Moore Alexis L, Budny Joseph E, Russell Anthony P, Butcher Michael T
Department of Biological Sciences, Youngstown State University, Youngstown, OH 44555, USA.
J Morphol. 2013 Jan;274(1):35-48. doi: 10.1002/jmor.20074. Epub 2012 Sep 15.
Evaluation of the relationships between muscle structure and digging function in fossorial species is limited. Badgers and other fossorial specialists are expected to have massive forelimb muscles with long fascicles capable of substantial shortening for high power and applying high out-force to the substrate. To explore this hypothesis, we quantified muscle architecture in the thoracic limb of the American badger (Taxidea taxus) and estimated the force, power, and joint torque of its intrinsic musculature in relation to the use of scratch-digging behavior. Architectural properties measured were muscle mass, belly length, fascicle length, pennation angle, and physiological cross-sectional area. Badgers possess hypertrophied shoulder flexors/humeral retractors, elbow extensors, and digital flexors. The triceps brachii is particularly massive and has long fascicles with little pennation, muscle architecture consistent with substantial shortening capability, and high power. A unique feature of badgers is that, in addition to elbow joint extension, two biarticular heads (long and medial) of the triceps are capable of applying high torques to the shoulder joint to facilitate retraction of the forelimb throughout the power stroke. The massive and complex digital flexors show relatively greater pennation and shorter fascicle lengths than the triceps brachii, as well as compartmentalization of muscle heads to accentuate both force production and range of shortening during flexion of the carpus and digits. Muscles of most functional groups exhibit some degree of specialization for high force production and are important for stabilizing the shoulder, elbow, and carpal joints against high limb forces generated during powerful digging motions. Overall, our findings support the hypothesis and indicate that forelimb muscle architecture is consistent with specializations for scratch-digging. Quantified muscle properties in the American badger serve as a comparator to evaluate the range of diversity in muscle structure and contractile function that exists in mammals specialized for fossorial habits.
对穴居物种肌肉结构与挖掘功能之间关系的评估有限。獾和其他穴居专家预计具有巨大的前肢肌肉，其肌束较长，能够大幅缩短以产生高功率，并向底物施加高向外力。为了探究这一假设，我们量化了美洲獾（Taxidea taxus）胸肢的肌肉结构，并估计了其固有肌肉组织在抓挠挖掘行为中的力、功率和关节扭矩。测量的结构特性包括肌肉质量、肌腹长度、肌束长度、羽状角和生理横截面积。獾拥有肥大的肩部屈肌/肱骨内收肌、肘部伸肌和指屈肌。肱三头肌特别发达，肌束长且羽状少，其肌肉结构具有大幅缩短能力和高功率。獾的一个独特特征是，除了伸展肘关节外，肱三头肌的两个双关节头（长头和内侧头）能够向肩关节施加高扭矩，以促进前肢在整个动力冲程中的内收。巨大而复杂的指屈肌比肱三头肌表现出相对更大的羽状和更短的肌束长度，并且肌头有分区，以在腕骨和手指屈曲时增强力的产生和缩短范围。大多数功能组的肌肉在产生高力方面表现出一定程度的特化，并且对于在强力挖掘动作中抵抗高肢体力量稳定肩关节、肘关节和腕关节很重要。总体而言，我们的研究结果支持这一假设，并表明前肢肌肉结构与抓挠挖掘特化一致。美洲獾中量化的肌肉特性可作为一个比较标准，以评估专门适应穴居习性的哺乳动物在肌肉结构和收缩功能方面的多样性范围。
