State Key Laboratory of Fluid Power and Mechatronic Systems, School of Mechanical Engineering, Zhejiang University, 310027 Hangzhou, China.
Department of Mechanical and Materials Engineering, Queen's University, Kingston, ON, Canada.
J Biomech. 2021 Mar 5;117:110264. doi: 10.1016/j.jbiomech.2021.110264. Epub 2021 Jan 20.
Springy poles are a unique load-carrying tool and inspire novel designs of other load-carrying systems. Previous experiments have shown that highly compliant poles with a natural frequency lower than step frequency are more economical than rigid poles during load carriage in walking and this was successfully explained in later modeling studies. However, an energetic benefit was not observed during running with highly compliant poles. We speculate that gait type (running versus walking) may be a factor accounting for the different observations. An optimization-based biped model is adopted to predict the energy cost of load carriage with poles during running, with the parameters from previous experimental studies. The predicted load motion and load-body interaction force agree well with experimental measurements. Compared to running with rigid poles, the highly compliant pole results in reduced peak ground reaction force, longer stance phase duration, and higher energy cost. The changes in running energetics are further found to depend on the natural frequency of the load-pole system relative to the step frequency, but with an opposite trend compared to the changes in walking energetics during pole carriage. Highly compliant poles cost more energy than rigid poles during running, while stiffer poles with a higher natural frequency may offer energetic benefits. This study indicates that the fundamental difference in gait type has a profound influence on the energetic performance of load-carrying devices and this should be taken into consideration in future device designs.
弹性杆是一种独特的承载工具，激发了其他承载系统的新颖设计。先前的实验表明，在步行过程中，具有低于步频的自然频率的高弹性杆比刚性杆更经济，这在后来的建模研究中得到了成功解释。然而，在使用高弹性杆跑步时，并没有观察到能量上的好处。我们推测，步态类型（跑步与步行）可能是导致不同观察结果的一个因素。采用基于优化的双足模型来预测跑步时使用杆进行负载搬运的能量成本，使用来自先前实验研究的参数。预测的负载运动和负载-身体相互作用力与实验测量值吻合良好。与使用刚性杆跑步相比，高弹性杆会导致峰值地面反作用力减小、支撑阶段持续时间延长和能量成本增加。进一步发现，跑步能量学的变化取决于负载-杆系统的自然频率与步频的相对关系，但与使用杆进行步行时的能量学变化趋势相反。在跑步时，高弹性杆比刚性杆消耗更多的能量，而具有更高自然频率的更刚性的杆可能具有能量优势。这项研究表明，步态类型的根本差异对承载设备的能量性能有深远影响，在未来的设备设计中应考虑这一点。
