S2-9 Thursday, Jan. 4 14:00 - 14:30 In vivo length changes in relation to intrinsic physiological properties in vertebrate skeletal muscles AHN, A.N.*; KONOW, N.; TIJS, C.; BIEWENER, A.A.; AHN-ROS, Anna; Harvey Mudd College; UMass Lowell; Harvard University; Harvard University firstname.lastname@example.org
Segments of vertebrate muscles contract heterogeneously under in vivo conditions and may also operate on different regions of their force-length relationships. To examine this idea, we measured adjacent central and distal segment strain patterns in vivo in the semimembranosus muscle of the American Toad (Bufo americanus) during hopping and in the sternohyoid muscle of the rat (Rattus rattus) during chewing, as well as in vivo strain patterns of the proximal and distal fascicles of the pennate medial gastrocnemius muscle of the rat during running. On the same day, we compared the in vivo lengths measured to their respective in vitro or in situ force-length properties. Within a fascicle, the adjacent central and distal segments of the frog semimembranosus and rat sternohyoid muscles shorten and lengthen heterogeneously in vivo. In vitro or in situ, the central muscle segments of both frog jumping and rat chewing muscles operated on the plateau region of their force-length relationships while the distal segments operated on the ascending limb of their force-length relationships. The ascending region provided stability for the sarcomeres in the distal segments. Two adjacent segments can operate on different regions of their force-length relationships simultaneously both in vivo and in vitro. By contrast, both proximal and distal fascicles of the rat medial gastrocnemius muscle operated on the ascending region of their force-length relationships with minimal in vivo strain differences between the fascicles, suggesting uniform fascicle strain behavior through the muscle. Understanding regional differences within muscles in vivo will allow us to link our understanding of sarcomere behavior with whole muscle behavior during movement.