2 hours post-drink consumption; and (iii) post-exercise. Plasma measures of nitrate and nitrite will be taken at two time points over the course of the morning on Day 5 - (i) pre-drink consumption; and (ii) 2 hours post-drink consumption. Near infra-red spectroscopy (NIRS) will be used to measure muscle (vastus lateralis) oxygenation during cycling bouts. A Stroop test to measure inhibition (executive function) will be taken pre- and post-exercise. Sensory perception of the drink will be measured immediately post-consumption on Day 5. After a 5-day washout period participants will crossover and begin their second trial.

Inclusion criteria

• Age: 21 - 40 years
• Healthy and injury-free (e.g., no cardiovascular disease, diabetes mellitus, orthopaedic impairment that interferes with moderate-to-vigorous exercise)
• Blood pressure < 130/90 mmHg
• Be physically active: Engaging in a minimum of 150 minutes of moderate-intensity exercise or 75 minutes of vigorous-intensity physical activity each week.
• Recreational cyclist (Minimum 1 hour cycling per week).
• Body mass index: 18.5-25 kg/m2
• Non-smoker
• Asian

Exclusion criteria

• Any allergies to beetroot or isotonic drink.
• Asthma
• Any diagnosed form of cardiometabolic disease (heart disease, stroke, peripheral vascular disease, diabetes, metabolic syndrome, high blood pressure).
• Any symptoms contraindicating exercise testing (e.g. chest pains).
• Any balance or dizziness problems.
• Any chronic medical conditions (whether medicated or not).
• Any bone joint problems.
• Any Physician diagnosed contraindications to exercise.
• Any other health problems that may be a cause for concern or contraindication to exercise.
• Any recent Covid vaccination (within last 2 weeks).