P1.44 Jan. 4 Effects of ontogenetic increases in size on muscle strain and activation patterns during goat locomotion BONVINI, Lauren*; GILLIS, Gary; Mount Holyoke College; Mount Holyoke College email@example.com
Size is known to have important consequences for the structural design and functional capacity of different physiological systems. The musculoskeletal system has been particularly well studied, and recent work has shown that homologous muscles in animals ranging from rats to horses can operate quite differently, undergoing distinct length-change patterns while active during the stride. At this point it is unclear whether size changes that occur intraspecifically, ie., growth over ontogeny, have any impact on limb structure or function during locomotion. The goal of this study was to test whether differences in size within a species alter aspects of limb posture and/or muscle actions in a manner parallel to that seen in interspecific scaling studies. Baby goats, Capra hircus, (4-6 kg) were trained to run over a range of speeds on a motorized treadmill. Animals were implanted with sonomicrometry crystals and electromyographic electrodes in the vastus lateralis and gluteobiceps, and strain and muscle activity patterns were recorded during locomotion. Both muscles are active over much of the stance phase but their length change patterns are distinct. The vastus lateralis undergoes a stretch-shorten cycle during stance in which fascicles initially lengthen approximately 6% of resting length (RL) before shortening 16 % of RL. Gluteobiceps fascicles generally shorten during stance, with total shortening amounts ranging from 25-30% RL during walking and trotting. For comparison, in adult goats (15-25 kg) total gluteobiceps shortening averages 32-33% RL during walking and trotting, while vastus stretching and shortening strains average 9% RL and 20-24% RL, respectively. Results suggest that actions in homologous muscles of baby and adult goats are qualitatively similar, but that strains may be slightly lower in the smaller animals.