Exclusion criteria | Rationale |
---|---|
Performance assessed during recreational, open entry events (e.g. marathon) | Lack of controlled conditions |
Performance only measured as an indicator of recovery (e.g. hours or days following an exercise stimulus designed to induce damage/stress) rather than being assessed at maximum performance capacity or more closely following a standardised preload | To reduce the influence of post-exercise recovery, which reflects a different mechanism |
Treatment comparator was a food rich in nitric oxide precursors (unless differences in content are quantified) | Difficult to infer how much treatment increases nitric oxide precursors relative to control |
Supplement contained >1mg caffeine per kg of body mass, as calculated from participant mean mass | Avoid ergogenic effects seen with higher intakes of caffeine [32] |
Performance test intensity was acutely regulated by heart rate or oxygen consumption. | Nitric oxide supplements may alter these internal measures and thereby confound the ability to identify effects on endurance exercise performance. |