Ellis Richard G, Rankin Jeffery W, Hutchinson John R
Structure & Motion Laboratory, Department of Comparative Biomedical Sciences, The Royal Veterinary College, North Mymms, United Kingdom.
Pathokinesiology Laboratory, Rancho Los Amigos National Rehabilitation Center, Downey, CA, United States.
Front Bioeng Biotechnol. 2018 Nov 16;6:162. doi: 10.3389/fbioe.2018.00162. eCollection 2018.
Standing up from a prone position is a critical daily activity for animals: failing to do so effectively may cause an injurious fall or increase predation susceptibility. This sit-to-stand behaviour (StS) is biomechanically interesting because it necessitates transitioning through near-maximal joint motion ranges from a crouched (i.e., poor mechanical advantage) to a more upright posture. Such large joint excursions should require large length changes of muscle-tendon units. Here we integrate experimental and musculoskeletal simulation methods to quantify the joint motions, limb forces, and muscle fibre forces, activations and length changes during StS in an extreme athlete-the greyhound-which has large hindlimb muscles bearing short-fibred distal muscles and long tendons. Study results indicate that hindlimb anti-gravity muscle fibres operate near their ~50% limits of length change during StS; mostly by starting at highly lengthened positions. StS also requires high muscle activations (>50%), in part due to non-sagittal motions. Finally, StS movements require passive non-muscular support in the distal hindlimb where short-fibred muscles are incapable of sustaining StS themselves. Non-locomotor behaviours like StS likely impose important trade-offs between muscle fibre force capacity and length changes, as well as active and passive mechanisms of support, that have been neglected in locomotor biomechanics studies.
若无法有效完成此动作，可能会导致受伤摔倒或增加被捕食的易感性。这种从坐立到站立的行为（StS）在生物力学上很有趣，因为它需要通过近乎最大的关节运动范围，从蹲伏姿势（即机械优势较差）过渡到更直立的姿势。如此大的关节活动范围应该需要肌肉 - 肌腱单元有较大的长度变化。在这里，我们整合了实验和肌肉骨骼模拟方法，以量化一种极端运动员——灵缇犬在StS过程中的关节运动、肢体力量以及肌肉纤维力量、激活情况和长度变化。灵缇犬后肢肌肉发达，其远端肌肉纤维短且肌腱长。研究结果表明，后肢抗重力肌肉纤维在StS过程中接近其长度变化的约50%极限运作；主要是从高度拉长的位置开始。StS还需要较高的肌肉激活水平（>50%），部分原因是存在非矢状面运动。最后，StS动作需要后肢远端的被动非肌肉支撑，因为短纤维肌肉自身无法维持StS。像StS这样的非运动行为可能在肌肉纤维力量能力与长度变化之间，以及主动和被动支撑机制之间带来重要的权衡，而这些在运动生物力学研究中一直被忽视。
