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Fig. 1. (A) Recording sites within the pigeon pectoralis, showing the locations of
the sonomicrometry (SONO) crystals used to record in-series fascicle strain in
the anterior (Ant) and middle (Mid) regions of the sternobrachialis (SB)
portion of the pectoralis, together with SONO measurements obtained in the
posterior (Post) SB and thoracobrachial (TB) portion of the pectoralis to
assess regional patterns of fascicle strain. Electromyography (EMG) electrodes
were implanted immediately adjacent to the SONO crystal pairs. The middle SONO
crystal at the Ant and the Mid sites was used to `ping' the two opposing
receiving crystals to obtain adjacent in-series measurements of fascicle
segment strain at these two locations. Additionally, in three birds
measurements of aponeurosis (APO) strain were obtained to examine
series-elastic stretch of the aponeurosis resulting from forces transmitted to
the deltopectoral crest (DPC) from the TB and more posterior regions of the
SB. Measurements of overall muscle force were obtained from a strain gauge
attached to the dorsal aspect of the DPC, the ventral surface to which the
pectoralis has a tendinous insertion. See text for further details. (B) Map of
the pectoralis muscle based on digital images obtained from the muscles of the
six birds, showing the fascicle architecture and average recording locations
(magenta fascicles) for each muscle region. Measurements of fascicle length
and pinnation angle relative to the aponeurosis (shown in red) were determined
from the images and referenced to a coordinate system at eight defined points
along the SB and six points along the TB. To compare across animals, the
positions of the recording sites were normalized as a percentage of SB and TB
length relative to the caudal tip of the muscle. The locations (mean ±
S.D.) of the fascicle recordings sites is shown below.
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