Dutto Darren J, Hoyt Donald F, Clayton Hilary M, Cogger Edward A, Wickler Steven J
School of Physical Education and Health, Eastern Oregon University, La Grande, OR 97850, USA.
J Exp Biol. 2006 Oct;209(Pt 20):3990-9. doi: 10.1242/jeb.02471.
The net work of the limbs during constant speed over level ground should be zero. However, the partitioning of negative and positive work between the fore- and hindlimbs of a quadruped is not likely to be equal because the forelimb produces a net braking force while the hindlimb produces a net propulsive force. It was hypothesized that the forelimb would do net negative work while the hindlimb did net positive work during trotting in the horse. Because vertical and horizontal impulses remain unchanged across speeds it was hypothesized that net work of both limbs would be independent of speed. Additionally because the major mass of limb musculature is located proximally, it was hypothesized that proximal joints would do more work than distal joints. Kinetic and kinematic analysis were combined using inverse dynamics to calculate work and power for each joint of horses trotting at between 2.5 and 5.0 m s(-1). Work done by the hindlimb was indeed positive (consistently 0.34 J kg(-1) across all speeds), but, contrary to our hypothesis, net work by the forelimb was essentially zero (but also independent of trotting speed). The zero net work of the forelimb may be the consequence of our not being able to account, experimentally, for the negative work done by the extrinsic muscles connecting the scapula and the thorax. The distal three joints of both limbs behaved elastically with a period of energy absorption followed by energy return. Proximal forelimb joints (elbow and shoulder) did no net work, because there was very little movement of the elbow and shoulder during the portion of stance when an extensor moment was greatest. Of the two proximal hindlimb joints, the hip did positive work during the stride, generating energy almost throughout stance. The knee did some work, but like the forelimb proximal joints, had little movement during the middle of stance when the flexion moment was the greatest, probably serving to allow the efficient transmission of energy from the hip musculature to the ground.
在水平地面上以恒定速度运动时，四肢的净功应为零。然而，四足动物前肢和后肢之间正负功的分配不太可能相等，因为前肢产生净制动力而后肢产生净推进力。据推测，在马小跑时，前肢做净负功而后肢做净正功。由于垂直和水平冲量在不同速度下保持不变，因此推测四肢的净功与速度无关。此外，由于肢体肌肉组织的主要质量位于近端，因此推测近端关节比远端关节做的功更多。利用逆动力学将动力学和运动学分析相结合，计算了速度在2.5至5.0米每秒之间小跑的马的每个关节的功和功率。后肢所做的功确实为正（在所有速度下均始终为0.34焦耳每千克），但与我们的假设相反，前肢的净功基本为零（但也与小跑速度无关）。前肢净功为零可能是因为我们在实验中无法考虑连接肩胛骨和胸部的外部肌肉所做的负功。四肢的远端三个关节表现出弹性，有一个能量吸收期，随后是能量返回期。前肢近端关节（肘部和肩部）没有净功，因为在伸展力矩最大的站立阶段，肘部和肩部的运动非常小。在两个后肢近端关节中，髋关节在步幅中做正功，几乎在整个站立阶段都产生能量。膝关节做了一些功，但与前肢近端关节一样，在站立中期屈曲力矩最大时运动很小，可能是为了使能量从前部肌肉有效地传递到地面。
