title: Change of direction ability in young elite soccer players: determining factors vary with angle variation.
abstract: BACKGROUND
  The ability to change direction is considered of paramount importance in team sports. Currently there is a lack of consensus regarding the most important physical factors that determine change of direction (COD) ability. Therefore, the aim of this study was to examine the relationship between COD ability and targeted selected physical attributes of sprinting, isometric strength and explosive power.
  
  
  METHODS
  Thirty-one young elite soccer players (mean±SD, age =17.4±0.6 years, height =177±0.5 cm; leg length =96.9±3.3 cm, body-mass =69.0±6.2 kg) were recruited. A total of eight COD tasks consisting of; a 5-m sprint then a COD of 45°, 90°, 135° or 180° followed by another 5m sprint were performed using dominant (DL) and non-dominant legs (NDL). Physical tests including a 10-m Straight-Line Sprint Test, 12 lower limb isometric strength tests, and jumping tests including: 1) five alternate Leg Jump Test; 2) triple hop distance (DL and NDL); and 3) Standing Broad Jump Test were performed.
  
  
  RESULTS
  Stepwise multiple regression analysis showed that the physical attributes explained between 30% and 74% of the variance of the COD performance. Furthermore, these physical attributes were dependent upon COD angle and direction.
  
  
  CONCLUSIONS
  The affecting variables of the COD performance differ according to the angle of COD and the leg used to turn. Moreover, isometric strength of the lower-limb muscles represented a major determinant factor of the COD-ability. Consequently, physical fitness coaches should include isometric muscle strengthening exercises in addition to traditional dynamic muscle strength exercises. Moreover, they should implement specific lower limb strength exercises depending on players' deficit in each COD's angles.
authors.affiliation: Tunisian Research Laboratory &quot;Sport Performance Optimization&quot;, National Center of Medicine and Science in Sports, Tunis, Tunisia - mehdirwissi@gmail.com.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Rouissi
authors.affiliation: Tunisian Research Laboratory &quot;Sport Performance Optimization&quot;, National Center of Medicine and Science in Sports, Tunis, Tunisia.
authors.forename: Moktar
authors.initials: M
authors.lastname: Chtara
authors.affiliation: Servette Football Club, Geneva, Switzerland.
authors.forename: Adam
authors.initials: A
authors.lastname: Owen
authors.affiliation: Athlete Health and Performance Aspetar, Qatar Orthopedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Angus
authors.initials: A
authors.lastname: Burnett
authors.affiliation: Athlete Health and Performance Aspetar, Qatar Orthopedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Karim
authors.initials: K
authors.lastname: Chamari
mesh_terms: D000293:Adolescent; D054874:Athletic Performance / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D035002:Lower Extremity / Q000502:physiology; D008297:Male; D053580:Muscle Strength / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology; D012420:Running / Q000502:physiology*; D012916:Soccer / Q000502:physiology*