The fast twitch motor units of cat ankle flexors. 1. Tripartite classification on basis of fatigability

G. E. Goslow, W. E. Cameron, D. G. Stuart

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


The mechanical properties of 73 fast twitch units from the parallel fibered tibialis anterior (TA) muscle in 5 cats and 66 fast twitch units from the pinnately fibered extensor digitorum longus (EDL) muscle in 6 cats have been studied to test the degree to which the tripartite fatigability classification of medial gastrocnemius (MG) fast twitch units might be extended to other cat hind limb muscles. The samples from the 2 muscles contained few slow twitch units, with contraction times /s > 45 msec (6 TA units and 1 EDL unit), and this report addresses itself mainly to the distributions and absolute values of contraction time, peak tetanic tension, and fatigability of the fast twitch units. The mechanical properties of the muscle units in these architecturally dissimilar muscles were quite similar, except for mean absolute peak tetanic tension which was 1/3 greater for the EDL sample. Both fast twitch samples exhibited a broad range of tetanic tensions and fatigability. Within each population weak but significant positive correlations were found, however, between fatigability and (1) tetanic tension, and (2) peak rate of rise of tetanic tension. Evidence is presented to support the value of subdividing TA and EDL fast twitch units into FF (fast, highly fatigable), FI (fast, intermediate fatigability) and FR (fast, fatigue resistant) categories. By contrasting the fatigability distribution of the TA and EDL units to previous MG distributions, it was possible to show the value of the tripartite classification scheme for considering functional specialization both within and across the fast twitch population of different large muscles of the cat hind limb.

Original languageEnglish (US)
Pages (from-to)35-46
Number of pages12
JournalBrain research
Issue number1
StatePublished - Sep 23 1977

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology


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