Int J Sports Med 2018; 39(09): 688-695
DOI: 10.1055/s-0044-100389
Training & Testing
© Georg Thieme Verlag KG Stuttgart · New York

Developmental Changes in Isometric Strength: Longitudinal Study in Adolescent Soccer Players

Authors

  • Joao P. Duarte

    1   Faculty of Sports Sciences and Physical Education, University of Coimbra, Coimbra, Portugal
    2   uid/dtp/04213/2016, University of Coimbra, Coimbra, Portugal
  • João Valente-dos-Santos

    2   uid/dtp/04213/2016, University of Coimbra, Coimbra, Portugal
    3   Faculty of Physical Education and Sport, Lusofona University of Humanities and Technologies, Lisbon, Portugal
  • Manuel J. Coelho-e-Silva

    1   Faculty of Sports Sciences and Physical Education, University of Coimbra, Coimbra, Portugal
    2   uid/dtp/04213/2016, University of Coimbra, Coimbra, Portugal
  • R. M. Malina

    3   Faculty of Physical Education and Sport, Lusofona University of Humanities and Technologies, Lisbon, Portugal
  • Dieter Deprez

    4   Department of Kinesiology and Health Education, University of Texas, Austin, Texas, USA
  • Renaat Philippaerts

    5   Club Brugge KV, Brugge, Belgium
  • Matthieu Lenoir

    6   Department of Movement and Sports Science, Ghent University, Ghent, Belgium
  • Roel Vaeyens

    5   Club Brugge KV, Brugge, Belgium
    6   Department of Movement and Sports Science, Ghent University, Ghent, Belgium
Further Information

Publication History



accepted after revision 01 January 2018

Publication Date:
20 June 2018 (online)

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Abstract

This study aimed to examine longitudinal changes in isometric strength of the knee extensors (ImKE) and knee flexors (ImKF) at 30° and 60°. The sample was composed of 67 players aged 11.0–13.9 years at baseline over five years. Stature, body mass, skinfolds, and isometric strength (ImKE30°, ImKF30°, ImKE60° and ImKF60°) were measured. Fat mass and fat-free mass (FFM) were derived from skinfolds. Skeletal age was obtained using TW2 RUS. Multilevel random effects regression analyses extracted developmental polynomial models. An annual increment on chronological age (CA) corresponded to 5.6 N (ImKE30°), 2.7 N (ImKF30°), 4.6 N (ImKE60°) and 1.5 N (ImKF60°). An increment of 1 kg in FFM predicted isometric strength as follows: 1.2 N (ImKE30°), 2.1 N (ImKF30°), 3.1 N (ImKE60°) and 2.0 N (ImKF60°). The following equations were obtained: ImKE30°=5.759×CA+1.163×FFM; ImKF30°=−19.369+2.691×CA+0.693×CA2+2.108×FFM; ImKE60°=4.553×CA+3.134×FFM; and, ImKF60°=-19.669+1.544×CA+2.033×FFM. Although skeletal maturity had a negligible effect on dependent variables, age and body size, based on FFM, were relevant longitudinal predictors. During adolescence, systematic assessment of knee extensors and knee flexors are strongly recommended to prevent impairment of knee muscle groups.