A team of researchers from the United States, Netherlands and United Kingdom set out to assess the effect of acute and short-term supplementation with nitrate-rich beetroot juice on performance outcomes and muscle oxygenation during bench press and back squat exercises.
“Compared to running and cycling, relatively few studies have investigated the impact of dietary NO3−supplementation on resistance exercise performance (e.g., muscle power output), and studies conducted to date have yielded conflicting results,” the researchers wrote.
The research builds on the interest in NO3− supplementation as a nutritional intervention for exercise performance, as it enhances the production of nitric oxide (NO), a “ubiquitous signaling molecule that regulates cardiovascular, metabolic and contractile processes.”
The double-blind crossover study randomly assigned 14 healthy recreationally active men to two test groups over two supplementation periods, separated by a minimum washout period of five days.
Over the four-day trial, the treatment group received two nitrate-rich beetroot juice shots a day (2.4 fl. oz. each), while the control group consumed a nitrate-depleted beetroot juice placebo. Both test products were provided by Beet It Sport, part of UK-based James White Drinks, Ltd. and supplier of standardized beetroot juice shots to the research community.
To determine muscular power, velocity and endurance, participants completed upper body and lower body resistance exercises on the first and last day of the trial. On test days, beverages were administered as double doses 2 ½ hours prior to exercise, compared to morning and evening treatments on the other two trial days.
“This four-day protocol was chosen to simulate a potential supplementation regimen an athlete would adopt prior to competition and to provide insight to acute compared to short-term NO3− supplementation periods,” the study noted.
Researchers assessed plasma samples, mood, muscle oxygenation, muscular power, velocity and endurance.
“The principal novel finding of the current study was that an ergogenic effect of NO3−supplementation was attained during bench press repetitions-to-failure, with no effect on this outcome variable during back squat exercise,” the study concluded.
“This observation is compatible with the notion that dietary NO3− supplementation may preferentially elicit beneficial physiological and functional effects on type II muscle fibers.”
Researchers also found acute but not multiday beetroot juice supplementation increased plasma NO3− , but plasma NO2− was elevated similarly after acute and four-day NO3− supplementation. The treatment group showed no effect on power and velocity during the back squat or bench press exercise.
The study calls for further research to elucidate the efficacy of acute versus longer-term supplementation, the influence on muscle oxygenation and the impact of fatigue development on performance assessments during resistance exercise.
The researchers said no external funding was used to conduct the study.
Source: Nutrients 2022, 14, 3703
“Effects of Dietary Nitrate Supplementation on Performance and Muscle Oxygenation during Resistance Exercise in Men”
Authors: Rachel Tan et al.