Fig. 1. In vivo zebra finch pectoralis fascicle strain and EMG activity. Traces show representative data obtained at a flight speed of 10 m s^–1. Fascicle segment length was measured in situ by sonomicrometry. Muscle activity was measured using a bipolar EMG electrode (see text). Fascicle length is shown relative to resting length L₀ measured with the bird resting on a perch.