Ren Lei, Butler Melanie, Miller Charlotte, Paxton Heather, Schwerda Delf, Fischer Martin S, Hutchinson John R
Structure and Motion Laboratory, Department of Veterinary Basic Sciences, The Royal Veterinary College, University of London, Hatfield, Hertfordshire AL9 7TA, UK.
J Exp Biol. 2008 Sep;211(Pt 17):2735-51. doi: 10.1242/jeb.018820.
As the largest extant terrestrial animals, elephants do not trot or gallop but can move smoothly to faster speeds without markedly changing their kinematics, yet with a shift from vaulting to bouncing kinetics. To understand this unusual mechanism, we quantified the forelimb and hindlimb motions of eight Asian elephants (Elephas maximus) and seven African elephants (Loxodonta africana). We used 240 Hz motion analysis (tracking 10 joint markers) to measure the flexion/extension angles and angular velocities of the limb segments and joints for 288 strides across an eightfold range of speeds (0.6-4.9 m s(-1)) and a sevenfold range of body mass (521-3684 kg). We show that the columnar limb orientation that elephants supposedly exemplify is an oversimplification--few segments or joints are extremely vertical during weight support (especially at faster speeds), and joint flexion during the swing phase is considerable. The 'inflexible' ankle is shown to have potentially spring-like motion, unlike the highly flexible wrist, which ironically is more static during support. Elephants use approximately 31-77% of their maximal joint ranges of motion during rapid locomotion, with this fraction increasing distally in the limbs, a trend observed in some other running animals. All angular velocities decrease with increasing size, whereas smaller elephant limbs are not markedly more flexed than adults. We find no major quantitative differences between African and Asian elephant locomotion but show that elephant limb motions are more similar to those of smaller animals, including humans and horses, than commonly recognized. Such similarities have been obscured by the reliance on the term ;columnar' to differentiate elephant limb posture from that of other animals. Our database will be helpful for identifying elephants with unusual limb movements, facilitating early recognition of musculoskeletal pathology.
作为现存最大的陆生动物，大象不会小跑或疾驰，但能平稳地加速到更快速度，且运动学特征没有明显变化，不过动力学上会从跳跃转变为弹跳。为了解这种独特机制，我们对八头亚洲象（印度象）和七头非洲象（非洲象）的前肢和后肢运动进行了量化。我们使用240赫兹的运动分析（追踪10个关节标记点），在0.6至4.9米每秒的八倍速度范围和521至3684千克的七倍体重范围内，测量了288步中肢体节段和关节的屈伸角度及角速度。我们发现，大象被认为所代表的柱状肢体姿态过于简化——在承重时很少有节段或关节是极度垂直的（尤其是在较快速度时），而且摆动阶段的关节弯曲幅度相当大。结果表明，“僵硬”的脚踝具有类似弹簧的运动，而高度灵活的手腕在支撑时反而更静止，这颇具讽刺意味。大象在快速移动时使用其最大关节活动范围的约31%至77%，这一比例在肢体远端逐渐增加，在其他一些奔跑动物中也观察到了这种趋势。所有角速度都随体型增大而降低，而小象的肢体弯曲程度并不比成年象明显更大。我们发现非洲象和亚洲象的运动在数量上没有重大差异，但表明大象的肢体运动与包括人类和马在内的较小动物的肢体运动比通常认为的更为相似。这种相似性因依赖“柱状体”一词来区分大象与其他动物的肢体姿态而被掩盖。我们的数据库将有助于识别肢体运动异常的大象，便于早期发现肌肉骨骼疾病。
