title: Exploratory factor analysis for differentiating sensory and mechanical variables related to muscle-tendon unit elongation.
abstract: BACKGROUND
  Stretching exercises are able to promote adaptations in the muscle-tendon unit (MTU), which can be tested through physiological and biomechanical variables. Identifying the key variables in MTU adaptations is crucial to improvements in training.
  
  
  OBJECTIVE
  To perform an exploratory factor analysis (EFA) involving the variables often used to evaluate the response of the MTU to stretching exercises.
  
  
  METHODS
  Maximum joint range of motion (ROMMAX), ROM at first sensation of stretching (FSTROM), peak torque (torqueMAX), passive stiffness, normalized stiffness, passive energy, and normalized energy were investigated in 36 participants during passive knee extension on an isokinetic dynamometer. Stiffness and energy values were normalized by the muscle cross-sectional area and their passive mode assured by monitoring the EMG activity.
  
  
  RESULTS
  EFA revealed two major factors that explained 89.68% of the total variance: 53.13% was explained by the variables torqueMAX, passive stiffness, normalized stiffness, passive energy, and normalized energy, whereas the remaining 36.55% was explained by the variables ROMMAX and FSTROM.
  
  
  CONCLUSIONS
  This result supports the literature wherein two main hypotheses (mechanical and sensory theories) have been suggested to describe the adaptations of the MTU to stretching exercises. Contrary to some studies, in the present investigation torqueMAX was significantly correlated with the variables of the mechanical theory rather than those of the sensory theory. Therefore, a new approach was proposed to explain the behavior of the torqueMAX during stretching exercises.
authors.affiliation: Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil.
authors.forename: Mauro H
authors.initials: MH
authors.lastname: Chagas
authors.affiliation: Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil.
authors.forename: Fabrício A
authors.initials: FA
authors.lastname: Magalhães
authors.affiliation: Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil.
authors.forename: Gustavo H C
authors.initials: GH
authors.lastname: Peixoto
authors.affiliation: Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil.
authors.forename: Beatriz M
authors.initials: BM
authors.lastname: Pereira
authors.affiliation: Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil.
authors.forename: André G P
authors.initials: AG
authors.lastname: Andrade
authors.affiliation: Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil.
authors.forename: Hans-Joachim K
authors.initials: HJ
authors.lastname: Menzel
mesh_terms: D004576:Electromyography; D005163:Factor Analysis, Statistical; D006801:Humans; D009119:Muscle Contraction / Q000502:physiology*; D052580:Muscle Stretching Exercises / Q000592:standards; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D013710:Tendons / Q000502:physiology*; D019415:Torque