title: Linearity and reliability of the EMG amplitude versus dynamic torque relationships for the superficial quadriceps femoris muscles.
abstract: OBJECTIVE
  The purpose of the present investigation was to determine the linearity and reliability of the electromyographic (EMG) amplitude versus dynamic torque relationships for the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM).
  
  
  METHODS
  Nine healthy men (mean +/- SD age = 25.3 +/- 4.7 years) and eleven healthy women (mean +/- SD age = 22.0 +/- 1.3 years) performed a series of randomly ordered, submaximal to maximal, concentric isokinetic muscle actions of the leg extensors at 30 degrees x s(1) on two occasions separated by at least 48 hours. During each muscle action, surface EMG signals were detected from the VL, RF and VM of the dominant thigh with bipolar surface electrode arrangements.
  
  
  RESULTS
  The coefficients of determination for the EMG amplitude versus dynamic torque relationships ranged from r2 = 0.75-0.98 and 0.64-0.99 for the VL, r2 = 0.79-0.99 and 0.60-0.98 for the RFE and r2 = 0.44-0.98 and 0.51-0.98 for the VM for trials 1 and2, respectively. In some cases, the linear EMG amplitude versus torque slope coefficient for trial 1 was significantly different from that for trial 2 for the VL and RF, but not for the VM. The intraclass correlation coefficients for the linear EMG amplitude versus torque coefficients were 0.730 (VL), 0.709 (RF), and 0.888 (VM).
  
  
  CONCLUSIONS
  These results indicated that the EMG amplitude versus dynamic torque relationships for the superficial quadriceps femoris muscles did not demonstrate enough linearity and reliability to be used for examining the contributions of neural versus hypertrophic factors to training-induced strength gains.
authors.affiliation: Department of Health and Exercise Science, University of Oklahoma, Norman, OK 73019, USA. mattstock@ou.edu
authors.forename: M S
authors.initials: MS
authors.lastname: Stock
authors.forename: T W
authors.initials: TW
authors.lastname: Beck
authors.forename: J M
authors.initials: JM
authors.lastname: DeFreitas
authors.forename: M A
authors.initials: MA
authors.lastname: Dillon
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D007551:Isotonic Contraction / Q000502:physiology*; D016014:Linear Models; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D053581:Muscle Strength Dynamometer; D005082:Physical Exertion / Q000502:physiology; D052097:Quadriceps Muscle / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results; D055815:Young Adult