Five-Day Supplementation with an Isotonic Beetroot Juice Drink Improves Sprint Interval Exercise and Muscle Oxygenation in Physically Active Individuals: A Randomized Crossover Trial

This study investigated whether the addition of nitrate (from beetroot) to an isotonic drink provided over 5 days would affect sprint interval exercise (SIE) performance and muscle oxygenation. Twenty (seven female) physically active participants (mean ± SD; age 28 ± 6 years, BMI 22.6 ± 2.0 kg/m2) completed a double-blind, randomized, crossover study where they consumed 570 mL of either isotonic drink (ISO-C) or isotonic beetroot juice drink (ISO-BR) for 5 days before performing SIE (six 10 s maximal effort, interspersed with 50 s active recovery) on a cycle ergometer. Both drinks contained equal osmolality (290 mOsm/kg) but differed in the nutrients from beetroot extract, particularly the nitrate content (ISO-C: 0 mmol, ISO-BR: 12.9 mmol). ISO-BR significantly reduced the average time to peak power (ISO-C: 2.0 ± 0.18 s vs. ISO-BR: 1.6 ± 0.37 s; main effect of drink, p = 0.003, partial η2 = 0.04) and increased muscle deoxygenation (ΔHHb) (main effect of drink, p = 0.002, partial η2 = 0.021) compared to ISO-C. Five-day supplementation with ISO-BR improved the time to peak power but not the peak or mean power output for SIE compared with ISO-C.