Meeting Abstract
Sloths are nearly obligatory in their use of suspensory locomotion and posture, and due to their low metabolic rate, body temperature, and rate of digestion, have an extreme need to conserve energy. It is possible that sloths possess a ‘suspensory apparatus’ analogous to that of upright ungulates, thus allowing for largely passive support of their body weight while minimizing muscle energy expenditure. The digital flexor tendons from the fore- and hindlimbs of two-toed (Choloepus hoffmanni) and three-toed (Bradypus variegatus) sloths were loaded in tension until failure with an Instron machine to test this hypothesis. Tendons displayed low tensile strength and Young’s (elastic) modulus, but had moderate stiffness indicating some compromise between strain resistance and joint position control for grip strength. Sloth flexor tendons also had elevated safety factors for suspension involving multiple limb contacts. Overall, the tendon loading curves and material properties were similar to those of generalist mammals (e.g., rats) and also match well with those of equine suspensory ‘ligaments.’ These results help explain previous findings in sloths that show low levels of muscle activation in the digital flexors among other major forelimb flexors during suspensory walking and postural hanging. Current evaluations are focused on potential modifications of increased tensile strength in the long limb bones of sloths that further indicate mechanisms that permit suspensory habits in mammals.
