Muscle architecture and out-force potential of the thoracic limb in the eastern mole (Scalopus aquaticus)

Abstract

Moles have modified thoracic limbs with hypertrophied pectoral girdle muscles that allow them to apply remarkably high lateral out-forces during the power stroke when burrowing. To further understand the high force capabilities of mole forelimbs, architectural properties of the thoracic limb muscles were quantified in the Eastern mole (Scalopus aquaticus). Architectural properties measured included muscle mass, moment arm, belly length, fascicle length, and pennation angle, and these were used to provide estimates of maximum isometric force, joint torque, and power. Measurements of muscle moment arms and limb lever lengths were additionally used to analyze the out-force contributions of the major pectoral girdle muscles. Most muscles have relatively long fascicles and little-to-no pennation. The humeral abductor/rotators as a functional group are massive and are capable of relatively high force, power, and joint torque. Of this group, the bipennate m. teres major is the most massive and has the capacity to produce the highest force and joint torque to abduct and axially rotate the humerus. In general, the distal limb muscles are relatively small, but have the capacity for high force and mechanical work by fascicle shortening. The muscle architectural properties of the elbow extensors (e.g., m. triceps brachii) and carpal flexors (e.g., m. palmaris longus) are consistent with the function of these muscles to augment lateral out-force application. The humeral abductor/rotators m. latissimus dorsi, m. teres major, m. pectoralis, and m. subscapularis are calculated to contribute 13.9 N to out-force during the power stroke, and this force is applied in a 'frontal' plane causing abduction of the humerus about the sternoclavicular joint. Moles have several specializations of their digging apparatus that greatly enhance the application of out-force, and these morphological features suggest convergence on limb form and burrowing function between New and Old World moles.

Forelimb muscle architecture and myosin isoform composition in the groundhog (Marmota monax)

“…Calculated and estimated functional properties are presented as single values consistent with our previous studies (see Moore et al, 2013;Rose et al, 2013). Mass of each muscle group was normalized to total forelimb muscle mass and presented as an architectural index (AI) of proximal-to-distal muscle mass distribution (Smith et al, 2006;Williams et al, 2008 (Moore et al, 2013;Rose et al, 2013) were calculated as additional AIs to assess muscle functional capacity.…”

“…Muscles were periodically moistened with phosphate buffered saline (PBS) to prevent desiccation during dissection and measurement. Muscle architecture was quantified following the procedures used in our previous studies (see Moore et al, 2013;Rose et al, 2013). Briefly, muscle moment arm (r m ) and muscle length in situ were measured using digital calipers (CD-8 CSX, Mitutoyo, Japan) with the limb joints placed in a neutral position (i.e.…”

Functional Morphology of the Forelimb of the Nine-Banded Armadillo (Dasypus novemcinctus): Comparative Perspectives on the Myology of Dasypodidae

“…Means ± SD (standard deviation) of muscle masses are also presented in Table 1. In addition, muscle architectural measurements (e.g., muscle belly length, fascicle length, and pennation angle) were taken using methods previously described in detail (Moore et al 2013;Rose et al 2013). These data, along with calculations of physiological crosssectional area (PCSA), maximum isometric force (F max ), joint torque, and muscle power are reported in Table 5.…”

“…In addition, available myology and morphological characters from other species of dasypodids will be evaluated to help remedy gaps in our knowledge of comparative muscle structure and digging function in armadillos. This work will also build on our previous studies of muscle architectural properties (Moore et al 2013;Rose et al 2013;Rupert et al 2015) to improve understanding of muscle traits that indicate specialization for fossorial habit as observed across diverse orders of mammals.…”

The private life of echidnas: using accelerometry and GPS to examine field biomechanics and assess the ecological impact of a widespread, semi-fossorial monotreme

“…Increased distal limb length and reduced bulk, favour longer, more rapid strides and faster running, but are at odds with the structural requirements for increased force generation needed for digging . For example, the forelimb structure of the fossorial eastern mole (Scalopus aquaticus) favours force generation to the detriment of rapid locomotion (Rose et al, 2013). Several other semi-fossorial Walking speeds were based on accelerometer data, calculated from peak frequency from walking epochs input into stride frequency-speed regression analysis (see Fig.…”