24.3 Wednesday, Jan. 4 Mechanics and kinematics of the vertebral column in striped bass, Morone saxatilis NOWROOZI, Bryan N*; BRAINERD, Elizabeth L; Brown University; Brown University email@example.com
Variation in body stiffness impacts propulsive wave propagation and thrust generation during axial undulatory locomotion in fishes. The connective tissues of the vertebral column have been implicated in the regionalization of body stiffness and elastic recoil during locomotion. However, it is unclear which aspects of vertebral morphology are important to body stiffness, and to what extent vertebral stiffness impacts locomotion. The present study investigates the variation in angular stiffness and kinematics of intervertebral joints (IVJs) along the length of the striped bass, Morone saxatilis. We performed cyclic dynamic testing on IVJs postmortem at three frequencies (2, 5, and 7 Hz). Testing of IVJs from the cervical (joint 3), abdominal (joint 9), and caudal (joint 20) regions of five fish revealed lower angular stiffness in the caudal and cervical regions relative to the abdominal region. In addition, a substantial neutral zone of bending, where the IVJs bend freely without resistance, begins at 0° and ranges up to 12° in the cervical region, 10° in the abdominal region, and 15° in the caudal region. Hysteresis was fairly high (30-40%) in all regions. Additionally, high-speed fluoroscopy revealed that the maximum angles of IVJ bending attained in vivo lie within the neutral zone of bending. Using these kinematic and mechanical data, we estimate the magnitude of energy returned to the system by each cervical, abdominal, and caudal IVJ to be 9.0 x 10-5 J, 3.5 x 10-4 J, and 1.9 x 10-4 J, respectively. Taking into account the 24 IVJs present in a single fish, these elastic recoil estimates sum to just 1.2% of the 17.5 W of muscle power required during burst swimming. Thus, it is unlikely that the vertebral column of the striped bass provides substantial contributions to whole body stiffness and elastic recoil in vivo.