In individuals with transtibial amputation, the prosthetic limb plays a critical role in restoring walking abilities, and an important goal of prosthetic engineering is to replicate the natural ankle-foot system (NAFS). With the growing complexity of modern prostheses, examining the functions of lower extremity structures during gait has become increasingly difficult. Traditional biomechanical analyses do not fully quantify NAFS function and are not valid for the increasing number of prostheses that lack anatomically-congruent structures. Therefore, the overall goal of this dissertation was to develop and demonstrate a novel biomechanical method for characterizing the total mechanical power and energy profiles of anatomical and prosthetic below-knee structures during stance in gait.

This was accomplished by:​ 1) quantifying the total power of NAFS by combining previously developed techniques for estimating ankle joint and distal foot powers, 2) developing and validating a unified deformable (UD) segment power analysis method for quantifying the mechanics of anatomical and disparate prosthetic below-knee structures, and 3) applying the UD method in two case studies to compare the power and energy characteristics among anatomical and two distinct prosthetic below-knee systems.

The results indicated that the anatomical ankle joint and distal foot structures collectively perform net negative work during stance across a range of walking velocities. The UD method effectively quantified more than 95% of the total power of NAFS. Furthermore, the UD method revealed distinct power and energy properties across anatomical and prosthetic limbs. These included evidence of ‘over-powering’ from a motorized prosthetic ankle, decreased magnitude and delayed timing of energy return during late stance in a passive-dynamic prosthesis, and increased negative work done by a ‘shock-absorbing’ prosthesis during early stance. Altogether, these studies demonstrated the technical and clinical utilities of the UD segment power analysis, and may provide valuable insights for the future customization and optimization of prosthetic designs.