Meeting Abstract
P3.143 Monday, Jan. 6 15:30 Estimating force outputs of cetacean axial locomotor muscles ARTHUR, L.*; MCLELLAN, W.; WOODWARD, B.; PISCITELLI, M.; WINN, J.; PABST, D.; UNC Wilmington; Univ. of Maine; Univ. of British Columbia; New River Kinematics LHA8694@uncw.edu
Cetaceans are streamlined swimmers that span a large range of body sizes [total length (TL) 1.5 – 25 m] and include species, such as the sperm and mysticete whales, with the largest locomotor muscles of any vertebrate. These marine vertebrates utilize their axial muscles to power swimming. To date, total body force output has only been measured in bottlenose dolphins swimming against a force plate (Williams et al. 1993, Goforth 1992), although thrust forces have been hydrodynamically modeled for a number of species. Our goal was to estimate epaxial muscle force output using directly measured morphological features of the musculoskeletal system, including muscle cross-sectional area (Am) and mass (Mm), for cetaceans ranging in size from bottlenose dolphins to blue whales. Maximal Am, directly measured from whole body cross-sections of a bottlenose dolphin, could be modeled as a half ellipse, with vertebral transverse and spinous processes forming its major axes. These maximal vertebral dimensions were measured for 89 specimens (21 species, TL 1.7 – 22.7 m). Force output based upon muscle area (FA) was calculated as Am x muscle stress (70 kPa) (Biewener 2005). Mm was also collected for 21 of these specimens (12 species, TL 1.8 – 9.7 m). Force output based upon muscle mass (FM) was calculated as Mm x 57 N/kg (Marden and Allen 2002). Both methods yielded scaling relationships less than those predicted for geometric similarity (F,AαTL1.6; FMαTL2.5). “Musculoskeletal fineness ratio” (defined here as TL/Am0.5) also increased with increasing body size; i.e. larger cetaceans possessed relatively smaller muscle dimensions. These results all suggest that length specific locomotor force output decreases with increasing body size in cetaceans.
