Mechanics and energetics of stable bipedal locomotion in uneven terrain: Does a trade-off exist between economy and stability?

对人类和鸟类行走和奔跑的研究表明，尽管腿的解剖结构不同，但所有两条腿的动物(两足动物)在平地上的移动方式都相似。这一发现为经济步行和跑步带来了极其简单的理论模型。这些模型激发了技术进步，如最快的跑道，最经济的两足机器人，以及简单的假肢设备，包括田径运动员奥斯卡·皮斯托瑞斯佩戴的猎豹Flex-Foot。尽管取得了这些进步，但能够在不平坦的地形上既稳定又经济地移动的假肢的设计仍然是一个挑战。在自然地形上行走和跑步，需要经常调整颠簸、台阶、洞和障碍物。然而，目前用于人类运动的假肢在不平坦的地形上表现不佳。虽然奥斯卡·皮斯托瑞斯佩戴的柔足假肢非常经济，可以跑很长的距离，但它不会根据路缘或楼梯等地形的变化进行调整。电动假肢等先进设备可以提高在崎岖地形中的机动性，但目前用途有限，因为它们消耗太多能源，电池电量很快就会耗尽。新的假肢和其他在不同地形下表现良好的活动辅助设备可以极大地改善行动不便的人的生活质量，包括截肢者和有跌倒风险的老年人。与这些技术相比，人类和鸟类在不同的地形上实现了显著的稳定性和经济性。然而，我们对他们如何做到这一点知之甚少。目前的行走和跑步模型大多基于对在完全平坦、均匀的地形(如跑道或跑步机)上运动的研究，而这些地形在自然界中很少存在。长期以来，人们一直认为，在经济和运动稳定性之间存在权衡。这个想法从来没有被检验过，因为关于走路和跑步稳定性的研究太少了。这个项目将通过比较六种地面鸟类的稳定策略和移动的能量成本来解决这个问题。我们将测量鸟儿在不平坦的地形条件下行走和奔跑时的力学、稳定性和能源成本。这将揭示两足动物如何根据地形条件、速度和步态在不同的移动策略中进行选择。地面鸟是这项研究的理想研究动物，因为它们是多样化的两足动物，生活在广泛的栖息地，体型范围很大：从100克以下的鹌鹑到100公斤以上的鸵鸟。通过对地面鸟类的研究，该项目将开发适用于广泛动物和地形条件的稳定的两足动物运动的简单模型。这些模型将揭示稳定性和经济性的基本原则，这些原则可能直接影响假肢、矫形器和腿部机器人的设计。一个重要的观察是，小鸟以蹲伏、弯曲腿的姿势行走和奔跑，而大型鸟类以相对笔直的腿姿势移动。腿部姿势和解剖结构的差异可能反映了小鸟对稳定性的更大适应以及大型鸟类的经济性。对于在同一地形上移动的小型和大型动物，地形高度的任何变化都将是小型动物腿部长度的较大部分。因此，对于小动物来说，世界是一个相对“粗糙”的地方，需要强大的稳定性。该项目将比较小鸟和大鸟使用的稳定策略，并确定小鸟是否更稳定。这项研究将揭示两足动物如何在不平的地形上行走和奔跑，而不会摔倒或受伤。没有跌倒和受伤的行动能力对于年老和步态受损的人的健康尤为重要。这些发现可能会对这些领域产生重大影响，激励人们在预防人类跌倒、步态康复以及假肢、矫形器和其他活动辅助设备的设计方面进行创新。

Studies of walking and running in humans and birds have revealed that all two legged animals (bipeds) move in similar ways over level ground, despite differences in leg anatomy. This finding has led to elegantly simple theoretical models for economic walking and running. These models have inspired technological advances such as the fastest running tracks, the most economic bipedal robots, and simple prosthetics devices, including the Cheetah Flex-Foot worn by track athlete Oscar Pistorious. Despite these advances, the design of prosthetics that can move with both stability and economy over uneven terrain remains a challenge. Walking and running in natural terrain requires frequent adjustment for bumps, steps, holes and obstacles. Yet, current prosthetic devices for human locomotion perform poorly over uneven terrain. Although the flex-foot prosthetic worn by Oscar Pistorious provides high economy, allowing him to run long distances, it does not adjust for variations in terrain such as kerbs or stairs. Advances such as motorised prosthetic devices can improve mobility in uneven terrain, but currently have limited use because they consume too much energy and run out of battery power quickly. New prosthetics and other mobility aids that perform well in varied terrain could vastly improve quality of life for those with limited mobility, including amputees and ageing individuals at risk for falls. In comparison to these technologies, humans and birds achieve remarkable stability and economy of movement in varied terrain. However, we understand very little about how they accomplish this. Current models of walking and running are based mostly on studies of movement over completely smooth, uniform terrain (such as a track or treadmill), which rarely exist in nature. It has long been supposed that a trade-off exists between economy and stability of locomotion. This idea has never been tested because so little research exists on stability of walking and running. This project will address this problem by by comparing stabilising strategies and energy cost of locomotion among six species of ground birds. We will measure mechanics, stability and energetic cost as birds walk and run over uneven terrain conditions. This will reveal how bipeds choose among different movement strategies depending on terrain condition, speed and gait. Ground birds are ideal study animals for this research because they are diverse bipedal athletes, live in broad range of habitats, and span a large size range: from quail under 100 grams to ostrich over 100 kilograms. Through study of ground birds, this project will develop simple models for stable bipedal locomotion that apply to a broad range of animals and terrain conditions. The models will reveal basic principles for stability and economy that could directly impact upon the design of prosthetics, orthotics and legged robots. One important observation is that small birds walk and run with a crouched, bent-leg posture, and large birds move with a relatively straight-leg posture. The difference in leg posture and anatomy likely reflects greater adaptation for stability in small birds and economy in large birds. For small and large animals moving in the same terrain, any change in terrain height will be a larger fraction of a small animal's leg length. Consequently, the world is a relatively 'rough' place for small animals, requiring robust stability. This project will compare stability strategies used by small and large birds and determine whether small birds are more stable. This research will reveal how bipeds walk and run over uneven terrain without falls or injury. Mobility without falls and injury is particularly important for the wellbeing of ageing and gait impaired individuals. The findings are likely to have high impact in these areas, inspiring innovation in human fall prevention, gait rehabilitation, and the design of prosthetics, orthotics and other mobility assistance devices.