AZIZI, E.; BRAINERD, E.L.; Univ. of Massachusetts,Amherst: Strain measurements of angled muscle fibers during swimming in an aquatic salamander Siren lacertina

Despite numerous studies that have focused on the mechanics and motor patterns of axial musculature in fishes, a functional understanding of myomere shape and axial muscle architecture has remained elusive. In contrast to the complex, three-dimensional shape of fish myomeres, the trunk myomeres of salamanders have a relatively simple morphology and can serve as a good system for exploring the mechanics of segmented muscle architecture. The lateral hypaxial muscles of the aquatic salamander Siren lacertina generally consist of three muscle layers with varying muscle fiber angles (some individuals have four layers). The varying fiber orientations in these muscle layers have allowed us to determine the effect of fiber angle on the magnitude of muscle fiber strain. We have used sonomicrometry to measure muscle fiber strain, shortening velocity and longitudinal segment strain in the lateral hypaxial muscle layers of Siren lacertina during steady swimming. We combine measurements of fiber angle and in vivo strain measurements with a video analysis in order to determine the relationship between muscle architecture, muscle dynamics and swimming kinematics. Our results indicate that muscle fiber strain is amplified when fiber orientation is at an angle relative to the longitudinal axis. This suggests that, relative to longitudinally oriented muscle fibers and for a given muscle fiber strain, angled muscle fibers will produce a greater amount of segment strain and body curvature. Supported by NSF IBN9875245 to ELB.