Low effective mechanical advantage of giraffes' limbs during walking reveals trade-off between limb length and locomotor performance
Low effective mechanical advantage of giraffes' limbs during walking reveals trade-off between limb length and locomotor performance
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长颈鹿四肢在行走过程中的低有效机械优势揭示了四肢长度和运动性能之间的权衡
DOI：
10.1101/2021.04.29.441773
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Basu C
中科院分区：
文献类型：
--
作者：
Basu C
长颈鹿(Giraffa Camelopardalis)具有特殊的运动形态，即细长而纤细的远端肢体。虽然这有助于它们的整体身高，并改善它们的摄食行为，但我们认为，与其他卷曲哺乳动物相比，长肢节段和适度的肌肉杠杆臂的组合导致较低的有效机械优势(EMA，杠杆内力矩臂与外杠杆力矩臂的比率)。为了验证这一点，我们使用了实验测量的运动学和地面反作用力(GRF)、肌肉骨骼建模和反向动力学相结合的方法来计算长颈鹿行走时的前肢EMA。长颈鹿行走的EMA为0.34(±0.05SD)，与其行走步态中的速度没有明显关联。长颈鹿的EMA比其他哺乳动物的预期低约四倍，从0.03公斤到297公斤不等，这提供了进一步的证据，表明超过马的哺乳动物的EMA处于平台期，甚至减少。我们通过对灭绝的巨型长颈鹿和另一种现存的长颈鹿Okapia johnstoni的GRF和肌力矩臂进行建模，进一步检验了肢体节段长度是决定EMA的一个因素。长颈鹿和俄克拉皮亚人的EMA相似，尽管体重相差4到6倍(OkapiaEMA=0.38)。相比之下，Sivatherium与长颈鹿有着相似的身体质量，EMA(0.59)更高，我们认为这反映了行为差异，例如运动表现能力有所增强。我们的建模方法表明，肢体长度是GRF力矩臂大小的决定因素，除非肌肉力矩臂的比例与肢体长度等距，否则高个子哺乳动物倾向于低EMA。
Giraffes (Giraffa camelopardalis) possess specialized locomotor morphology, namely elongate and gracile distal limbs. While this contributes to their overall height and enhances feeding behavior, we propose that the combination of long limb segments and modest muscle lever arms results in low effective mechanical advantage (EMA, the ratio of in-lever to out-lever moment arms), when compared with other cursorial mammals. To test this, we used a combination of experimentally measured kinematics and ground reaction forces (GRFs), musculoskeletal modeling, and inverse dynamics to calculate giraffe forelimb EMA during walking. Giraffes walk with an EMA of 0.34 (±0.05 SD), with no evident association with speed within their walking gait. Giraffe EMA was about four times lower than expectations extrapolated from other mammals, ranging from 0.03 to 297 kg, and this provides further evidence that EMA plateaus or even diminishes in mammals exceeding horse size. We further tested the idea that limb segment length is a factor which determines EMA, by modeling the GRF and muscle moment arms in the extinct giraffidSivatherium giganteumand the other extant giraffid,Okapia johnstoni. GiraffaandOkapiashared similar EMA, despite a four to sixfold difference in body mass (OkapiaEMA = 0.38). In contrast,Sivatherium,sharing a similar body mass withGiraffa,had greater EMA (0.59), which we propose reflects behavioral differences, such as a somewhat increased capability for athletic performance. Our modeling approach suggests that limb length is a determinant of GRF moment arm magnitude and that unless muscle moment arms scale isometrically with limb length, tall mammals are prone to low EMA.