title: Quantification of functional knee flexor to extensor moment ratio using isokinetics and electromyography.
abstract: BACKGROUND
  Evaluating moment balance around the knee helps athletic trainers set appropriate targets for injury prevention and rehabilitation programs.
  
  
  OBJECTIVE
  To examine the knee flexor (KF) to knee extensor (KE) moment ratios using the moments when each muscle group acts as an agonist and using the moments when the KE acts as an agonist and the KF acts as an antagonist.
  
  
  METHODS
  Cross-sectional.
  
  
  METHODS
  University research laboratory.
  
  
  METHODS
  Seventeen pubertal males (age = 13.7 +/- 0.2 years, height = 1.61 +/- 0.04 m, mass = 51.3 +/- 2.7 kg).
  
  
  METHODS
  The subjects performed maximal isokinetic concentric KE (KE(CON)) and eccentric KF (KF(ECC)) efforts and performed eccentric KE (KE(ECC)) and concentric KF efforts at 60 degrees /s and 180 degrees /s while we recorded the bipolar surface electromyographic (EMG) signal of the involved muscles. The KF antagonist moment was estimated from EMG-moment relationships determined during calibration KF efforts. Maximal moments were used to estimate the KF:KE ratios, and EMG-based moments were used to estimate the antagonist to agonist ratios.
  
  
  METHODS
  We calculated KF:KE ratios for various angular positions, velocities, and movement directions.
  
  
  RESULTS
  The KF(ECC):KE(CON) ratio significantly increased as the knee extended (P < .05) at increased angular velocity (P < .05), reaching a value of 3.14 +/- 1.95 at full extension. The estimated knee flexor antagonist to knee extensor agonist ratio also increased near full extension (0.32 +/- 0.21).
  
  
  CONCLUSIONS
  Although the KFs have a higher capacity to produce maximal moment near knee extension and at increased angular velocities, knee joint movement is achieved through a balanced coactivation of the 2 antagonistic muscle groups to maintain joint stability and movement efficiency. The combined use of moment and EMG data can provide additional useful information regarding muscle balance around the knee.
authors.affiliation: Aristotle University of Thessaloniki, Serres, Greece. ekellis@phed-sr.auth.gr
authors.forename: Eleftherios
authors.initials: E
authors.lastname: Kellis
authors.forename: Athanasios
authors.initials: A
authors.lastname: Katis
mesh_terms: D000293:Adolescent; D000704:Analysis of Variance; D003430:Cross-Sectional Studies; D004576:Electromyography; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology