Fig. 5.

Sensitivity of the FR model in a aging—solid lines represent mature group, dashed lines represent aging, and dotted lines represents aged, b mature group healing, c aging group healing, and d aged group healing. In (b)–(d), solid lines represent uninjured, dashed lines represents 3 weeks post-injury, and dotted lines represents 6 weeks post-injury. The influence of the toe region modulus (blue) decreased with stretch as the tendon approached the estimated transition stretch. A switch in the influence of the moduli parameters is observable at the estimated transition stretch. The linear region moduli (red) became influential beyond the estimated transition stretch, though not reaching the same level of influence as that of the toe region modulus before the estimated transition stretch. A decrease in the influence of crimp (i.e., increase in the influence of $\mathit{\beta }$) is noticeable as the estimated stretch is approached. A delay in the estimated transition stretch due to injury is mostly observable in the mature group (b) and in the aged group (d)