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Fig. 2. Gastrocnemius muscle performance in a human (A) and guinea fowl (B) during
running. Traces are scaled to align the stance periods of the running stride
(broken lines). EMG traces in A and B are rectified and averaged over many
stride cycles. (A) Average human gastrocnemius activity (EMG) relative to
ground reaction force (Dietz et al.,
1979), along with gastrocnemius fascicle length measured from
ultrasound recordings [traced from fig.
3 in Lichtwark and Wilson
(Lichtwark and Wilson, 2006)].
(B) Average guinea fowl gastrocnemus activity (EMG), muscle–tendon force
and fascicle length [thin lines indicate s.e.m.
(Daley, 2006)]. Note that the
muscle is activated with similar timing and undergoes a similar strain pattern
during stance in both the human and guinea fowl (as well as other animals).
The muscle is activated in anticipation of stance, with increases in activity
during stance suggestive of reflex feedback (e.g.
Dietz et al., 1979).
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