Department of Anatomy, New York Institute of Technology College of Osteopathic Medicine, Old Westbury, New York, USA.
Center for Biomedical Innovation, New York Institute of Technology College of Osteopathic Medicine, Old Westbury, New York, USA.
J Exp Zool A Ecol Integr Physiol. 2022 Aug;337(7):699-708. doi: 10.1002/jez.2605. Epub 2022 May 12.
A key characteristic of primate above-branch arboreal locomotion is hindlimb-biased weight support, subverting the typical mammalian condition in which the majority of the body weight is supported by the forelimb. This shift is thought to reflect an adaptation toward the arboreal niches exploited by early primates. However, above-branch quadrupedalism represents only one locomotor mode employed by primates in arboreal contexts. Inverted quadrupedal gaits, in which primates are suspended beneath branches by their hands and feet, have been documented in more than 50 primate taxa. This gait is characterized by a return to forelimb-biased weight distributions and a transition from peak vertical forces being greatest in the hindlimb to being greatest in the forelimb, which may occur to protect the hindlimb from high magnitudes of tensile loading when inverted. In this study, we compare kinetic and kinematic data during upright and inverted quadrupedalism in Lemur catta, Varecia variegata, Cebus capucinus, and Saimiri sciureus. These data are referenced against a classical inverted quadrupedal model: the two-toed sloth (Choloepus didactylus). Our findings show that inverted quadrupedalism in primates is differentiated from above-branch quadrupedalism by increases in forelimb weight support, forelimb contact times, and both forelimb and hindlimb joint excursions. Previously postulated biomechanical models outlining mechanisms relating to the control of weight support during upright walking do not translate well to inverted quadrupedal walking. We suggest that inverted primates may simply be adopting basal neuromuscular gait characteristics and applying them facultatively to this infrequent locomotor behavior.
灵长类动物树栖上方四肢运动的一个关键特征是后肢偏向的重量支撑，颠覆了典型的哺乳动物状态，即大部分体重由前肢支撑。这种转变被认为反映了早期灵长类动物对树栖生态位的适应。然而，上方树枝的四足运动只是灵长类动物在树栖环境中采用的一种运动模式。倒悬四足步态，即灵长类动物用手和脚悬挂在树枝下，已经在 50 多种灵长类动物中被记录下来。这种步态的特点是恢复了前肢偏向的重量分布，并且从后腿承受最大垂直力转变为前腿承受最大垂直力，这可能是为了防止后腿受到倒置时高拉伸载荷的影响。在这项研究中，我们比较了懒猴（Lemur catta）、环尾狐猴（Varecia variegata）、卷尾猴（Cebus capucinus）和松鼠猴（Saimiri sciureus）在直立和倒悬四足运动中的运动学和运动学数据。这些数据与经典的倒悬四足模型（二趾树懒（Choloepus didactylus））进行了对比。我们的研究结果表明，灵长类动物的倒悬四足运动与上方树枝四足运动的区别在于前肢重量支撑、前肢接触时间以及前肢和后肢关节的运动幅度增加。先前提出的生物力学模型概述了与直立行走时控制体重支撑相关的机制，但这些模型不能很好地转化为倒悬四足行走。我们认为，倒悬的灵长类动物可能只是采用了基础的神经肌肉步态特征，并将其灵活地应用于这种不常见的运动行为。
