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Fig. 5. Power output of the dl1 muscles is plotted over a range of
activation phases, experimental lengths and strain amplitudes that encompass
both peak power and in vivo operating conditions. (A–C)
Variation in mechanical power output as a function of experimental length.
Experimental length is normalized to operating length. Each plot shows
measurements taken at one peak-to-peak strain amplitude normalized to
Lop: (A) 0.048, (B) 0.083, (C) 0.115. Within each plot,
each curve shows data from measurements at one of five values of the phase of
activation: 
0.31, 
0.37, 
0.42, 
0.47, •
0.52. At each amplitude power output was consistently lowest at the phase
values (0.47 and 0.52) that were closest to the phase of activation measured
in vivo (0.49±0.04; Tu and
Daniel 2004). (D–F) Contour plots showing power output,
coded by color, as a function of the phase of activation and experimental
length. Each plot is based on 90 measurements of power taken at five values of
activation phase and 18 values of experimental length. The contour lines were
fitted to the data by interpolation using an inverse distance method
(griddata.m, Matlab v.4, The Math Works Inc., Natick MA USA). Each plot shows
measurements taken at one peak-to-peak strain amplitude, normalized to
Lop: (D) 0.048, (E) 0.083, (F) 0.115. At all three
amplitudes, power output near the values of operating length and phase of
activation measured in vivo (open circle) was substantially lower
than the peak power output. The mean strain amplitude measured in
vivo (0.090±0.031Lop) lies between the
amplitudes tested in B,C, and E,F. Data in A–F are from one muscle
preparation (Moth 6 in Tables
1,
2).
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