People with a lower extremity impairment can participate in high-impact activities such as running with the use of ankle-foot orthosis and running-specific prostheses (RSP). People having undergone limb salvage, use such devices as the IDEO passive-dynamic ankle-foot orthosis (PD-AFO), while people that have undergone transtibial amputation use RSPs to run and jump. Passive-dynamic AFOs includes a carbon-fiber strut, which attaches posteriorly to a custom-fabricated tibial cuff and foot plate. This device consists of different posterior strut stiffness categories which acts in parallel with the biological ankle joint to provide stability, while allowing elastic energy storage and return during the stance phase of running. However, the stiffness values of PD-AFOs struts have not been systematically determined, and these values can inform dynamic function and biomimetic PD-AFO prescription.

Accordingly, the first aim of my dissertation was to characterize the mechanical stiffness of the IDEO PD-AFO. To accomplish this goal, I constructed a custom bending apparatus and measured strut stiffness for 10° of anterior deflection and 5° of posterior deflection. I computed angular stiffness by measuring the applied moment and strut deflection. This study provided previously unpublished force-displacement profiles and stiffness values for each commercially available IDEO PD-AFO strut stiffness category. I found that the posterior carbon-fiber PD-AFO struts exhibited a linear force-displacement profile.

The second aim of my dissertation was to quantify the influence of prosthetic stiffness and mass on net metabolic power and biomechanical asymmetry and for females with transtibial amputations, and to measure how running speed interacts with RSP configuration. To accomplish this, I initially measured the effect of RSP stiffness and mass on net metabolic power at 2.5 m/s for females with transtibial amputation. I found that decreasing RSP stiffness by two stiffness categories from that recommended by the manufacturer decreased net metabolic power and improved stance-average vertical ground reaction force asymmetry in female with transtibial amputation. I found that adding 100 – 300 g of mass to the RSP had no significant effect on net metabolic power at 2.5 m/s in females with transtibial amputation. Next, I measured how RSP stiffness and mass affected biomechanical asymmetries across a range of running speeds, from 2.0 – 5.0 m/s, in females with transtibial amputation. I found that decreasing RSP stiffness improves biomechanical asymmetries and reduces the net metabolic power required to run at 2.5 m/s in females with transtibial amputation.

The third aim of my dissertation was to quantify the relationship between in-series stiffness of the long jump take-off step and jump distance in athletes with a without transtibial amputation. To accomplish this, I built a custom adjustable-stiffness springy platform and measured maximum run-up speed and jump distance for three different platform stiffnesses in non-amputee athletes. Next, I measured maximum-run up speed and jump distance for athletes with transtibial amputation, as they jumped with three different RSP stiffness categories. I found that decreasing in-series stiffness improves jump distance, regardless of run-up speed, in athletes with a without transtibial amputation.

Overall, my dissertation explores the effect of leg stiffness on running and jumping in athletes with lower limb impairment.