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Nitrate Supplement Benefits Contractile Forces in Fatigued but Not Unfatigued Muscle


Medicine & Science in Sports & Exercise: October 2018 - Volume 50 - Issue 10 - p 2122–2131
doi: 10.1249/MSS.0000000000001655

Purpose Evidence suggests dietary nitrate supplementation enhances low-frequency (≤20 Hz) involuntary, but not voluntary, forces in unfatigued human muscle. We investigated the hypotheses that nitrate supplementation would also attenuate low-frequency fatigue and the loss of explosive voluntary forces in fatigued conditions.

Methods In a counterbalanced double-blinded order, 17 male participants completed two experimental trials after 7 d of dietary supplementation with either nitrate-rich (NIT) or nitrate-depleted (PLA) beetroot juice. Each trial consisted of measuring isometric knee extension forces during a series of explosive maximal voluntary contractions (MVC) and involuntary tetanic contractions (at 10, 20 50, and 100 Hz) in unfatigued conditions, followed by a fatigue protocol of 60 MVC and a repeat of the tetanic contractions immediately after the 60 MVC.

Results In unfatigued conditions, there was no effect of NIT on any of the measured dependent variables, including maximal voluntary force, explosive impulse, and tetanic peak forces or peak rate of force developments at any frequency. In contrast, the percentage decline in explosive voluntary impulse from the first to the last 6 MVC in the fatigue protocol was lower in NIT (51.1% ± 13.9%) than in PLA (57.3% ± 12.4%; P = 0.039; d = 0.51). Furthermore, low-frequency fatigue determined via the percentage decline in the 20/50-Hz ratio was attenuated in NIT for tetanic peak force (NIT: 12.3% ± 12.0% vs PLA: 17.0% ± 10.1%; P = 0.110; d = 0.46) and tetanic peak rate force development (NIT: 12.3% ± 10.4% vs PLA: 20.3% ± 9.5%; P = 0.011; d = 0.83).

Conclusions Nitrate supplementation reduced the decline in explosive voluntary forces during a fatiguing protocol and attenuated low-frequency fatigue, likely due to reduced disruption of excitation–contraction coupling. However, contrary to previous findings, nitrate supplementation had no effect on contractile performance in unfatigued conditions.

Department of Life Sciences, University or Roehampton, London, UNITED KINGDOM

Address for correspondence: Neale Anthony Tillin, Ph.D., M.Sc., B.Sc., Whitelands College, University of Roehampton, Holybourne Avenue, London, SW5 4JD, United Kingdom; E-mail:

Submitted for publication November 2017.

Accepted for publication April 2018.

© 2018 American College of Sports Medicine