Meeting Abstract

98.1  Wednesday, Jan. 7  Muscle Function in a Complex Muscle During Terrestrial and Aquatic Locomotion CARR, J.A.*; MARSH, R.L.; Northeastern University; Northeastern University carr.je@gmail.com

Understanding the mechanical function of muscles with extensive origins and insertions is challenging. The Iliotibialis lateralis pars postacetabularis (ILPO) is one of the largest muscles in the hindlimb of cursorial birds, but this muscle has been reduced or lost in many orders of birds that locomote primarily via swimming. I hypothesized that the ILPO would not be actively contributing to the work done by the hindlimb during swimming. Common Moorhens (Gallinula chloropus) and Mallards (Anas platyrhynchus) were used to test this hypothesis. Common Moorhens and Mallards were used because these species have an ILPO and they employ both swimming and running to different degrees during routine locomotion in the wild. Using sonomicrometry and electromyography, we measured the strain and electrical activity in the ILPO during swimming and running at different speeds. Histological techniques, combined with sonomicrometry, were used to normalize the measured strain patterns to sarcomere length. Results show that in the both the Common Moorhen and the Mallard, during running, the ILPO shows a pattern of activity that is similar to the activity seen in the cursorial Guinea Fowl. However, during steady swimming, the ILPO shows reduced activity and experiences much smaller strains. These results are consistent with the hypothesis that the large ILPO in cursorial birds evolved in the context of selection for running ability, and its reduced size in swimming birds resulted from its lesser importance in propulsion during swimming. Supported by NIH AR47337 and NSF IOB-0542795 to RLM.