Table 4.
Summary of studies investigating the effect of synergistic effects of multiple nitric oxide precursors.
| Study | Subjects | Design | Intervention | Performance Tests | Main Findings |
|---|---|---|---|---|---|
| L-citrulline/L-arginine + nitrates | |||||
| Burgos et al. (2022) [120] | 32 male endurance athletes (32.2 ± 4.9 y; 22.6 ± 1.8 kg·m2) | Randomized, double-blind, placebo-controlled trial | 3 g L-citrulline vs. 300 mg nitrates vs. 3 g L-citrulline + 300 mg nitrates vs. placebo; 9 weeks | Horizontal jump test Handgrip dynamometer test 1 min abdominal test |
↔ horizontal jump distance * ↔ handgrip strength ↔ abdominal crunch repetitions * |
| Le Roux-Mallouf et al. (2017) [116] | 14 healthy, physically active men and women (27.8 ± 7.5 y; 64.3 ± 9.1 kg) | Randomized, double-blind, placebo-controlled, crossover study | BRJ containing 1200 mg nitrates + 6 g L-citrulline vs. placebo; 90 min prior | Thigh ischemia-reperfusion test | ↑ post-occlusive hemoglobin/oxyhemoglobin response suggesting enhanced vasodilation |
| Le Roux-Mallouf, Laurent, et al. (2019) [117] | 15 healthy, physically active men (28 ± 6 y; 73 ± 6 kg) | Randomized, double-blind, placebo-controlled, crossover study | BRJ (520 mg nitrate) vs. BRJ (520 mg nitrate) + 6 g L-citrulline vs. BRJ (520 mg nitrate + 6 g L-arginine; 90 min prior | Thigh ischemia-reperfusion test Isometric knee extension repetitions-to-failure (5 s on-4 s off at 45% of MVC) |
↑ post-occlusive hemoglobin/oxyhemoglobin response suggesting enhanced vasodilation (nitrate and nitrate/citrulline group) ↔ knee extension repetitions |
| Le Roux-Mallouf, Pelen, et al. (2019) [118] | 24 healthy older adult men and women (64 ± 2 y; 73.5 ±6.1 kg) | Randomized, double-blind, placebo-controlled trial | 6 g L-citrulline + 520 mg nitrate vs. placebo; 4 weeks | Thigh ischemia-reperfusion test Incremental isometric knee extension test |
↔ ischemia-reperfusion test ↔ knee extension performance |
| Le Roux-Mallouf et al. (2020) [119] | 24 healthy men and women (26 ± 3 y; 76.4 ± 5.1 kg) | Randomized, double-blind, placebo-controlled trial | 6 g L-citrulline + 520 mg nitrate vs. placebo; 8 weeks | Thigh ischemia-reperfusion test Incremental isometric knee extension test |
↔ ischemia-reperfusion test ↑ maximal knee extensor strength ↔ knee extension performance * |
| L-citrulline + L-arginine | |||||
| Suzuki et al. (2019) [115] | 20 male collegiate soccer players (19.0 ± 0.2 y; 65.4 ± 0.1 kg) | Randomized, double-blind, placebo-controlled, crossover study | 1.2 g L-citrulline + 1.2 g L-arginine vs. placebo; 7 days (60 min prior) | 10 min full-power cycling test | ↑ mean power output ↔ peak pedaling speed ↑ subjective “leg muscle soreness” ↑ subjective “ease of pedaling” |
↑ = significantly greater (p < 0.05) than placebo; ↓ = significantly less (p < 0.05) than placebo; ↔ = no significant difference between supplement and placebo; * = trend towards significance (p < 0.10); BRJ = beetroot juice; MVC = maximal voluntary contraction; MIPS = multi-ingredient pre-workout supplement.