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Effects of Citrulline Malate and Beetroot Juice Supplementation on Blood Flow, Energy Metabolism, and Performance During Maximum Effort Leg Extension Exercise

Trexler, Eric T.1,2; Keith, Dale S.2; Schwartz, Todd A.3; Ryan, Eric D.1,2; Stoner, Lee1,2; Persky, Adam M.4; Smith-Ryan, Abbie E.1,2

The Journal of Strength & Conditioning Research: September 2019 - Volume 33 - Issue 9 - p 2321–2329
doi: 10.1519/JSC.0000000000003286
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Trexler, ET, Keith, DS, Schwartz, TA, Ryan, ED, Stoner, L, Persky, AM, and Smith-Ryan, AE. Effects of citrulline malate and beetroot juice supplementation on blood flow, energy metabolism, and performance during maximum effort leg extension exercise. J Strength Cond Res 33(9): 2321–2329, 2019—Citrulline malate (CitMal) and beetroot juice (BEET) are increasingly popular ergogenic aids, but few studies have rigorously investigated their effects on resistance exercise performance and underlying mechanisms. The current randomized, double-blind, crossover study evaluated the effects of CitMal and BEET supplementation on blood flow, metabolic efficiency, and performance during maximal isokinetic leg extension exercise. After familiarization, 27 recreationally active men (age: 22 ± 4 years) completed 3 visits in which subjects ingested a treatment beverage (CitMal [8 g], BEET [400-mg nitrate], or placebo [PLA]), followed by a 2-hour rest period, warm-up, and 5 sets of 30 concentric leg extensions. Before and after exercise, ultrasound was used to measure diameter (aDIAM) and blood flow (aBF) of the superficial femoral artery, along with cross-sectional area and echo intensity of the vastus lateralis. Plasma analytes (lactate, nitrate/nitrite [NOx], and urea nitrogen [BUN]) were also assessed at these times, and indirect calorimetry was used to measure energy expenditure and respiratory exchange ratio before and during exercise. Resting NOx values were higher in BEET (233.2 ± 1.1 μmol·L−1) compared with CitMal (15.3 ± 1.1, p < 0.0001) and PLA (13.4 ± 1.1, p < 0.0001). Postexercise NOx values, adjusted for resting differences, were higher in BEET (86.3 ± 1.2 μmol·L−1) than CitMal (21.3 ± 1.1, p < 0.0001) and PLA (18.1 ± 1.1, p < 0.0001). No other variables were affected by treatment (all p > 0.05). While BEET increased NOx, neither treatment was found to enhance performance, blood flow, metabolic efficiency, nor the hormonal response to leg extension exercise.

1Department of Allied Health Sciences, Human Movement Science Curriculum, University of North Carolina, Chapel Hill, North Carolina;

2Department of Exercise and Sport Science, Applied Physiology Laboratory, University of North Carolina, Chapel Hill, North Carolina;

3Department of Biostatistics, Gillings School of Global Public Health, University of North Carolina, Chapel Hill, North Carolina; and

4Eshelman School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina

Address correspondence to Dr. Abbie E. Smith-Ryan, abbsmith@email.unc.edu.

Copyright © 2019 by the National Strength & Conditioning Association.