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Fig. 1. In vivo measurements of mechanical work and power output from the
pectoralis, the primary downstroke muscle of the avian wing are accomplished
using surgically implanted strain gauges calibrated to measure force from bone
strain on the deltopectoral crest of the humerus and using sonimicrometry
crystals to measure muscle length (A). Similar methods are employed for the
primary upstroke muscle, the supracoracoideus (not shown), which is located
deep to the pectoralis (Tobalske and Biewener, in press). (From
Hedrick et al., 2003.) (B) A
`work loop', the area of which represents in vivo mechanical work in
the pectoralis of a cockatiel Nymphicus hollandicus during one
wingbeat (adapted from Tobalske et al.,
2003). Arrows indicate the progression of contractile behavior.
Electromyography (EMG) activity in the pectoralis indicates that the muscle
functions to decelerate the wing at the end of upstroke and accelerate the
wing during the first third of downstroke.
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