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Table 1 Inclusion criteria

From: Effect of food sources of nitrate, polyphenols, L-arginine and L-citrulline on endurance exercise performance: a systematic review and meta-analysis of randomised controlled trials

Inclusion criteria Rationale
Consumption of nitric oxide precursors only via consumption of whole foods, juices, concentrates or plant extracts. Studies must explicitly state the food source(s) of these compounds. Differences in bioavailability between food and synthetic sources.
Foods could not be consumed in combination with other (non-nitric oxide precursor) foods/supplements that may influence endurance exercise performance (e.g. caffeine) unless the comparator group also contains these components. Such interventions will be included in the qualitative synthesis only. Confounds the ability to infer the effect of increasing intake of nitric-oxide precursors.
Report an external (or externally derived) measure of maximal endurance exercise performance in a test of at least two minutes durations. Maximise the contribution of the aerobic energy system to exercise performance and thus provide a measure of endurance exercise performance.
Intermittent-type performance tests required a work duration of at least two minutes and could not have between-repetition recovery intervals of >60 secs Maximise the contribution of the aerobic energy system to exercise performance and thus provide a measure of endurance exercise performance.
Performance tests conducted in normobaric, normoxic and temperate conditions. Variant conditions may influence the function of the nitric oxide pathway and the effects of nitric oxide-related supplementation
Where performance tests were acutely repeated (e.g. repeated time trials), only data from the initial performance test were considered eligible. Performance in subsequent trial(s) may be confounded by initial performance and factors which influence recovery.
Study sample participants aged 18-65 years Exclude adolescent and older adult populations due to age-based differences in vascular function and oxidative stress