Effects of Acute Beetroot Juice on Aerobic Performance and Muscle Oxygenation in Amateur Female Soccer Players

Keywords

• Beetroot juice
• Dietary nitrate
• Aerobic performance
• Muscle oxygenation
• Female soccer players

Lead sponsor

Sakarya Applied Sciences University is the lead sponsor of 5 studies on the registry; 3 are open to participants now.

Study arms

• Experimental
  Beetroot Juice, Then Placebo

  Participants first received 70 mL of nitrate-rich beetroot juice containing 6.4 mmol nitrate. After a 7-day washout period, they received 70 mL of low-nitrate blackcurrant placebo containing \<0.1 mmol nitrate. Each beverage was consumed 2.5 hours before the 12-minute exercise test.

  Dietary Supplement: Nitrate-rich beetroot juice · Other: Low-nitrate blackcurrant placebo beverage

• Experimental
  Placebo,Then Beetroot Juice

  Participants first received 70 mL of low-nitrate blackcurrant placebo containing \<0.1 mmol nitrate. After a 7-day washout period, they received 70 mL of nitrate-rich beetroot juice containing 6.4 mmol nitrate. Each beverage was consumed 2.5 hours before the 12-minute exercise test.

  Dietary Supplement: Nitrate-rich beetroot juice · Other: Low-nitrate blackcurrant placebo beverage

Interventions

• Dietary supplementNitrate-rich beetroot juice

  Participants consumed a single 70 mL dose of nitrate-rich beetroot juice (Beet It Pro Elite Shot, James White Drinks Ltd., Ipswich, UK) containing 6.4 mmol (approximately 400 mg) of nitrate. The supplement was ingested 2.5 hours before the 12-minute exercise test.

• OtherLow-nitrate blackcurrant placebo beverage

  Participants consumed a single 70 mL dose of low-calorie blackcurrant beverage (Pfanner, Austria) containing negligible nitrate (\<0.1 mmol). The placebo was ingested 2.5 hours before the 12-minute exercise test.

Primary outcomes

1. Distance Covered During the 12-Minute Cooper Test

   Total distance covered, expressed in meters, during a self-paced treadmill-adapted 12-minute Cooper test. Participants were instructed to cover the greatest possible distance within 12 minutes and were allowed to adjust treadmill speed throughout the test.

   Time frame: During the 12-minute exercise test performed 2.5 hours after supplementation in each crossover condition

Secondary outcomes

1. Estimated Maximal Oxygen Uptake (VO₂max)

   Estimated maximal oxygen uptake (VO₂max), expressed as mL·kg-¹·min-¹, was calculated from the total distance covered during the treadmill-adapted 12-minute Cooper test using the classical Cooper equation.

   Time frame: At completion of the 12-minute exercise test performed 2.5 hours after supplementation in each crossover condition.

2. Muscle Oxygen Saturation (SmO₂)

   Muscle oxygen saturation (SmO₂), expressed as a percentage, was assessed in the vastus lateralis using near-infrared spectroscopy (Moxy Monitor, Fortiori Design LLC, Spicer, MN, USA).

   Time frame: Baseline (2 minutes before warm-up), during the 12-minute exercise test, and early post-exercise (approximately 2-3 minutes after exercise) in each crossover condition.

3. Heart Rate

   Heart rate, expressed as beats per minute, was recorded using a Polar V800 heart rate monitor. Values were summarized as the 1-minute pre-exercise mean, mean heart rate during the 12-minute exercise test, and recovery heart rate.

   Time frame: Pre-exercise, continuously during the 12-minute exercise test, approximately 2-3 minutes post-exercise, and approximately 29-30 minutes post-exercise in each crossover condition.

4. Blood Pressure

   Blood pressure, expressed in mmHg, was measured using an automated blood pressure monitor (Omron M2, Omron Healthcare Co., Kyoto, Japan). Three consecutive readings were obtained at each time point and averaged.

   Time frame: Before supplementation, pre-exercise, 3 minutes post-exercise, and 30 minutes post-exercise in each crossover condition.

5. Blood Glucose

   Capillary blood glucose, expressed in mg/dL, was measured from a finger-prick blood sample using a portable glucose analyzer (Plusmed Accuro, Taiwan).

   Time frame: Immediately before supplementation, pre-exercise (2 minutes before warm-up), and immediately post-exercise in each crossover condition.

6. Rating of Perceived Exertion (RPE)

   Rating of perceived exertion was assessed using the Borg 6-20 scale, where higher scores indicate greater perceived exertion.

   Time frame: Baseline and immediately post-exercise in each crossover condition.

Individual participant data

Plan to share: No — The data supporting the findings of this study are available from the corresponding author upon reasonable request, subject to ethical and privacy considerations.