Figure 1.

Functional diversification within and between hind limb muscles. (a) Diagrammatic representation of a guinea fowl showing the region of the limb that was the focus of study. (b) The location of the sonomicrometry crystals implanted into the MG (blue) and LG (red), and the orientation of the muscles relative to the centre of rotation of the knee (black dots). (c) Representative in vivo work loops for the LG, pMG and dMG. (i) An anticlockwise loop represents net positive work (e.g. LG) and (ii,iii) a clockwise loop (indicated by arrows) represents net negative work (e.g. pMG and dMG). (d) Two consecutive representative strides at 2 m s⁻¹ show the changes in fascicle length. The corresponding EMG signals are also shown in black with a scale bar, 2 mV (same for (i–iii)). The shaded regions indicate the stance phase of the stride. (e) Muscle stress corresponding with the strides in (d) for the LG (red) and MG (blue). (f) Mean frequency of the EMG versus standardized time (per cent of stride) for all three muscle locations (for sake of clarity, footfall occurs at approx. 40% of the stride). The warmer colours (red and orange) indicate the greatest intensity.