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Motor unit organization of human medial gastrocnemius.
Author(s) -
Garnett R A,
O'Donovan M J,
Stephens J A,
Taylor A
Publication year - 1979
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1979.sp012643
Subject(s) - microstimulation , motor unit , gastrocnemius muscle , anatomy , motor unit recruitment , glycogen , chemistry , fibre type , muscle biopsy , biology , endocrinology , medicine , neuroscience , biopsy , electromyography , biochemistry , skeletal muscle , stimulation
1. The properties of fifty‐seven motor units in human medial gastrocnemius have been studied using controlled intramuscular microstimulation, glycogen depletion and muscle biopsy. 2. Motor units could be divided into three classes on the basis of their mechanical properties. Type S units were slow, small and fatigue resistant. Type FR units were fast, intermediate in size, and fatigue resistant. Type FF units were fast, large and fatigable. 3. Glycogen depletion of a number of type S and FF units revealed them to be composed of type 1 and type 2b muscle fibres respectively. 4. The results suggest that during slowly increasing voluntary contractions where units are recruited in order of size, type 1 and 2a muscle fibres would be employed at low force levels followed by type 2b muscle fibres in stronger contractions.