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Journal of Experimental Biology 162,131-155 (1992)
Published by Company of Biologists 1992

Stiffness and Damping Forces in the Intervertebral Joints of Blue Marlin (Makaira Nigricans)

JOHN H. LONG JR ¹

¹ Department of Zoology, Duke University, Durham, NC 27706, USA and Pacific Ocean Research Foundation, 74-425 Kealakehe Pkwy 15, Kailua-Kona, HI 96740, USA; Department of Biology, Vassar College, Poughkeepsie, NT 12601, USA

The stiffness and damping moments that are transmitted by intervertebral joints during sinusoidal bending were determined in the blue marlin, Makaira nigricans Lacépède. Using a dynamic bending machine, the angular stiffness (N m rad^-1) and damping coefficient (kg m² rad^-2 s^-1) of the intervertebral joints were measured over a range of bending frequencies, amplitudes and positions along the backbone. Angular stiffness increases with increasing bending amplitude, but, for some joints, the rate at which it changes with increasing bending frequency is negative. The precaudal intervertebral joints are less stiff than the caudal joints. The damping coefficient, which also shows regional variation, does not change with amplitude but does decrease with increasing bending frequency in joint positions three and five. Stiffness moments along the vertebral column, given the same amount of bending at each joint, are always greater than the damping moments. However, damping moments increase by an order of magnitude with an increase in bending frequency from 0.5 to 5.0Hz. The stiffness and damping moments determine the work that an external moment, such as muscle, must do over a complete cycle of bending. The external moments and work needed to bend an intervertebral joint are determined largely by the stiffness moments of the intervertebral joints.

Key words: intervertebral joints, Makaira nigricans, force transmission, stiffness, damping, blue marlin, dynamic bending

Accepted on September 9, 1991

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