Fig. 1. (A) A depiction of the pectoralis muscle, its attachment to the humerus at the deltopectoral crest (DPC) of the humerus, and implanted transducers. A pair of sonomicrometry crystals was implanted in the proximal portion of the pectoralis, and an EMG electrode was placed between the two crystals. A metal-foil strain gauge was attached to the dorsal surface of the DPC of the humerus. Wires from all these transducers were passed subcutaneously to a customized miniature plug attached to the bird's back. (B) Sonomicrometry and electromyogram (EMG) recordings are shown for three successive wingbeats at 7 m s^-1. The time course of pectoralis shortening (downstroke) is shaded in gray. (C) Pectoralis force recorded by the strain gauge and (D) z-axis (vertical) motion of the wrist and wing-tip obtained from a 3-D reconstruction of digitized markers based on 125 Hz dorsal and lateral camera views.