High intensity interval training in soccer players: the chronotype effect

INTERVENTION: The single session of high‐intensity endurance interval training protocol will consist of 4 bouts of 4 minutes (4X4) at 90‐95% HRmax with 3 min of active recovery at 50‐60% HRmax. The training intervention will start with a standardized 10‐min warm‐up and will end with a 3‐min cool‐down period at a self‐selected intensity. The acute training sessions will be conducted outdoor by an exercise physiologist, on an athletic track in dry, windless weather conditions with a temperature about 15‐20 degrees. Subjects will be trained in groups. After a baseline assessment subjects will be randomly assigned morning training that started performing the high intensity interval training protocol at 8.00 am or evening training that started performing the high intensity interval training protocol at 8.00 pm. Both groups will be blinded about the aim of the study. Adherence will be monitored registering the attendance of players during each training session CONDITION: Autonomic Control Mood States Sleep Quality PRIMARY OUTCOME: Autonomic control, assessed by heart rate variability (via beat‐to‐beat heart rate monitor). Salivary Cortisol Concentration Sleep quality, assessed using actigraphy (worn for one full night's sleep at each timepoint). SECONDARY OUTCOME: The profile of mood states will be assessed using a 32 items questionnaire which reflects an individual’s mood on five primary dimensions (depression, fatigue, vigour, tension and anger). Subjects will complete the POMS data will be analysed for each specific dimension and an “energy index” will be calculated as “vigour‐fatigue” and used to monitor changes in energy balance. ; INCLUSION CRITERIA: More than 18 years old; male; being soccer players of at least 5‐10 years; 6 hours of training a week; with a morning or evening chronotype scores