title: Reliability of quadriceps surface electromyography measurements is improved by two vs. single site recordings.
abstract: OBJECTIVE
  The reliability of surface electromyography (sEMG) is typically modest even with rigorous methods, and therefore further improvements in sEMG reliability are desirable. This study compared the between-session reliability (both within participant absolute reliability and between-participant relative reliability) of sEMG amplitude from single vs. average of two distinct recording sites, for individual muscle (IM) and whole quadriceps (WQ) measures during voluntary and evoked contractions.
  
  
  METHODS
  Healthy males (n = 20) performed unilateral isometric knee extension contractions: voluntary maximum and submaximum (60%), as well as evoked twitch contractions on two separate days. sEMG was recorded from two distinct sites on each superficial quadriceps muscle.
  
  
  RESULTS
  Averaging two recording sites vs. using single site measures improved reliability for IM and WQ measurements during voluntary (16-26% reduction in within-participant coefficient of variation, CVW) and evoked contractions (40-56% reduction in CVW).
  
  
  CONCLUSIONS
  For sEMG measurements from large muscles, averaging the recording of two distinct sites is recommended as it improves within-participant reliability. This improved sensitivity has application to clinical and research measurement of sEMG amplitude.
authors.affiliation: School of Sport, Exercise, and Health Sciences, Loughborough University, Leicestershire, LE11 3TU, UK. t.g.balshaw@lboro.ac.uk.|Institute for Sports Research, Nanyang Technological University, Singapore, Singapore. t.g.balshaw@lboro.ac.uk.|Arthritis Research UK Centre for Sport, Exercise and Osteoarthritis, Loughborough University, Leicestershire, UK. t.g.balshaw@lboro.ac.uk.
authors.forename: T G
authors.initials: TG
authors.lastname: Balshaw
authors.affiliation: School of Sport, Exercise, and Health Sciences, Loughborough University, Leicestershire, LE11 3TU, UK.
authors.forename: A
authors.initials: A
authors.lastname: Fry
authors.affiliation: School of Sport, Exercise, and Health Sciences, Loughborough University, Leicestershire, LE11 3TU, UK.|Faculty of Health and Wellbeing, Collegiate Campus, Sheffield Hallam University, Sheffield, UK.
authors.forename: T M
authors.initials: TM
authors.lastname: Maden-Wilkinson
authors.affiliation: Institute for Sports Research, Nanyang Technological University, Singapore, Singapore.|Physical Education and Sports Science Academic Group, National Institute of Education, Nanyang Technological University, Singapore, Singapore.
authors.forename: P W
authors.initials: PW
authors.lastname: Kong
authors.affiliation: School of Sport, Exercise, and Health Sciences, Loughborough University, Leicestershire, LE11 3TU, UK.|Institute for Sports Research, Nanyang Technological University, Singapore, Singapore.|Arthritis Research UK Centre for Sport, Exercise and Osteoarthritis, Loughborough University, Leicestershire, UK.
authors.forename: J P
authors.initials: JP
authors.lastname: Folland
mesh_terms: D000328:Adult; D004576:Electromyography / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D052097:Quadriceps Muscle / Q000502:physiology*
keywords: Coefficient of variation; Evoked muscle response; Intraclass correlation coefficient; Knee extension; Peripheral nerve stimulation; Voluntary muscle contraction