People with unilateral transtibial amputation typically use passive-elastic and running-specific prostheses to walk and run, respectively. Passive-elastic and running-specific prostheses cannot fully replicate the function of the biological ankle and foot, and people with unilateral transtibial amputation walk and run with biomechanical asymmetry between their affected (leg with the prosthesis) and unaffected (biological leg) legs. The biomechanical asymmetry between the affected and unaffected leg when walking and running may contribute to the increased prevalence of joint pain and osteoarthritis for people with unilateral transtibial amputation. Therefore, understanding how different prosthetic mechanical properties, designs, and configurations affect the biomechanics of walking and running can inform prosthetic prescription and design in order to potentially reduce the prevalence of joint pain and osteoarthritis for people with unilateral transtibial amputation.

In Chapter 1, I examine the walking and running biomechanics of non-amputees and compare them to the walking and running biomechanics of people with unilateral transtibial amputation in order to motivate prosthetic prescription and future prosthetic designs. In general, people with unilateral transtibial amputation walk and run with biomechanical asymmetry when using passive-elastic and running-specific prostheses that cannot fully replicate the function of a biological ankle and foot.

In Chapter 2, my co-authors and I present a manuscript that is under review at PLOS One where we characterize the axial stiffness, torsional stiffness, and hysteresis of low-profile passive-elastic prosthetic feet for a range of stiffness categories, sizes, and with and without a shoe. Characterizing the mechanical properties of prosthetic feet with and without shoes allows for objective comparisons between different prosthetic feet, categories, and sizes in order to better inform prosthetic prescription.

In Chapter 3, my co-authors and I present work from three manuscripts where we examine the effects of prosthetic stiffness categories and stance-phase power settings of a powered ankle-foot prosthesis (BiOM) on the biomechanics of walking at different speeds. We found that use of a prosthesis one category stiffer (+1) than recommended did not affect positive work done by the affected trailing leg during the step-to-step transition but reduced the magnitude of negative work done by the unaffected leading leg, possibly due to greater effective foot length ratio of the +1 category prosthesis. Prosthetic stiffness category had little to no effect on biomechanical asymmetry and joint kinetics. Moreover, we found that increasing the power setting of the BiOM increased the positive trailing leg work done by the affected leg during the step-to-step transition, but only reduced the magnitude of negative leading leg work done by the unaffected leg when walking at slow to moderate speeds. We found that use of the BiOM decreased contact time asymmetry compared to use of a passive elastic prosthesis at all walking speeds;​ however, use of the BiOM increased peak ground reaction force asymmetry when walking at slow (0.75 m/s) and fast (1.75 m/s) speeds. Finally, we found that increasing the power setting of the BiOM can increase the positive work done by the prosthesis during a stride and reduce the positive work done by the muscles surrounding the hip joints of both legs when walking 1.25-1.75 m/s. Our results suggest that people with unilateral transtibial amputation may benefit from using the BiOM tuned to power settings up to 20% greater than typically recommended.

Finally, in Chapter 4, my co-authors and I present a manuscript that was published in the Royal Society Open Science journal where we examine how different configurations of running-specific prosthetic model, stiffness, and height affect the biomechanics and asymmetry of people with unilateral transtibial amputation running at a range of speeds to improve the prescription and design of running-specific prostheses. Based on our results, prosthetists should prescribe a Jshaped running-specific prosthesis model with a shorter than recommended height to reduce stance average vertical ground reaction force asymmetry and potentially reduce injury risk for athletes with unilateral transtibial amputation. Moreover, a running-specific prosthesis that increases stiffness with running speed could minimize step frequency asymmetry across speeds;​ however, there is a potential trade-off between decreasing step frequency asymmetry and increasing contact length asymmetry. Ultimately, the work in this thesis provides insight into the design and prescription of lower-limb prostheses by furthering our understanding of the mechanical properties of passive-elastic prostheses and the effects of different prosthetic mechanical properties, designs, and configurations on the walking and running biomechanics of people with unilateral transtibial amputation.