2. Materials and Methods
This was a randomized, placebo-controlled, double-blind, crossover trial consisting of two phases: introductory testing and the first performance assessment (Cooper test) and the second performance assessment. Subjects were randomly assigned into one of two groups (A and B) using simple randomization with Excel by an outside party within the research institution; the details of the randomization series were unknown to any of the investigators or the coordinator. The details of the randomization were kept in a secure place (personal laptop secured with a personal code) by the researcher. Based on the randomization, the researcher labeled the provided supplements and placebo drinks accordingly to be used in the intervention trial. After all relevant data were gathered and the trials were finished, we gained access to data as to which football players received nitrate supplementation in the first trial and placebo in the second trial prior to the performance assessment, and which football players received placebo supplementation in the first trial and nitrate supplementation in the second trial prior to the performance assessment. Details around the performance assessment and supplementation strategies are explained in 