Key result
Type FR motor units in rat soleus muscle had larger fibre areas and higher specific tension than type S units, with motoneurons innervating a mean of 142 fibres in FR units versus 110 in S units.
Population
Anaesthetized rats (soleus muscle motor units)
Design
Preclinical
Authors
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Rat soleus data warrant caution before clinical use; leaves open translation to human cardiac or skeletal muscle physiology.
Differences in tension generated by type FR and S units in rat soleus muscle are primarily due to differences in innervation ratio and fibre area.
Chamberlain et al. (1989) studied this question. Motor unit type (FR vs S) was evaluated on Innervation ratio and specific tension. Type FR motor units in rat soleus muscle had larger fibre areas and higher specific tension than type S units, with motoneurons innervating a mean of 142 fibres in FR units versus 110 in S units.
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