Lee, S., Abel, M. G., Symons, T. B., Thomas, D. T., & Yates, J. W. (2013). The relationship between acute inorganic dietary nitrate supplementation and muscle fatigue in knee extensor exercise. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 2422.

This study investigated effects of acute beetroot-juice supplementation (8.0 mMol per day of inorganic dietary nitrate) on the rate of resistance exercise fatigue (as measured by changes in peak torque) in recreationally active Ss (N = 35). Ss consumed beetroot juice or a placebo (isocaloric/isonitrogenous black currant beverage) 12 and 2.5 hours before the fatiguing exercise procedure. Peak torque was measured on the BIODEX dynamometer by performing 50 maximal concentric knee extensions at 90°/second. The change in peak torque over time was used as the fatigue index. Peak torque was averaged over five consecutive contractions and then expressed as a percentage. Blood pressure was recorded before and after exercise.

There was no significant difference between treatments in the rate of fatigue over 50 contractions. No significant differences between treatments for resting blood pressures (systolic or diastolic) were observed before the fatiguing exercise. After the fatiguing exercise, diastolic blood pressure and mean arterial pressure were both increased significantly more with beetroot-juice supplementation than in the placebo condition.

Implication. Acute bouts of beetroot-juice supplementation had no significant effect on knee-extensor muscle fatigue measured during isokinetic contractions.

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