Young Melody W, McKamy Andrew J, Dickinson Edwin, Yarbro Johnathan, Ragupathi Ashwin, Guru Navjot, Avey-Arroyo Judy A, Butcher Michael T, Granatosky Michael C
Department of Anatomy, New York Institute of Technology College of Osteopathic Medicine, Old Westbury, New York, USA.
Department of Biological Sciences, Youngstown State University, Youngstown, Ohio, USA.
J Exp Zool A Ecol Integr Physiol. 2023 May;339(4):383-397. doi: 10.1002/jez.2684. Epub 2023 Feb 6.
Living sloths exhibit numerous anatomical specializations towards inverted quadrupedalism, however, previous studies have noted a more varied locomotor repertoire than previously anticipated. In this study, we present spatiotemporal gait characteristics and triaxial kinetic data from the brown-throated three-toed sloth (Bradypus variegatus) across three locomotor modes: terrestrial quadrupedal "crawling", suspensory walking, and vertical climbing. Compared to quadrupedal crawling and suspensory walking, B. variegatus adopted longer contact times and stride durations, larger duty factors, and greater speed during vertical climbing. Net fore-aft impulses were significantly greater during vertical climbing in both limb pairs than in quadrupedal crawling and suspensory walking. Functionally, during quadrupedal crawling and vertical climbing, both limb pairs served propulsive roles, while differentiation between a propulsive forelimb and braking hindlimb was observed during suspension. Net tangential forces differentiated vertical climbing kinetics from the other modes of locomotion, with the introduction of bidirectional pulling and pushing forces in the forelimb and hindlimb, respectively. The net mediolateral impulses were similar in vertical climbing and quadrupedal crawling as both limb pairs directed forces in one direction, whereas during suspensory walking, the laterally dominant forelimb was opposed by the medially dominant hindlimb. In total, this study provides novel data on the diverse locomotor dynamics in a slow-moving arboreal tetrapod and posits new testable hypotheses about the neuroplasticity and ease of transitioning between locomotor behaviors. The strikingly similar kinetic profiles of quadrupedal crawling and suspensory walking compared to vertical climbing suggest shared neuromuscular and mechanical demands between these mirrored locomotor modes.
现存的树懒在解剖学上表现出许多适应倒转四足行走的特征，然而，先前的研究已经注意到其运动方式比之前预期的更加多样。在本研究中，我们展示了褐喉三趾树懒（Bradypus variegatus）在三种运动模式下的时空步态特征和三轴动力学数据：陆地四足“爬行”、悬垂行走和垂直攀爬。与四足爬行和悬垂行走相比，褐喉三趾树懒在垂直攀爬时采用了更长的接触时间和步幅持续时间、更大的 duty 因子以及更快的速度。在垂直攀爬过程中，两对肢体的前后净冲量均显著大于四足爬行和悬垂行走时。在功能上，在四足爬行和垂直攀爬过程中，两对肢体都起到推进作用，而在悬垂过程中观察到前肢推进和后肢制动的分化。净切向力将垂直攀爬的动力学与其他运动模式区分开来，在前肢和后肢分别引入了双向的拉力和推力。垂直攀爬和四足爬行时的内外侧净冲量相似，因为两对肢体都向一个方向施加力，而在悬垂行走时，外侧占主导的前肢与内侧占主导的后肢相互对抗。总的来说，本研究提供了关于一种行动缓慢的树栖四足动物多样运动动力学的新数据，并提出了关于神经可塑性以及运动行为之间转换难易程度的新的可测试假设。与垂直攀爬相比，四足爬行和悬垂行走惊人地相似的动力学特征表明，这些镜像运动模式之间存在共同的神经肌肉和机械需求。
