Lichtwark G A, Wilson A M
Structure and Motion Laboratory, Institute of Orthopaedics and Musculoskeletal Sciences, University College London, Royal National Orthopedic Hospital, Brockley Hill, Stanmore, Middlesex, HA7 4LP, UK.
J Exp Biol. 2005 Aug;208(Pt 15):2845-53. doi: 10.1242/jeb.01710.
The activation of a muscle depends on the function that it is performing and on the architectural properties of that muscle; the two are inextricably linked. Activation conditions such as activation timing, duration and amplitude can be varied throughout a cyclical movement (such as locomotion) and the length change of the whole muscle tendon unit (MTU) can also be varied. Architecturally, muscles have a range of fibre lengths, maximum force-producing capabilities and stiffness of the series elastic element (SEE). In the present work we use a model to explore the relationship between power output and efficiency of a muscle across a range of contraction conditions. We have also examined the mechanical and energetic effects of changing muscle architecture within the model. Our results indicate that whilst there are clear optimal conditions for achieving maximum power output and maximum efficiency, the design of the muscle allows high levels of both to be achieved over a range of activation conditions. This range changes with both SEE compliance and the amplitude of the cyclical length change. The results suggest that a compliant SEE allows a muscle to function closer to the maximum of both power output and efficiency. In addition, by varying the amplitude of the activation level, the efficiency can theoretically remain unchanged, whilst the power output can be modulated.
肌肉的激活取决于其执行的功能以及该肌肉的结构特性；二者紧密相连。激活条件，如激活时间、持续时间和幅度，在周期性运动（如 locomotion）过程中可以变化，并且整个肌肉肌腱单元（MTU）的长度变化也可以不同。在结构上，肌肉具有一系列的纤维长度、最大力量产生能力以及串联弹性元件（SEE）的刚度。在本研究中，我们使用一个模型来探索在一系列收缩条件下肌肉的功率输出与效率之间的关系。我们还在模型中研究了改变肌肉结构的力学和能量学效应。我们的结果表明，虽然存在实现最大功率输出和最大效率的明确最佳条件，但肌肉的设计使得在一系列激活条件下都能实现高水平的功率输出和效率。这个范围会随着 SEE 的顺应性和周期性长度变化的幅度而改变。结果表明，顺应性的 SEE 能使肌肉在更接近功率输出和效率最大值的状态下发挥功能。此外，通过改变激活水平的幅度，理论上效率可以保持不变，而功率输出可以得到调节。
