Influence of nitrate supplementation on motor unit activity during recovery following a sustained ischemic contraction in recreationally active young males

Purpose
Dietary nitrate (NO3−) supplementation enhances muscle blood flow and metabolic efficiency in hypoxia, however, its efficacy on neuromuscular function and specifically, the effect on motor unit (MU) activity is less clear. We investigated whether NO3− supplementation affected MU activity following a 3 min sustained ischemic contraction and whether this is influenced by blood flow restriction (BFR) during the recovery period.

Method
In a randomized, double-blinded, cross-over design, 14 males (mean ± SD, 25 ± 6 years) completed two trials following 5 days of supplementation with NO3−-rich (NIT) or NO3−-depleted (PLA) beetroot juice to modify plasma nitrite (NO2−) concentration (482 ± 92 vs. 198 ± 48 nmol·L−1, p < 0.001). Intramuscular electromyography was used to assess MU potential (MUP) size (duration and area) and mean firing rates (MUFR) during a 3 min submaximal (25% MVC) isometric contraction with BFR. These variables were also assessed during a 90 s recovery period with the first half completed with, and the second half completed without, BFR.

Results
The change in MUP area and MUFR, did not differ between conditions (all p > 0.05), but NIT elicited a reduction in MUP recovery time during brief isometric contractions (p < 0.001), and during recoveries with (p = 0.002) and without (p = 0.012) BFR.

Conclusion
These novel observations improve understanding of the effects of NO3− on the recovery of neuromuscular function post-exercise and might have implications for recovery of muscle contractile function.

Trial registration
The study was registered on clinicaltrials.gov with ID of NCT05993715 on August 08, 2023.