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Team Performance, Players’ Lifestyle Habits, and Circadian Phenotype in Professional Japanese Soccer Players (J League) Hiroyuki Mizuno and Tetsuo Harada [Received January 20, 2020; Accepted May 8, 2020] Management of sleep and diurnal rhythm is important for professional athletes to maintain a competitive condition, especially for soccer players, who have a mixed schedule of morning practice and afternoon or evening games. This study aimed to identify differences in circadian phenotypes, sleep hygiene, and diurnal rhythms in soccer players according to stage (J1 or J2) and performance in the top Japanese league, the J League. We administered a questionnaire survey to 89 J League (J1 and J2) players younger than 26 years old (22.4 ± 2.1) utilizing scale of index on diurnal rhythm disturbance, which covers sleeping habits, breakfast time, and diet. Players were divided into four groups according to their ranking as of the July 2016 season—Group 1: 11 players from teams that ranked in the upper half of the J1 league; Group 2: 17 players from teams in the lower half of the J1 league; Group 3: 48 players from teams in the upper half of the J2 league; Group 4: 13 players from teams in the lower half of the J2 league. In a multiple comparison analysis, levels of sleep quality in Group 1 were higher than those in Group 2. Group 3 players showed significantly lower levels of disturbance of diurnal rhythm relative to those in Group 2. Well-regulated lifestyle habits that result in good quality sleep and less disruption in diurnal rhythms may increase competitiveness in professional soccer players. Keywords: professional soccer players, sleep quality, circadian phenotype, team performance, risk of diurnal rhythm disturbance |