Joint friction has never previously been considered in the computation of mechanical and metabolic energy balance of human and animal (loco)motion, which heretofore included just muscle work to move the body centre of mass (external work) and body segments with respect to it. This happened mainly because, having been previously measured ex vivo, friction was considered to be almost negligible. Present evidences of in vivo damping of limb oscillations, motion captured and processed by a suited mathematical model, show that: (a) the time course is exponential, suggesting a viscous friction operated by the all biological tissues involved; (b) during the swing phase, upper limbs report a friction close to one-sixth of the lower limbs; (c) when lower limbs are loaded, in an upside-down body posture allowing to investigate the hip joint subjected to compressive forces as during the stance phase, friction is much higher and load dependent; and (d) the friction of the four limbs during locomotion leads to an additional internal work that is a remarkable fraction of the mechanical external work. These unprecedented results redefine the partitioning of the energy balance of locomotion, the internal work components, muscle and transmission efficiency, and potentially readjust the mechanical paradigm of the different gaits.

中文翻译：

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人体运动中阻尼肢体振动的摩擦内功

在计算人类和动物（运动）运动的机械和代谢能量平衡时，以前从未考虑过关节摩擦，迄今为止，关节摩擦仅包括移动身体重心的肌肉工作（外部工作）和与其相关的身体部位。发生这种情况的主要原因是，之前已经在体外测量过，摩擦被认为几乎可以忽略不计。肢体振动的体内阻尼、由合适的数学模型捕获和处理的运动的现有证据表明：（a）时间过程是指数的，表明所有涉及的生物组织都存在粘性摩擦；(b) 在摆动阶段，上肢的摩擦力接近下肢的六分之一；(c) 下肢负重时，在倒立的身体姿势中，可以研究在站立阶段受到压缩力的髋关节，摩擦力要高得多并且取决于负载；(d) 运动过程中四肢的摩擦导致额外的内部功，这是机械外部功的显着部分。这些前所未有的结果重新定义了运动能量平衡的划分、内部工作成分、肌肉和传输效率，并可能重新调整不同步态的机械范式。