Force and fatigue in human type I muscle fibres. A surface EMG study in patients with congenital myopathy and type I fibre predominance

Brain. 1991 Oct:114 ( Pt 5):2123-32. doi: 10.1093/brain/114.5.2123.

Abstract

An isometric ischaemic intermittent m.biceps brachii exercise test is performed by 4 patients suffering from congenital myopathies which are characterized by a 100% type I fibre predominance, and by 26 healthy volunteers. Thirty contractions per minute are made at an 80% of maximal voluntary contraction level. It is found that type I muscle fibres have a fourfold lower force-generating capacity than type II muscle fibres. The EMG amplitude shows that more EMG voltage is needed per unit force in the patients with 100% type I fibres compared with controls. Under standardized fatiguing circumstances the power density frequency spectrum shows a weaker shift to lower frequencies in patients with 100% type I muscle fibres compared with controls. The muscle fibre conduction velocity (MFCV) of type I muscle fibres shows no decline during ischaemic exercise indicating an unimpaired muscle membrane excitability.

MeSH terms

  • Adult
  • Arm
  • Electromyography*
  • Exercise
  • Fatigue / physiopathology
  • Female
  • Humans
  • Ischemia / physiopathology
  • Male
  • Muscles / blood supply
  • Muscles / pathology
  • Muscles / physiopathology*
  • Muscular Diseases / congenital
  • Muscular Diseases / pathology
  • Muscular Diseases / physiopathology*