CARROLL, Andrew M.*; WAINWRIGHT, Peter C.; COUGHLIN, David J.; Concord Field Station, Harvard University; University of California, Davis; Widener University: Muscle function and muscular power output during suction feeding

Muscle power output is thought to limit suction feeding performance, yet it has never been directly measured. In this study, epaxial activation and strain, hyoid depression, and intra-oral pressure were simultaneously measured in the largemouth bass (Micropterus salmoides) feeding on elusive prey. A mechanical model of muscle force transmission between the neurocranium and oral cavity was used to estimate muscle stress, work, and power based on buccal pressure and morphological measures. The epaxials shortened from rest an average of 9% of their length, with the highest efforts producing greater than 20% strain. Onset of shortening was simultaneous with or shortly after (<10 ms) onset of activation. Maximal net power for individual fish ranged from 17 to 137 W kg-1. Muscle power was significantly correlated with rectified EMG area (r=0.80; p<0.0001). The power required for cranial expansion was significantly correlated with epaxial power (r=0.81; p<0.0001), and the power exponent of this relationship (~1 for 3 of the 4 fish) implies that epaxial power accounts for most of the power of cranial expansion. The limitations imposed by the kinematic requirements and loading environment of suction feeding (short delay between activation and strain, maximal stress occurring after shortening, operation at lengths shorter than resting length) may reduce muscular power production. This study marks the first comprehensive simultaneous measurement of all aspects of muscle function (activation, strain, and force), the first direct measurement of muscular power, and the first direct measurement of the power cost of cranial expansion during suction feeding.