Editing Muscular hydrostat (section)

===Torsion===
Torsion is the twisting of a muscular hydrostat along its long axis and is produced by a helical or oblique arrangement of musculature<ref name=Kier1985>{{Cite journal | last1 = Kier | first1 = W. M. | title = The musculature of squid arms and tentacles: Ultrastructural evidence for functional differences | doi = 10.1002/jmor.1051850208 | journal = Journal of Morphology | volume = 185 | issue = 2 | pages = 223–239| year = 1985 | pmid = 30011972 | s2cid = 51631466 }}</ref> which have varying direction. For a counter-clockwise torsion it is necessary for a right-hand helix to contract. Contraction of a left-hand helix causes clockwise torsion. The simultaneous contraction of both right and left-hand helixes results in an increase in resistance to torsional forces. The oblique or helical muscle arrays in the muscular hydrostats are located in the periphery of the structure, wrapping the inner core of musculature, and this peripheral location provides a larger moment through which the torque is applied than a more central location. The effect of helically arranged muscle fibers, which may also contribute to changes in length of a muscular hydrostat, depends on fiber angle—the angle that the helical muscle fibers make with the long axis of the structure.

The length of the helical fiber is at a minimum when the fiber angle equals 54°44′ and is at maximum length when the fiber angle approaches 0° and 90°.<ref name=Kier1985 /> Summed up, this means that helically arranged muscle fibers with a fiber angle greater than 54°44′ will create force for both torsion and elongation while helically arranged muscle fibers with a fiber angle less than 54°44′ will create force for both torsion and shortening.<ref>Meyers, J. J.; O'Reilly, J. C.; Monroy, J. A.; Nishikawa, K. C. (2004). "[http://jeb.biologists.org/content/207/1/21.full Mechanism of tongue protraction in microhylid frogs]. ''The Journal of Experimental Biology'' '''207''': 21–31.</ref> The fiber angle of the oblique or helical muscle layers must increase during shortening and decrease during lengthening. In addition to creating a torsional force, the oblique muscle layers will therefore create a force for elongation that may aid the transverse musculature in resisting longitudinal compression.