Effect Of Nitrate Supplementation On Motor Unit Functions In Healthy Active Adults: 850 : Medicine & Science in Sports & Exercise

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EP-07 Metabolism and Nutrition

Effect Of Nitrate Supplementation On Motor Unit Functions In Healthy Active Adults

850

Esen, Ozcan; Callaghan, Michael; McPhee, Jamie

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Medicine & Science in Sports & Exercise 53(8S):p 283, August 2021. | DOI: 10.1249/01.mss.0000762392.61238.78
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Nitrate (NO3-) supplementation may enhance fatigue resistance and recovery, possibly because its additive effect on muscle blood flow (BF) during muscle contraction. During submaximal contractions, there are numerous ways in which the decrease in performance can be compensated for, such as motor unit (MU) recruitment, or increasing firing rate (MUFR). Given that changes in BF correlates with changes MUFR, the increased BF via NO3- supplementation may enhance MUFR during fatigue and recovery.

PROPOSE: to investigate the effect of NO3- supplementation on MU Functions during a sustained isometric contraction where BF was occluded in healthy active adults.

METHODS: In a counterbalanced double-blinded manner, 14 young adults completed two 5-day supplement period with either NO3--rich (NIT) or NO3--depleted (PLA) beetroot juice. Each trial consisted of measuring isometric knee-extension forces, and MUFR and jiggle were measured with an intramuscular concentric needle. After initial 20 sec muscle contraction at 25% maximal voluntary contraction (MVC) in unfatigued state (UF), leg blood flow was occluded for 5 min and then participants held a 25% MVC for 3 min with recording of iEMG throughout, and final 20 sec of that was taken as fatigue value (F). Participants then rested, but with the still occluded, and performed 20 sec contraction at 25% MVC at 45 sec post-fatigue (R1). Occlusion was then released, and 20 sec contraction at 25% MVC were performed after a further 45 sec (R2). Data were analysed using two-way repeated measures ANOVA.

RESULTS: The plasma NO2- concentration was increased after NO3- (475 ± 93 nmol·L-1) compared to PLA (198 ± 46 nmol·L-1, p < 0.01). MUFR decreased with fatigue and remained low in the recovery periods (UF: 9 ± 0.3 Hz; F: 7.3 ± 0.3 Hz; R1: 8 ± 0.2 Hz; R2: 7.7 ± 0.2 Hz, p < 0.01). jiggle increased as fatigue develops, remained high after recovery with occlusion, and decreased after recovery without occlusion (UF: 19.7 ± 0.8 %; F: 23.7 ± 1.4 %; R1: 27.7 ± 2.5 %; R2: 23.3 ± 1.5 %, p < 0.05). NO3- supplementation had no effect on MUFR and jiggle compared with placebo at any condition (p > 0.05).

CONCLUSION: NO3- supplementation had no ergogenic aid during muscle fatigue development or short-period recovery in healthy active adults, at least for sustained low intensity isometric contractions.

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