Mechanical properties of diaphragm of three-toed sloth

Abstract

1. 1. The ultrastructure of the diaphragm of the South American sloth Bradypus tridactylus, which has hitherto not been studied, strongly resembled that of frog sartorius with reference to details of sarcomeric pattern and components. 2. 2. The same orderly array of actin and myosin filaments. M-line; M-line filaments, H-zones, and Z bands were noted. 3. 3. Mechanically, Hill's force-velocity ( F− V) equation fitted the force-velocity curve of this muscle very well. 4. 4. The muscle is faster than mammalian smooth muscle but slower than frog sartorius or diaphragm from the other sloth specie, Choloepus hoffmani. 5. 5. The increased curvature of the F− V curve and reduced value of a/ P o (0.113 vs 0.25 seen in the majority of mammalian striated muscles) indicate that the Bradypus muscle is more efficient than the others.