Fig. 5. Peak muscle (circles) and tendon (triangles) stresses plotted against the ratio of muscle to tendon area (A_m/A_t), based on measurements obtained from direct in vivo muscle-tendon force recordings (solid) and those calculated from ground reaction forces and/or kinematics using inverse dynamics (open). Note that the variation in tendon stress (>20-fold) greatly exceeds that of muscle stress (fourfold), which may be hidden by graphing both sets of data on the same graph. Least-squares regressions are shown for both sets of data. See Table 1 for values and sources. In contrast to peak muscle stresses (R²=0.069, P>0.05), peak tendon stresses show a significant correlation with A_m/A_t (R²=0.753, P<0.01).