Metatarsophalangeal Joint Dynamic Stiffness During Toe Rocker Changes With Walking Speed.

Dynamic joint stiffness (or simply "stiffness") is a customization criteria used to tune mechanical properties of orthotic and prosthetic devices. This study examines metatarsophalangeal (MTP) joint stiffness during the toe-rocker phase of barefoot walking and establishes baseline characteristics of MTP joint stiffness. Ten healthy individuals walked at 4 speeds (0.4, 0.6, 0.8, and 1.0 statures·s-1) over level ground. MTP sagittal plane joint angles and moments were calculated during the toe-rocker phase of stance. Least-squares linear regressions were conducted on the MTP moment versus angle curve to determine joint stiffness during early toe rocker and late toe rocker. Multilevel linear models were used to test for statistically significant differences between conditions. Early toe rocker stiffness was positive, while late toe rocker was negative. Both early toe rocker and late toe rocker stiffness increased in magnitude significantly with speed. This study establishes baseline characteristics of MTP joint stiffness in healthy walking, which previously had not been examined through a range of controlled walking speeds. This information can be used in the future as design criteria for orthotic and prosthetic ankle and ankle-foot devices that can imitate, support, and facilitate natural human foot motion during walking better than existing devices.