title: Reverse fiber type disproportion: A distinct metabolic myopathy.
abstract: In this investigation we characterized the physiological and metabolic responses to incremental exercise in 13 subjects with a predominance of type II fibers on muscle biopsy.
  
  
  
  Subjects underwent incremental exercise testing with measures of maximum oxygen uptake ( V˙O2 max), maximum heart rate (fc max), chronotropic index (fc / V˙O2 slope), maximum ventilation ( V˙emax), blood lactate, ammonia, and creatine kinase (CK) levels. Muscle fiber type was determined by myosin ATPase histochemistry.
  
  
  
  Muscle biopsies showed more type II fibers (75%) in subjects compared with normal individuals (P < 0.01). Subjects exhibited normal V˙O2 max and end-exercise lactate, whereas ammonia and CK levels at maximum exercise were significantly higher.
  
  
  
  Subjects with type II muscle fiber predominance exhibited exaggerated increases in ammonia and elevated CK levels during exercise. Predominance of type II fibers on muscle biopsy is the opposite finding of congenital fiber type disproportion; we suggest these patients be referred to as having "reverse fiber type disproportion." Muscle Nerve 54: 86-93, 2016.
authors.affiliation: Department of Medicine, UCLA Exercise Physiology Research Laboratory, David Geffen School of Medicine, University of California, Los Angeles, 10833 Le Conte Avenue, 37-131 CHS, Los Angeles, California, 90095, USA.|Department of Physiology, UCLA Exercise Physiology Research Laboratory, David Geffen School of Medicine, University of California, Department of Medicine, Los Angeles, Los Angeles, California, USA.
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Cooper
authors.affiliation: Department of Medicine, UCLA Exercise Physiology Research Laboratory, David Geffen School of Medicine, University of California, Los Angeles, 10833 Le Conte Avenue, 37-131 CHS, Los Angeles, California, 90095, USA.|Department of Physiology, UCLA Exercise Physiology Research Laboratory, David Geffen School of Medicine, University of California, Department of Medicine, Los Angeles, Los Angeles, California, USA.
authors.forename: Brett A
authors.initials: BA
authors.lastname: Dolezal
authors.affiliation: Queen's University, Belfast, Northern Ireland, UK.
authors.forename: Marshall
authors.initials: M
authors.lastname: Riley
authors.affiliation: Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, USA.
authors.forename: M Anthony
authors.initials: MA
authors.lastname: Verity
authors.affiliation: Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, USA.
authors.forename: Perry B
authors.initials: PB
authors.lastname: Shieh
mesh_terms: D000293:Adolescent; D000328:Adult; D000641:Ammonia / Q000097:blood; D001706:Biopsy; D003402:Creatine Kinase / Q000097:blood; D015444:Exercise / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D008875:Middle Aged; D018763:Muscle Fatigue / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000473:pathology*; D018482:Muscle, Skeletal / Q000378:metabolism; D020914:Myopathies, Structural, Congenital / Q000473:pathology* / Q000503:physiopathology*; D010101:Oxygen Consumption / Q000502:physiology; D011659:Pulmonary Gas Exchange; D012189:Retrospective Studies; D014691:Ventilation
chemical_list: D019344:Lactic Acid; D000641:Ammonia; D003402:Creatine Kinase
keywords: ammonia; exercise; lactate; muscle fiber; type II