Tonicity physiological properties

Physiologically, type-1 fibers are considered to be slow-twitch and rather fatigne-resistant, while the type-2 fibers are fast-twitch and fast-fatiguing, as found in normal mammalian muscle [22, 23] and corroborated in human muscle [24, 25]. The designations slow-twitch and fast-twitch were introduced [4, 8, 9, 26] to distinguish the twitch properties of mammalian twitch-muscle fibers from amphibian non-twitch, extremely slow tonic fibers of the thigh adductor clasp muscles. 

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