Fig. 8. Peak LG force versus peak MG force (A) and peak LG stress versus peak MG stress (B) during walking (black circles) and running (red triangles). The broken line represents the null hypothesis that both muscles share force and stress equally. Note that, while the MG generates more force relative to the LG, the LG consistently generates more stress. As speed increases, the LG exhibits a greater increase in force and stress compared with the MG. Also shown is LG force plotted against MG force (C) for a representative sequence of a bird running at 2 m s^–1 on an inclined treadmill. The arrows indicate the direction of the loop starting at the onset of force in the LG. Note that force generation is weighted towards the LG during the early stages of stance and then towards the MG during the later part of stance. This pattern is extremely consistent among and between animals.