The Effect of Dietary Nitrate on the Contractile Properties of Human Skeletal Muscle: A Systematic Review and Meta-Analysis

Purpose: To systematically review the current literature and meta-analyze the effects of dietary nitrate (NO3−) supplementation on the contractile properties of skeletal muscle.\ud \ud 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 standardized 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).\ud \ud Results: NO3− supplementation demonstrated a small improvement in PPO (SMD = 0.25, P = 0.030) and MPO (SMD = 0.28, P = 0.034) when compared to the placebo. NO3− also resulted in an enhanced time to PPO (SMD = −0.78, P