title: Loss of motor unit size and quadriceps strength over 10 years in post-polio syndrome.
abstract: OBJECTIVE
  To investigate whether strength decline in post-polio syndrome (PPS) results from excessive distal axonal degeneration of enlarged motor units.
  
  
  METHODS
  We assessed changes over 10 years in isometric quadriceps strength, mean motor unit action potential (MUAP) size, root mean squared (RMS) amplitude, and level of interference (LOI) in 47 patients with PPS and 12 healthy controls, using high density surface EMG. At baseline, all patients had symptomatic quadriceps dysfunction, evidenced by transmission defects on single-fibre EMG.
  
  
  RESULTS
  MU size and strength declined significantly by 20% and 15%, respectively in patients with PPS. Those with the largest initial MU sizes exhibited the greatest losses of mean MU size (27%) and proportional decreases in quadriceps strength (23%). Initial strength, change in LOI and change in RMS amplitude together explained 35% of the variability in strength changes in patients. MU size of controls did not change, although they lost 29% strength.
  
  
  CONCLUSIONS
  MU size and strength declined concomitantly in a homogeneous cohort of patients with PPS and quadriceps dysfunction.
  
  
  CONCLUSIONS
  This long term follow-up study provides evidence that size diminution of enlarged MUs combined with a reduced number of active MUs contributes to the gradual strength decline in PPS.
authors.affiliation: Department of Rehabilitation, Academic Medical Center (AMC), Postbus 22660, 1100 DD Amsterdam, The Netherlands. Electronic address: a.bickerstaffe@amc.uva.nl.
authors.forename: A
authors.initials: A
authors.lastname: Bickerstaffe
authors.affiliation: Radboud University Nijmegen Medical Centre, Donders Institute for Brain, Cognition and Behaviour, Department of Neurology/Clinical Neurophysiology, Postbus 910, 6500 HB Nijmegen, The Netherlands; Epilepsy Centre Kempenhaeghe, Postbus 61, 5590 AB Heeze, The Netherlands. Electronic address: dijkh@kempenhaeghe.nl.
authors.forename: J P
authors.initials: JP
authors.lastname: van Dijk
authors.affiliation: Department of Rehabilitation, Academic Medical Center (AMC), Postbus 22660, 1100 DD Amsterdam, The Netherlands. Electronic address: j.a.beelen@amc.nl.
authors.forename: A
authors.initials: A
authors.lastname: Beelen
authors.affiliation: Epilepsy Centre Kempenhaeghe, Postbus 61, 5590 AB Heeze, The Netherlands. Electronic address: ZwartsM@kempenhaeghe.nl.
authors.forename: M J
authors.initials: MJ
authors.lastname: Zwarts
authors.affiliation: Department of Rehabilitation, Academic Medical Center (AMC), Postbus 22660, 1100 DD Amsterdam, The Netherlands. Electronic address: f.nollet@amc.nl.
authors.forename: F
authors.initials: F
authors.lastname: Nollet
mesh_terms: D000200:Action Potentials; D000328:Adult; D000818:Animals; D015331:Cohort Studies; D004576:Electromyography; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D051379:Mice; D008875:Middle Aged; D009046:Motor Neurons / Q000473:pathology*; D009119:Muscle Contraction / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology*; D009410:Nerve Degeneration / Q000473:pathology / Q000503:physiopathology; D016262:Postpoliomyelitis Syndrome / Q000473:pathology* / Q000503:physiopathology*; D011446:Prospective Studies; D052097:Quadriceps Muscle / Q000503:physiopathology*; D055948:Sarcopenia / Q000473:pathology / Q000503:physiopathology
keywords: High-density surface EMG; Motor unit size; Post-polio syndrome; Prospective cohort study; Quadriceps strength