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DIETARY NITRATE SUPPLEMENTATION ENHANCES HEAVY LOAD CARRIAGE PERFORMANCE IN MILITARY CADETS

Abstract

Nicholas Cole Bordonie1, Michael J. Saunders, FACSM2, Joaquin Ortiz de Zevallos3, Stephanie P. Kurti2, Nicholas D. Luden2, Jenny H. Crance4, Daniel A. Baur4. 1Auburn University, Auburn, AL. 2James Madison University, Harrisonburg, VA. 3University of Virginia, Charlottsville, VA. 4Virginia Military Institute, Lexington, VA.

BACKGROUND: Soldiers are commonly required to carry heavy loads (> 35 kg) that increase metabolic rates and exercise intensity, which can negatively impact performance. The purpose of this study was to determine the effects of dietary nitrate (NO3−) supplementation on physiological responses, cognitive function, and performance during heavy load carriage in military cadets. METHODS: Ten healthy males (81.0 ± 6.5 kg; 180.0 ± 4.5 cm; 56.2 ± 3.7 ml·kg·min-1 VO2max) consumed 140 mL·d-1 of beetroot juice (BRJ; 12.8 mmol NO3−) or placebo (PL) for six days preceding an exercise trial consisting of 45 min of load carriage (55% body mass) at 4.83 km·h-1 and 1.5% grade, followed by a 1.6-km time-trial (TT) at 4% grade. Gas exchange, heart rate, and perceptual responses were assessed at during constant-load exercise and the TT. Cognitive function was assessed immediately prior to, during, and post-exercise via the psychomotor vigilance test. RESULTS: There were no effects of BRJ on constant-load gas exchange or perceptual responses, and cognitive function was unchanged at all time points. However, there were small effect sizes (Cohen’s d) for response times and lapses, respectively, during-exercise (PL vs. BRJ: +15.2 ms and +2.3; d = 0.26 and 0.28) and in the change from rest to exercise (PL vs. BRJ: +18.2 ms and +3.2; d = 0.49 and 0.48). Additionally, post-TT HR (188 ± 7.1 vs. 185 ± 7.4; d = 0.40; p =0.03), mean tidal volume (2.15 ± 0.27 vs. 2.04 ± 0.23; p = 0.02; d = 0.47), and performance over 1.6 km (770.9 ± 78.2 s vs. 809.8 ± 61.4 s; p = 0.03; d = 0.63) were increased/enhanced during the TT with BRJ versus PL. CONCLUSIONS: BRJ supplementation improves heavy load carriage performance in military cadets possibly as a result of attenuated respiratory muscle fatigue, rather than enhanced exercise economy.

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