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UBC Theses and Dissertations

Muscle function and control roles of the elbow flexion system in European Starlings Wood, Leo


The muscular basis for dynamically changing wing shape in birds is not well understood, owing to the complex and redundant network of muscles in the avian wing as well as a poorly- understood and diverse avian musculature. In passerines the biceps, Tensor Propatagialis Brevis (TPB), and Tensor Propatagialis Longus (TPL) share redundant control of elbow flexion. The TPB and TPL are smaller than the biceps but their lever arms are considerably larger, which suggests that the three muscles should produce similar elbow torque. Another distinct anatomical feature is that the TPL and TPB has have long in-series tendons unlike the biceps. Collectively, the anatomy of theses muscles suggests a hypothesis for the control of elbow flexion in flight: The distally attached TPL and TPB with long in-series tendons act primarily in torque control, whereas the proximally-attached biceps with no in-series tendon acts primarily for position control. To test this hypothesis, I collected EMG and high-speed kinematics on European starlings (Sturnus vulgaris) flying in a wind tunnel under varied conditions. A treatment was applied of attached weights to the distal wing on some flights to alter wing inertia and observe corresponding changes in kinematics and muscle activity suggesting specific muscle control roles. Wing weights did not have a robust effect on elbow kinematics or muscle activity, but EMG, kinematics, and morphology data suggested different functional roles for the three muscles. All three elbow flexors showed peak activity at the beginning of the downstroke, and the biceps demonstrated timing consistent with a role stabilizing the elbow. The TPB and TPL had in vivo timing and morphology consistent with unique roles for wing morphing, with precise and short-duration activity from the TPB consistent with its role in manus extension as well as elbow flexion and a two-pulse response of the TPL consistent with storage and release of elastic energy.

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