title: Effect of the contraction of medial rotators of the tibia on the electromyographic activity of vastus medialis and vastus lateralis.
abstract: OBJECTIVE
  This study attempted to assess if the resisted contraction of medial rotators of the tibia increases the ratio between the activity of vastus medialis (VM) and vastus lateralis (VL) during maximal isometric contractions (MIC) of the quadriceps femoral (QF) muscle at 90 degrees of knee flexion.
  
  
  METHODS
  About 24 female subjects participated in this study, performing four series MIC of the QF. In the first series subjects performed only MIC of the QF muscle, whereas in the other three there was MIC of the QF with resisted contraction of medial rotators of the tibia, with the tibia positioned in medial, neutral and lateral rotation. During each contraction, VM and VL electromyographic signal (EMGs) and QF force were collected, being the EMGs root mean square (RMS) used to access the activity level of these muscles.
  
  
  RESULTS
  The use of the General Linear Model (GLM) test showed that for alpha=0.05 there was a significant increase in the VM:VL ratio when the resisted contraction of medial rotators of the tibia was performed with the tibia in medial (p=<0.0001), neutral (p=<0.0001) and lateral rotation (p=0.001). The same test showed that during MIC of the QF associated to resisted contraction of medial rotators of the tibia there were no significant differences in the VM:VL ratio between the three tibial rotation positions adopted (p=0.866 [medial-neutral]; p=0.106 [medial-lateral]; p=0.068 [neutral-lateral]).
  
  
  CONCLUSIONS
  The resisted contraction of medial rotators of the tibia increases the VM:VL ratio during MIC of the QF and the tibial rotation position does not influence the VM:VL ratio during MIC associated to resisted contraction of medial rotators of the tibia.
authors.affiliation: Department of Physiotherapy, Escola Superior de Tecnologia de Saúde do Instituto Politécnico do Porto, Rua Valente Perfeito, 322, 4400-330 Vila Nova de Gaia, Portugal. andreia.asps@gmail.com
authors.forename: Andreia
authors.initials: A
authors.lastname: Sousa
authors.forename: Rui
authors.initials: R
authors.lastname: Macedo
mesh_terms: D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D012399:Rotation; D013848:Thigh / Q000502:physiology; D013977:Tibia / Q000502:physiology*; D055815:Young Adult