Hubel Tatjana Y, Usherwood James R
Structure and Motion Laboratory, The Royal Veterinary College, Hatfield, Hertfordshire AL9 7TA, UK.
Structure and Motion Laboratory, The Royal Veterinary College, Hatfield, Hertfordshire AL9 7TA, UK
J Exp Biol. 2015 Sep;218(Pt 18):2830-9. doi: 10.1242/jeb.122135.
Terrestrial locomotion on legs is energetically expensive. Compared with cycling, or with locomotion in swimming or flying animals, walking and running are highly uneconomical. Legged gaits that minimise mechanical work have previously been identified and broadly match walking and running at appropriate speeds. Furthermore, the 'cost of muscle force' approaches are effective in relating locomotion kinetics to metabolic cost. However, few accounts have been made for why animals deviate from either work-minimising or muscle-force-minimising strategies. Also, there is no current mechanistic account for the scaling of locomotion kinetics with animal size and speed. Here, we report measurements of ground reaction forces in walking children and adult humans, and their stance durations during running. We find that many aspects of gait kinetics and kinematics scale with speed and size in a manner that is consistent with minimising muscle activation required for the more demanding between mechanical work and power: spreading the duration of muscle action reduces activation requirements for power, at the cost of greater work demands. Mechanical work is relatively more demanding for larger bipeds--adult humans--accounting for their symmetrical M-shaped vertical force traces in walking, and relatively brief stance durations in running compared with smaller bipeds--children. The gaits of small children, and the greater deviation of their mechanics from work-minimising strategies, may be understood as appropriate for their scale, not merely as immature, incompletely developed and energetically sub-optimal versions of adult gaits.
腿部的陆地运动在能量消耗上很大。与骑自行车相比，或者与游泳或飞行动物的运动相比，行走和奔跑的经济性很低。先前已经确定了使机械功最小化的腿部步态，并且这些步态在适当速度下与行走和奔跑大致匹配。此外，“肌肉力量成本”方法在将运动动力学与代谢成本联系起来方面很有效。然而，很少有人解释动物为何偏离使功最小化或使肌肉力量最小化的策略。而且，目前还没有关于运动动力学如何随动物大小和速度缩放的机制性解释。在这里，我们报告了对行走儿童和成年人的地面反作用力及其跑步时支撑时间的测量结果。我们发现，步态动力学和运动学的许多方面随速度和大小的缩放方式与使机械功和功率要求更高的情况下所需的肌肉激活最小化相一致：延长肌肉作用时间会降低功率的激活要求，但代价是功的需求增加。对于较大的两足动物——成年人——机械功的要求相对更高，这解释了他们行走时对称的M形垂直力轨迹，以及与较小的两足动物——儿童——相比跑步时相对较短的支撑时间。幼儿的步态，以及他们的力学与使功最小化策略的更大偏差，可能被理解为适合他们的体型，而不仅仅是成人步态的不成熟、未完全发育和能量次优版本。
