How are muscles constructed for high performance?

 


Limb Structure Images


                                                             

These studies originated in my lab with the first quantification of muscle architectural properties in the forelimbs of badgers. They involve measurement of muscle mass, belly length, fascicle length, pennation angles and moment arms. We are interested in understanding limb muscle specializations for digging behaviors (scratch-digging and humeral rotation) and how these properties evolved in different lineages. Badgers, and other scratch diggers, appear to have massive intrinsic muscle groups such as the shoulder stabilizers, elbow extensors and digital flexors. The muscle mass of the forelimbs is distributed further distal, which is different than the limb muscle organization in cursorial animals. Architectural properties of numerous muscles further indicate a functional capacity for high force production, power and joint torque. Collectively, these properties translate into high out-force applied to the substrate. Burrowing mammals, for example moles, have a different forelimb orientation and digging mechanics, and thus a different assemblage of muscle architectural properties. Major muscles that rotate the humerus (humeral abductors) contribute the high lateral out-force for tunneling, while distal muscle groups such as the elbow and carpal flexors, only supplement the high levels of out-force. We are just beginning to understand morphological and biomechanical diversity in fossorial forms.

Forelimb muscles and manus of the Eastern Mole. 

Photo: J.A. Rose

Lexi Moore completed the analysis in badgers for her Masters Thesis and we have published her work in the Journal of Morphology. We have also completed work on the forelimbs of both groundhogs and moles. Mole work was done in collaboration with Steve Huskey (Western Kentucky University). Quantification of muscle architecture (and fiber type) are now being evaluated in the forelimbs of armadillos (Dasypus novemcinctus) and chipmunks (Tamias striatus).

Scalopus aquaticus skeleton

posterior view 

Photos courtesy of Steve Huskey

Scalopus aquaticus skeleton   anterior view

Quantification of muscle architecture and MHC fiber type are also being evaluated in the hindlimbs of Eastern cotton-tail rabbits (Sylvilagus floridanus). This work is supported by NSF funding and is being done in collaboration with Jesse Young (NEOMED) and Gregory Smith (University of Akron).

Acceleration performance