Fig. 4. A representative force-strain curve for a single pair of particles (middle aponeurosis; L_o). Each point (x) is from a maximal tetanic contraction via a different combination of ventral root filament bundles. At the lowest recruitment levels used in this study (15-20% of P_o), the strains were typically more than 50% of the strains attained at P_o. This implies the existence of a highly compliant toe region. The straight line is a tangent to the force-strain curve at 75% of P_o, and its slope is the stiffness of the tissue at that point. P_o for this muscle was 1.58 N. Thus, it can be seen from the relationship between this tangent line and the force-strain curve that the stiffness of the tissue did not vary much above 30% of P_o (0.5 N for this muscle).