title: Peak torque and muscle balance in the knees of young U-15 and U-17 soccer athletes playing various tactical positions.
abstract: BACKGROUND
  Soccer is a sport that is practiced worldwide and has been investigated in its various aspects, particularly muscle strength, which is an essential motor skill for sports performance. The objective of this study was to investigate the peak torque and muscle balance on the knee extensor and flexor of young soccer players in the tactical positions of goalkeeper, defender, full back, midfielder, defensive midfielder and striker, as well as to determine which field position has the highest peak torque.
  
  
  METHODS
  Forty-nine male players were recruited and divided into two categories during the preparatory period of the season: the Under-15 (U-15) group (N.=23, mean age 14.7±0.5 years, body mass 58.2±10.5 kg, body height 168.5±7.6 cm), and the Under-17 (U-17) group (N.=26, mean age 16.8±0.4 years, body mass 69.2±7.9 kg, body height 176.2±6.6 cm).
  
  
  RESULTS
  The U-17 athletes presented a higher peak torque in all the movements of flexion and extension in the two angular velocities (i.e. 60°/s and 300°/s), but only the dominant knee extensor at 300°/s was significantly different between the two categories as well as the percentage change in peak torque compared between U-15 and U-17 was always above 20%. The peak torque variation in the U-17 category (i.e. mostly above 20%) highlights a higher peak torque compared to U-15 athletes.
  
  
  CONCLUSIONS
  The muscular deficit of the two categories presented a low average of 10-15%, indicating a good muscle balance between knee extensors and flexors. Finally, goalkeepers and defenders achieved the highest peak torque amongst the field positions.
authors.affiliation: Laboratory of Biomechanics, Faculty of Physical Education and Physiotherapy, University of Passo Fundo, Passo Fundo, Brazil.
authors.forename: Cleiton
authors.initials: C
authors.lastname: Chiamonti Bona
authors.affiliation: School of Physical Education and Sports, University of São Paulo, Ribeirão Preto, Brazil.
authors.forename: Hugo
authors.initials: H
authors.lastname: Tourinho Filho
authors.affiliation: Department of Health Sciences, Public University of Navarra, Tudela, Spain - mikel.izquierdo@gmail.com.
authors.forename: Mikel
authors.initials: M
authors.lastname: Izquierdo
authors.affiliation: Department of Sports Sciences, University of Beira Interior, Covilhã, Portugal.|Research Centre in Sports, Health and Human Development, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal.
authors.forename: Ricardo M
authors.initials: RM
authors.lastname: Pires Ferraz
authors.affiliation: Department of Sports Sciences, University of Beira Interior, Covilhã, Portugal.|Research Centre in Sports, Health and Human Development, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal.
authors.forename: Mário C
authors.initials: MC
authors.lastname: Marques
mesh_terms: D000293:Adolescent; D054874:Athletic Performance / Q000502:physiology; D003430:Cross-Sectional Studies; D006801:Humans; D007717:Knee / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular; D012916:Soccer / Q000502:physiology*; D019415:Torque