Neptune R R, Zajac F E, Kautz S A
Department of Mechanical Engineering, University of Texas at Austin, TX 78712, USA.
J Biomech. 2004 Jun;37(6):817-25. doi: 10.1016/j.jbiomech.2003.11.001.
Inverted pendulum models of walking predict that little muscle work is required for the exchange of body potential and kinetic energy in single-limb support. External power during walking (product of the measured ground reaction force and body center-of-mass (COM) velocity) is often analyzed to deduce net work output or mechanical energetic cost by muscles. Based on external power analyses and inverted pendulum theory, it has been suggested that a primary mechanical energetic cost may be associated with the mechanical work required to redirect the COM motion at the step-to-step transition. However, these models do not capture the multi-muscle, multi-segmental properties of walking, co-excitation of muscles to coordinate segmental energetic flow, and simultaneous production of positive and negative muscle work. In this study, a muscle-actuated forward dynamic simulation of walking was used to assess whether: (1). potential and kinetic energy of the body are exchanged with little muscle work; (2). external mechanical power can estimate the mechanical energetic cost for muscles; and (3.) the net work output and the mechanical energetic cost for muscles occurs mostly in double support. We found that the net work output by muscles cannot be estimated from external power and was the highest when the COM moved upward in early single-limb support even though kinetic and potential energy were exchanged, and muscle mechanical (and most likely metabolic) energetic cost is dominated not only by the need to redirect the COM in double support but also by the need to raise the COM in single support.
行走的倒立摆模型预测，在单腿支撑期，身体势能与动能的交换所需的肌肉功很少。行走过程中的外部功率（测量得到的地面反作用力与身体质心（COM）速度的乘积）常被用于分析，以推断肌肉的净功输出或机械能消耗。基于外部功率分析和倒立摆理论，有人提出，主要的机械能消耗可能与步间转换时重定向质心运动所需的机械功有关。然而，这些模型没有考虑行走的多肌肉、多节段特性，肌肉的共同兴奋以协调节段能量流，以及肌肉正功和负功的同时产生。在本研究中，采用肌肉驱动的行走正向动力学模拟来评估：（1）身体的势能和动能是否以很少的肌肉功进行交换；（2）外部机械功率是否可以估计肌肉的机械能消耗；以及（3）肌肉的净功输出和机械能消耗是否主要发生在双腿支撑期。我们发现，肌肉的净功输出无法从外部功率估计得出，并且当质心在单腿支撑早期向上移动时最高，尽管动能和势能发生了交换，并且肌肉的机械（很可能还有代谢）能量消耗不仅由双腿支撑期重定向质心的需求主导，还由单腿支撑期抬高质心的需求主导。
