Force and fatigue in human type I muscle fibres. A surface EMG study in patients with congenital myopathy and type I fibre predominance.
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.
Institute of Neurology, University of Nijmegen, The Netherlands.
W H
WH
Linssen
D F
DF
Stegeman
E M
EM
Joosten
H J
HJ
Merks
H J
HJ
ter Laak
R A
RA
Binkhorst
S L
SL
Notermans
D000328:Adult; D001132:Arm; D004576:Electromyography; D015444:Exercise; D005221:Fatigue / Q000503:physiopathology; D005260:Female; D006801:Humans; D007511:Ischemia / Q000503:physiopathology; D008297:Male; D009132:Muscles / Q000098:blood supply / Q000473:pathology / Q000503:physiopathology*; D009135:Muscular Diseases / Q000151:congenital / Q000473:pathology / Q000503:physiopathology*