The effect of dietary nitrate on the contractile properties of human skeletal muscle: a systematic review and meta-analysis

Esen, Ozcan, Dobbin, Nicholas ORCID: https://orcid.org/0000-0001-7508-1683 and Callaghan, Michael ORCID: https://orcid.org/0000-0003-3540-2838 (2023) The effect of dietary nitrate on the contractile properties of human skeletal muscle: a systematic review and meta-analysis. Journal of the American College of Nutrition, 42 (4). pp. 327-338. ISSN 0731-5724

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Abstract

Purpose: To systematically review the current literature and meta-analyse the effects of dietary nitrate (NO3-) supplementation on the contractile properties of skeletal muscle. Method: A literature search of three databases was conducted in June 2021, with 19 studies meeting the inclusion criteria. Studies were included if a placebo versus dietary NO3--only supplementation protocol was used in healthy human, assessed muscle contraction or activities that was < 3 minutes in duration and focused on the lower-body. For the meta-analysis, a pooled standardised mean difference (SMD) was determined for maximum voluntary contraction (MVC) (n = 11), cycling, running and inertial load squad peak power output (PPO) (n = 8), mean power output (MPO) (n = 6) and time to PPO (n = 4). Results: NO3- supplementation demonstrated a small improvement in PPO (SMD = 0.25, P = 0.030) and MPO (SMD = 0.28, P = 0.030) when compared to the placebo. NO3- also resulted in an enhanced time to PPO (SMD = -0.78, P < 0.001). There was no clear effect of NO3- on isometric MVC (SMD = 0.03, P = 0.758). Conclusion This review reports that NO3- supplementation may have potential to enhance PPO, MPO and time to PPO during dynamic exercise, which may transfer to brief explosive actions commonly observed in sporting activities. Due to the variability in studies, we encourage researchers to use this work to explore areas where evidence in lacking and standardise the study design and procedures.