Effects of Acute Beetroot Juice on Aerobic Performance and Muscle Oxygenation in Amateur Female Soccer Players
This randomized, double-blind, placebo-controlled crossover study evaluated the acute effects of nitrate-rich beetroot juice supplementation on aerobic performance, muscle oxygenation, and selected physiological responses in amateur female soccer players. Thirteen participants completed two experimental conditions in randomized order, separated by a 7-day washout period. In one condition, participants consumed 70 mL of nitrate-rich beetroot juice containing 6.4 mmol of nitrate, while in the other condition they consumed an equal volume of low-nitrate blackcurrant placebo containing \<0.1 mmol of nitrate. Each beverage was consumed 2.5 hours before exercise testing. Aerobic performance was assessed using a treadmill-adapted 12-minute Cooper test. Total distance covered and estimated maximal oxygen uptake (VO₂max) were evaluated as performance outcomes. Muscle oxygen saturation was monitored using near-infrared spectroscopy. Heart rate, blood pressure, blood glucose, and rating of perceived exertion were also assessed at predefined time points. Participants and investigators conducting the experimental procedures were blinded to the supplementation condition, and the supplementation sequence was generated by an independent researcher who was not involved in the experimental procedures or statistical analyses.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
OTHER
Masking
DOUBLE
Enrollment
13
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.
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.
Sakarya University of Applied Sciences Esentepe Campus Sports Sciences Faculty
Sakarya, Turkey (Türkiye)
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
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.
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.
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.
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.
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Time frame: Before supplementation, pre-exercise, 3 minutes post-exercise, and 30 minutes post-exercise in each crossover condition.
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.
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.