title: Diurnal variations in physical performances related to football in young soccer players.
abstract: OBJECTIVE
  This study investigated the effects of time-of-day on aerobic and anaerobic performances during the Yo-Yo, repeated sprint ability (RSA) and the Wingate tests in young soccer players.
  
  
  METHODS
  In a counterbalanced and a random order, twenty junior male soccer players completed the Yo-Yo, the RSA, and the Wingate tests at two different times-of-day: 07:00 and 17:00 h. During the Yo-Yo test, the total distance (TD) covered and the estimated maximal aerobic velocity (MAV) were determined. The peak power (PP) during each sprint, the percentage of decrement of PP (PD) and total work (Wtotal) during the RSA test were, also, measured. In addition, during the Wingate test, the peak (P(peak)) and mean (P(mean)) powers were recorded.
  
  
  RESULTS
  During the Wingate test, P(peak) and P(mean) were significantly higher at 17:00 than 07:00 h (P<0.05) with diurnal gains of 3.1±3.6 and 2.9±3.5% respectively. During the RSA test, PP during the first two sprints, Pdec and Wtotal were, also, higher in the evening (P<0.05) with amplitudes of 4.8±4.6, 3.1±3.0, 13.1±32.1, and 4.1±2.5% respectively. Likewise, TD and MAV during the Yo-Yo test were higher at 17:00 than 07:00 h with diurnal gains of 13.1±10.7 and 4.2±3.3 respectively.
  
  
  CONCLUSIONS
  The present study confirms the daily variations of both aerobic and anaerobic performances during the Yo-Yo, the RSA, and the Wingate tests in trained young Tunisian soccer players.
authors.affiliation: Research Laboratory "Sports performance Optimization" National Center of Medicine and Science in Sports (CNMSS), Tunis, Tunisia ; Research Unit, High Institute of Sport and Physical Education, Sfax University, Tunisia.
authors.forename: Hamdi
authors.initials: H
authors.lastname: Chtourou
authors.forename: Omar
authors.initials: O
authors.lastname: Hammouda
authors.forename: Hichem
authors.initials: H
authors.lastname: Souissi
authors.forename: Karim
authors.initials: K
authors.lastname: Chamari
authors.forename: Anis
authors.initials: A
authors.lastname: Chaouachi
authors.forename: Nizar
authors.initials: N
authors.lastname: Souissi