Quadrupedal mammals that differ greatly in size generally adopt distinct limb postures during locomotion. Small animals use a crouched posture with their limbs held more flexed while large animals use a more upright posture with their limbs held relatively straight. Despite our understanding of this scaling of limb configuration, we know little about how such postural differences influence the actions of homologous limb muscles in animals of varying size. Indeed, we have little appreciation for the in vivo behavior of quadrupedal mammalian limb muscles more generally; for no animal are actions of a hip, knee and ankle extensor well understood for any gait. The proposed work involves studying patterns of length change and activation in major hindlimb muscles of select mammalian species that differ widely in size. Two experimental approaches will be used to explore how body size and limb posture affect limb muscle function during locomotion. First, using sonomicrometry and electromyography, strain and activation patterns will be measured and compared among limb muscles of multiple rodent species ranging in size over three orders of magnitude (mice to capybara). Data will be used to test the general hypothesis that homologous muscles function differently in closely related animals that differ in size and limb posture. In the second approach, limb posture, muscle architecture and patterns of muscle strain and activation will be characterized in several mammal species over ontogeny. This approach will address whether changes in size that occur during growth influence limb muscles in a manner similar to size differences that have evolved among various mammalian species. Together, these distinct approaches will (1) provide critical insight into how muscles throughout the mammalian hindlimb operate in vivo during locomotion and (2) will help clarify the importance of animal size in shaping the actions of individual limb muscles both through ontogeny and across phylogeny. The proposed work will also have the broader impact of fostering research opportunities for talented young women interested in the biological sciences. The PI works at a single-gender institution and two students each year will collaborate on the projects, learning valuable research skills, presenting results from their work at national meetings, and co-authoring papers.
