title: Mechanomyographic determination of post-activation potentiation in myopathies.
abstract: OBJECTIVE
  There is a need to provide an index of muscle contractility in evaluating myopathies especially in the clinical setting. This study was conducted to investigate if the mechanomyogram post-activation potentiation (MMG-PAP) can be used as an index of muscle contractile force potentiation (force-PAP), if it differs between normal and myopathic muscles, and if it can reflect abnormalities in muscle fiber anatomy.
  
  
  METHODS
  The correlation between MMG-PAP and force-PAP was evaluated in 12 normal subjects after maximum voluntary contraction (MVC) of the biceps brachii muscle. The same method was then applied to study MMG-PAP in 16 patients with myopathies, 16 disease and 25 normal controls. Mean fiber diameters and the proportions of type 1 and 2 fibers in biopsied biceps brachii muscle were determined and compared with MMG-PAP values.
  
  
  RESULTS
  There was a significant positive correlation between force-PAP (197 +/- 148%) and MMG-PAP (135 +/- 68%) immediately after MVC (P < 0.05). The mean MMG-PAP in myopathies (66 +/- 53%) was significantly lower than those of the disease (128 +/- 34%; P < 0.005) and normal controls (120 +/- 56%; P < 0.005). Patients with non-dystrophic myopathies, including those with myositis, had significantly lower MMG-PAP values (38 +/- 20%; P < 0.005) than those with muscular dystrophy (148 +/- 23%). MMG-PAP did not clearly correlate with either type 2 fiber atrophy or type 2 fiber disproportion based on muscle biopsy analysis of myopathic patients.
  
  
  CONCLUSIONS
  This study shows that MMG-PAP can be used as an index of muscle contractility and that it is significantly lower in non-dystrophic myopathies compared to normal subjects. MMG-PAP does not seem to reflect abnormal muscle fiber anatomy.
  
  
  CONCLUSIONS
  MMG-PAP may become a valuable non-invasive tool in augmenting routine clinical electrophysiologic studies especially in evaluating muscle contractility in myopathies.
authors.affiliation: Department of Neurology and Geriatrics, Graduate School of Medical and Dental Sciences, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima 890-8520, Japan.
authors.forename: A R
authors.initials: AR
authors.lastname: Ng
authors.forename: K
authors.initials: K
authors.lastname: Arimura
authors.forename: K
authors.initials: K
authors.lastname: Akataki
authors.forename: K
authors.initials: K
authors.lastname: Mita
authors.forename: I
authors.initials: I
authors.lastname: Higuchi
authors.forename: M
authors.initials: M
authors.lastname: Osame
mesh_terms: D000328:Adult; D000368:Aged; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000145:classification / Q000473:pathology / Q000502:physiology*; D009135:Muscular Diseases / Q000503:physiopathology*; D013223:Statistics as Topic