Abstract
AbstractBecause sloths are among the slowest moving of mammals, it is of interest to determine whether the rate limiting factor is in their motivation, central nervous system, or their muscles.Muscle characteristics of ten sloths (Choloepus hoffmanni and Bradypus tridactylus) were studied by neuromuscular examination, electrophysiological, biochemical, and histological methods. Muscle twitch contraction averages 120 msec and one‐half relaxation time was 108 msec. Muscle contraction and relaxation are extremely sensitive to cold but were unaltered by calcium, quinine or procaine amide.Biochemical studies showed ATPase activity to be extremely low.Ultrastructure conformed closely to that of mammalian twitch fibers.Our data suggest that although muscle mechanics undoubtedly contribute to the slow movements of the sloth, they are not the only rate limiting factor.
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