Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada.
Eur J Appl Physiol. 2013 Feb;113(2):437-47. doi: 10.1007/s00421-012-2448-z. Epub 2012 Jul 10.
Muscle-tendon gearing is the ratio of the muscle-tendon unit velocity to the fascicle velocity and can be expressed as the product of the gearing within the muscle belly and the gearing due to tendon stretch. Previous studies have shown that gearing is variable and increases at higher velocities. Changes in the muscle activation levels and force development have been suggested to affect tendon gearing and thus muscle-tendon unit gearing. However, the role of belly gearing as a part of muscle-tendon gearing and its associations with structural aspects of muscle and thus movement performance are important facets that need to be studied. The two gastrocnemii of twenty young adults were tested during isokinetic and isotonic contractions on an ankle dynamometer. Ultrasound images of both muscles were collected during contractions and were later digitised. Gearing was also predicted using a 2-dimensional panel model of these muscles. The results from experimental and models tests showed increases in gearing with greater torque levels at slower contraction velocities. However, in the isotonic models there was a substantial increase in gearing at faster contraction velocities. The level of muscle-tendon unit gearing is largely determined by the belly gearing, but its variability is driven by changes in tendon gearing that in turn is a factor of the muscle activation and coordination. The belly thickness of the medial gastrocnemius decreased during contractions, but increased for the lateral gastrocnemius. It is likely that changes to the belly shape and 3-dimensional structure are important to the gearing of the muscle.
肌肉肌腱传动比是肌肉-肌腱单元速度与肌束速度的比值，可以表示为肌腹中传动比和肌腱拉伸引起的传动比的乘积。先前的研究表明，传动比是可变的，并且在较高速度下增加。肌肉激活水平和力发展的变化被认为会影响肌腱传动比，从而影响肌肉-肌腱单元传动比。然而，作为肌肉-肌腱传动比一部分的肌腹中传动比及其与肌肉结构方面的关系，以及对运动表现的影响，是需要研究的重要方面。二十名年轻成年人的两条小腿三头肌在踝关节测力计上进行等速和等张收缩测试。在收缩过程中采集了两块肌肉的超声图像，并在之后对其进行了数字化处理。还使用这些肌肉的二维板模型来预测传动比。实验和模型测试的结果表明，随着较慢收缩速度下扭矩水平的增加，传动比也随之增加。然而，在等张模型中，在更快的收缩速度下，传动比会大幅增加。肌肉-肌腱单元传动比在很大程度上取决于肌腹中的传动比，但它的可变性是由肌腱传动比的变化驱动的，而肌腱传动比又是肌肉激活和协调的一个因素。在收缩过程中，内侧比目鱼肌的肌腹中厚度减小，但外侧比目鱼肌的肌腹中厚度增加。肌腹中形状和三维结构的变化很可能对传动比很重要。
