2.1. Subjects
cardiovascular disease
HIGH BLOOD PRESSURE, CARDIOVASCULAR DISEASE
Sample size was calculated using online software developed by Schoenfeld [Thus, 15 football players aged between 19 and 31 were included in this study. Subjects participated in the study voluntarily and could withdraw from the study at any point. All football players were members of the same club that played in the First Division of Slovenian football. This sample was chosen as we expected it to be quite homogeneous, as the footballers had similar height and weight, level of physical fitness, and training regimen, and they were consuming two similar meals daily at the football club. The exclusion criteria were the following: all football players with a history of cardiovascular disease and high blood pressure and/or using medications that could affect the outcome of the study, injured athletes, and athletes with a history of nitrate usage less than 6 months prior to the start of the study. The testing protocol was explained to the participants and they familiarized themselves with the testing equipment prior to the first Cooper test. Two hours before the start of the first Cooper trial, the participants consumed 70 mL of concentrated beetroot juice (nitrate content: 400 mg; manufacturer: Beet It, Nitrate 400 Sport Shot, James White Drinks, Ipswich, UK) in a single dose. Alternatively, the participants consumed an equivalent amount of placebo that looked and tasted similar to the aforementioned supplement, but with nitrates removed (nitrate content ≈ 0 mg; manufacturer: Beet It, Placebo Shots, James White Drinks, Ipswich, UK). The participants then underwent bioimpedance body composition measurements (BIA 101 BIVA