title: Construct validity of tests that measure kick performance for young soccer players based on cluster analysis: exploring the relationship between coaches rating and actual measures.
abstract: BACKGROUND
  The main aim of this study was to verify the relationship between the classification of coaches and actual performance in field tests that measure the kicking performance in young soccer players, using the K-means clustering technique.
  
  
  METHODS
  Twenty-three U-14 players performed 8 tests to measure their kicking performance. Four experienced coaches provided a rating for each player as follows: 1: poor; 2: below average; 3: average; 4: very good; 5: excellent as related to three parameters (i.e. accuracy, power and ability to put spin on the ball).
  
  
  RESULTS
  The scores interval established from k-means cluster metric was useful to originating five groups of performance level, since ANOVA revealed significant differences between clusters generated (P<0.01). Accuracy seems to be moderately predicted by the penalty kick, free kick, kicking the ball rolling and Wall Volley Test (0.44≤r≤0.56), while the ability to put spin on the ball can be measured by the free kick and the corner kick tests (0.52≤r≤0.61). Body measurements, age and PHV did not systematically influence the performance. The Wall Volley Test seems to be a good predictor of other tests.
  
  
  CONCLUSIONS
  Five tests showed reasonable construct validity and can be used to predict the accuracy (penalty kick, free kick, kicking a rolling ball and Wall Volley Test) and ability to put spin on the ball (free kick and corner kick tests) when kicking in soccer. In contrast, the goal kick, kicking the ball when airborne and the vertical kick tests exhibited low power of discrimination and using them should be viewed with caution.
authors.affiliation: Biomechanics and Motor Control Laboratory (LaBioCoM), School of Physical Education and Sport of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.|Post-Graduate Program in Rehabilitation and Functional Performance, Faculty of Medicine at Ribeirão Preto, University of São Paulo (FMRP), Ribeirão Preto, São Paulo, Brazil.
authors.forename: Luiz H
authors.initials: LH
authors.lastname: Palucci Vieira
authors.affiliation: Post-Graduate Program in Rehabilitation and Functional Performance, Faculty of Medicine at Ribeirão Preto, University of São Paulo (FMRP), Ribeirão Preto, São Paulo, Brazil.
authors.forename: Vitor L
authors.initials: VL
authors.lastname: de Andrade
authors.affiliation: Post-Graduate Program in Rehabilitation and Functional Performance, Faculty of Medicine at Ribeirão Preto, University of São Paulo (FMRP), Ribeirão Preto, São Paulo, Brazil.|CIFI2D, Faculty of Sport, University of Porto, Porto, Portugal.|Botafogo Futebol Clube, Youth Training Department, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Rodrigo L
authors.initials: RL
authors.lastname: Aquino
authors.affiliation: Biomechanics and Motor Control Laboratory (LaBioCoM), School of Physical Education and Sport of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.|Post-Graduate Program in Rehabilitation and Functional Performance, Faculty of Medicine at Ribeirão Preto, University of São Paulo (FMRP), Ribeirão Preto, São Paulo, Brazil.
authors.forename: Renato
authors.initials: R
authors.lastname: Moraes
authors.affiliation: Laboratory of Information, Vision and Action, Physical Education Department, São Paulo State University &quot;Júlio de Mesquita Filho&quot;, Bauru, São Paulo, Brazil.
authors.forename: Fabio A
authors.initials: FA
authors.lastname: Barbieri
authors.affiliation: Laboratory of Instrumentation for Biomechanics (LIB), Faculty of Physical Education (FEF), State University of Campinas, Campinas, São Paulo, Brazil.
authors.forename: Sérgio A
authors.initials: SA
authors.lastname: Cunha
authors.affiliation: Post-Graduate Program in Rehabilitation and Functional Performance, Faculty of Medicine at Ribeirão Preto, University of São Paulo (FMRP), Ribeirão Preto, São Paulo, Brazil.
authors.forename: Bruno L
authors.initials: BL
authors.lastname: Bedo
authors.affiliation: Biomechanics and Motor Control Laboratory (LaBioCoM), School of Physical Education and Sport of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil - paulosantiago@usp.br.|Post-Graduate Program in Rehabilitation and Functional Performance, Faculty of Medicine at Ribeirão Preto, University of São Paulo (FMRP), Ribeirão Preto, São Paulo, Brazil.
authors.forename: Paulo R
authors.initials: PR
authors.lastname: Santiago
mesh_terms: D000293:Adolescent; D054874:Athletic Performance / Q000502:physiology*; D001696:Biomechanical Phenomena; D005080:Exercise Test / Q000379:methods*; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D012916:Soccer / Q000502:physiology*