Published: 26 April 2023| Version 1 | DOI: 10.17632/z8f6bj7brk.1
Vasilios Kalapotharakos




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Ten elite professional soccer players participated in the study. Participants were evaluated for body fat (%), intermittent endurance using an interval shuttle run test (ISRT), testosterone (T) and cortisol (C) concentrations, T/C ratio in July (at the beginning of the pre-season period), September (at the beginning of the competitive period), at the end of January (at the start of the second round of the competitive period) and at the end of May (at the end of the competitive season). Blood sampling was performed at rest, after a rest day, whereas the following day body composition and the ISRT, before and at the beginning of the training, respectively were assessed.Anthropometrics Characteristics Height was measured to the nearest 0.1 cm using a stadiometer, and body mass was measured to the nearest 0.1 kg. Skinfold thickness was measured at three sites (chest, abdomen, and thigh) using a Harpenden skinfold caliper. Body fat percentage (%) was calculated according to standard equations (Jackson & Pollock, 1985; Siri, 1956). Intermittent Endurance The ISRT consists of thirty second shuttle runs interspersed with fifteen second walking recovery periods (Brink et al., 2010). In order to fulfil the requirements of ISRT participants run between two lines set twenty meters apart at a pace dictated by predetermined recorded beeps. During the walking periods, players had to walk back and forth to the line. The starting test speed was 10 km/h and this speed increased by 0.5 km/h every ninety seconds. From a speed of 13 km/h, the speed increased by 1 km/h. Participants were instructed to complete as many runs as possible. The test stopped when participants could not follow the pace (more than three meters before the twenty-meter lines at two consecutive audio signals) or voluntarily quit from the run. The total number of completed twenty-meter runs was recorded as the test score (Brink et al., 2010). Blood sampling Blood samples were received in the morning (9 am) while the players were fasted for at least 10 hours. For blood sampling (10 mL), a venipuncture was performed from an anterior cubital vein with a butterfly. Participants laid down in an inclined position. Blood was stored in BD Vacutainer blood collection tubes with additional activator for coagulation. Blood was coagulated at room temperature and then subjected to centrifugation (1500 g, 4 C°, 15 min) for separation from plasma. The resulting serum after separation by centrifugation was used for the measurements. Testosterone and cortisol concentration analysis was performed with DRG Instruments immunoassay kit, using an ELISA photometer (Elisa Reader Labtech LT-4500). All sample analyses were performed in duplicate. Coefficients of analysis variability between assessor or different assessors for testosterone and cortisol concentrations remained below 5%.


Democritus University of Thrace


Sports Medicine, Sport Training, Soccer