Muscle architecture dynamics modulate performance of the superficial anterior temporalis muscle during chewing in capuchins

Myra F Laird,Andrea B Taylor,Callum F Ross,Michael C Granatosky

doi:10.1038/s41598-020-63376-y

Abstract

Jaw-muscle architecture is a key determinant of jaw movements and bite force. While static length-force and force-velocity relationships are well documented in mammals, architecture dynamics of the chewing muscles and their impact on muscle performance are largely unknown. We provide novel data on how fiber architecture of the superficial anterior temporalis (SAT) varies dynamically during naturalistic feeding in tufted capuchins (Sapajus apella). We collected data on architecture dynamics (changes in muscle shape or the architectural gear ratio) during the gape cycle while subjects fed on foods of different mechanical properties. Architecture of the SAT varied with phases of the gape cycle, but gape distance accounted for the majority of dynamic changes in architecture. In addition, lower gear ratios (low muscle velocity relative to fascicle velocity) were observed when animals chewed on more mechanically resistant foods. At lower gear ratios, fibers rotated less during shortening resulting in smaller pinnation angles, a configuration that favors increased force production. Our results suggest that architectural dynamics may influence jaw-muscle performance by enabling the production of higher bite forces during the occlusal phase of the gape cycle and while processing mechanically challenging foods.

Highlights

Jaw-muscle architecture is a key determinant of jaw movements and bite force
Coronal and sagittal fascicle angles were largest at minimum gape and smallest at maximum gape (Fig. 3C,D) and sagittal fascicle angles exhibited at least twice as much variation compared to coronal fascicle angles across the gape cycle
These results suggest that muscle gearing may play an important role in modulating muscle performance at submaximal activation during naturalistic behaviors

Summary

Introduction

Jaw-muscle architecture is a key determinant of jaw movements and bite force. While static lengthforce and force-velocity relationships are well documented in mammals, architecture dynamics of the chewing muscles and their impact on muscle performance are largely unknown. In combination with the geometry of the feeding system (i.e., height of the jaw joint above the tooth row and bite location along the tooth row)[5,6] these fundamental constraints impose trade-offs between bite force, jaw gape (vertical displacement of the lower jaw), and bite point (bite location along the toothrow) that must be confronted by natural selection While these static aspects of mammal feeding-system design are well studied with respect to bite force and jaw movement, e.g. refs. Tufted capuchins have features that facilitate the production of large muscle and bite forces without compromising gape; increased jaw-elevator PCSAs through added muscle mass rather than shorter fiber lengths and larger pinnation angles[12]. Muscle architecture can be defined as the internal arrangement of fibers relative to the force-generating axis of a muscle, e.g. ref

Methods

Results

Conclusion