Fig. 7. (A) Example of a stress versus strain relationship for the series elastic component of a red fibre bundle. The points show observations from recordings such as those shown in Fig. 5. Stress is that produced at the end of the step change in length, and strain is the size of the step change in length. The fitted line was calculated as described in the text. Strain, Y, is the sum of a constant, k, a linear component, a(x), and a saturating component, b(x), where x is stress. Y=k+a(x)+b(x), where a(x)=mx; if x<c, then b(x)=nx; if xc, then b(x)=nc. The fitted values were k=-0.0498, m=0.0381, n=0.0625 and c=0.186. The total strain (black line) is the sum of k (broken line) and a(x) (red line) and b(x) (green line). (B) Corresponding strain versus stress relationship with points and black line as in A. L, length change; L₀, fibre length at which maximum isometric force was produced; P₀, isometric force before shortening.