Higham Timothy E, Nelson Frank E
Department of Organismic and Evolutionary Biology, Harvard University, Concord Field Station, 100 Old Causeway Road, Bedford, MA 01730, USA.
Zoology (Jena). 2008;111(6):483-93. doi: 10.1016/j.zool.2008.01.001. Epub 2008 Jul 26.
Animals commonly move over a range of speeds, and encounter considerable variation in habitat structure, such as inclines. Hindlimb kinematics and muscle function in diverse groups of vertebrates are affected by these changes in behavior and habitat structure, providing a fruitful source of variation for studying the integration of kinematics and muscle function. While it has been observed in a variety of vertebrates that muscle length change can be minimal during locomotion, it is unclear how, and to what degree, in vivo muscle length change patterns are integrated with kinematics. We tested the hypothesis that the length of the turkey lateral gastrocnemius (LG), a biarticular muscle that has moments at the ankle and knee, is not solely affected by changes in joint kinematics. We recorded in vivo muscle length changes (using sonomicrometry) and hindlimb movements (using high-speed video) of wild turkeys running on various inclines, and at different speeds. We quantified the relationship between joint angle (knee and ankle separately) and muscle length in freshly euthanized specimens, and then applied an empirically derived correction for changes in pennation angle and tendon strain during locomotion to improve the accuracy of our predicted lengths. We estimated muscle length at four points during each stride and then compared these values with those measured directly. Other than during swing, the predicted changes in muscle length calculated from the changes in joint kinematics did not correspond with our measured values of LG length. Therefore, the lengths at which the LG operates in turkeys are not determined entirely by kinematics. In addition to strain in series elastic components, we hypothesize that heterogeneous strain within muscles, interactions between muscles and muscle pennation angle all contribute to the nonlinear relationship between muscle length changes and kinematics.
动物通常会在一定范围内改变速度，并在诸如斜坡等栖息地结构中遇到相当大的变化。不同类群的脊椎动物的后肢运动学和肌肉功能会受到这些行为和栖息地结构变化的影响，为研究运动学和肌肉功能的整合提供了丰富的变异来源。虽然在多种脊椎动物中都观察到，在运动过程中肌肉长度变化可能很小，但尚不清楚体内肌肉长度变化模式如何以及在何种程度上与运动学相结合。我们测试了这样一个假设：火鸡外侧腓肠肌（LG）是一块在踝关节和膝关节处都产生力矩的双关节肌肉，其长度不仅受关节运动学变化的影响。我们记录了野生火鸡在不同斜坡上以不同速度奔跑时的体内肌肉长度变化（使用超声测量法）和后肢运动（使用高速视频）。我们对刚处死后的标本中关节角度（分别为膝关节和踝关节）与肌肉长度之间的关系进行了量化，然后对运动过程中羽状角和肌腱应变的变化应用了根据经验得出的校正，以提高我们预测长度的准确性。我们在每个步幅的四个点估计肌肉长度，然后将这些值与直接测量的值进行比较。除了摆动期间，根据关节运动学变化计算出的肌肉长度预测变化与我们测量的LG长度值不相符。因此，火鸡中LG发挥作用的长度并非完全由运动学决定。除了串联弹性成分中的应变外，我们假设肌肉内的异质应变、肌肉之间的相互作用以及肌肉羽状角都导致了肌肉长度变化与运动学之间的非线性关系。
