The purpose of the study is to obtain performance measurements and participant feedback about use of an investigational prosthetic foot compared to the participant's usual prosthetic foot. To accomplish this, the study will use a combination of laboratory motion analysis, functional tests, and community mobility trials where participants complete questionnaires and interviews about use of an investigational prosthetic foot compared to the participant's usual prosthetic foot.

Individuals with amputations that participate in the (optional) motion analysis sub-study at the University of Washington will complete forward walking, side-step, and across river rock with usual foot (session 1), and also with the investigational foot locked and unlocked (session 2) after an accommodation period of between 1-4 weeks. The participants will rate their experiences using socket comfort score and the socket pressure score.

Control participants recruited at the University of Washington to provide information about performance for people without amputation will go through the consenting process, then will be asked to complete forward walking, Figure-of-8 Walk Test, Narrowing Beam Walking Test, side-step, and walking across river rock surface. These tests will be conducted at a single session.

If the participant with an amputation is eligible and wishes to participate, an appointment will be made for the person to come to the University of Washington Motion Analysis Lab or WillowWood, in Mt. Sterling, Ohio. The participant will meet with a researcher and clinical prosthetist to go through the consenting process. At that time, participants will complete the demographic data questionnaire.

The prosthetist will assess the condition and fit of the participant's current prosthesis for alignment, fit, and condition. The prosthetist will also inspect the participant's residual limb for skin condition. People presenting with significant skin breakdown will not be eligible to participate. The prosthetist will also determine how best to set up the current socket system with the investigational foot at that time.

Motion analysis trials of the investigational foot compared to the participant's usual foot. Participants will complete forward walking, side-step, and across river rock with usual foot (session 1), and also with the investigational foot locked and unlocked (session 2) after an accommodation period of between 1-4 weeks. The UW will conduct optically-based motion analysis using an 8-camera Qualisys motion capture system 4 embedded tri-axial ground reaction force platforms and a river rock-substrate surface that is parallel to the main motion capture space. For all motion analysis tests, retroreflective markers are taped to anatomical landmarks that are compatible with Visual 3-D kinematic modeling software. Motion data are captured at 120 Hz.

Motion Analysis Tests Forward walking. Participants will walk at a self-selected speed on a level surface for 10 m. In the center of the calibrated walking area, the participant will step on force plates. Marker position and reaction forces will be recorded for 2 sequential steps of the prosthetic side for participants with amputations, or matched side for control subjects. After a practice test, 3 tests where the prosthetic side successfully contacts the force plates will be recorded.

Side-step. Participants will perform the test in a similar manner to forward walking but will instead move laterally over the 10 m surface and across the centrally placed force plates. The order of side-stepping to the right or left will be randomly assigned. Participants will be asked not to cross-over their feet. After a practice test, 3 tests in each direction, where the prosthetic side or matched side successfully contacts the force plates, will be recorded.

Walking across river rock surface. Participants will walk in a direct path through the center of the river rock. They will be wearing a safety harness and will be attached to an overhead moving protection system. Participants will use the visual field limiting goggles during the river rock walking test. After practice tests, 3 tests will be recorded.

Modified socket comfort score and pressure score. Following each test protocol, participants will be asked to rate the socket comfort during the activity from 0 to 10 (with 0 being the least comfortable and 10 being the most comfortable imaginable) and pressures of the prosthetic socket on their residual limb during the activity from 0 to 10 (with zero being none and 10 being the highest imaginable). Participants will be asked to qualify the score with subjective comments.

Community Walking Trials (CWT) of the Investigational foot. To assess the benefit of the investigational foot, a combination of subjective and objective measures will be collected following 2- to 4-week periods of use. During the first laboratory visit, subjects will complete functional tasks with their existing prosthesis, as well as complete the Prosthetic Evaluation Questionnaire (PEQ) and the Comprehensive Lower Limb Amputee Socket Survey (CLASS). Next, they will be fit with the investigational foot and complete a 2- to 4-week at-home use period. A team member will contact the participant about one week after they start using the investigational foot to see how things are going and if there are any issues or problems to address (such as is the degree of stiffness appropriate) that may prompt a re-fitting. If this occurs, the 2- to 4-week at-home use period will re-start, increasing the participant's total amount of time in the study. During at-home use, participants will be prompted to complete a daily, structured, online logbook formatted in REDCap.

During the second visit, subjects will again complete the PEQ and CLASS, and repeat the same functional tasks as at the first visit but while wearing the investigational foot (locked and unlocked linkage). During this visit, a semi-structured interview will be conducted and recorded using Zoom. At the end of the visit, subjects will be re-fit with their original prosthetic foot and will complete another 2- to 4-week at-home use period with logbook entries before completing study questionnaires and a final interview.

Quantitative instruments - Community Walking Trials PEQ Subscales: The PEQ is a 9-scale instrument that has good psychometric properties and has been validated. The PEQ subscales vary from 0 (worst) to 100 (best). PEQ subscales of residual limb health, ambulation, utility, and sounds were selected for this study and comprise a total of 24 visual analogue scale questions.

CLASS: The intent of the CLASS is to provide greater insight into the cause of socket dissatisfaction compared to the Socket Comfort Score. To accomplish this, the CLASS includes 4 subcategories; 1) stability, 2) suspension, 3) comfort, and 4) appearance. Each subcategory contains 3-4 items scored using a 5-point scale that relate to common tasks such as standing, sitting, walking, and ascending and descending stairs.

Semi-structured interview: Participants' lived experiences using the investigational foot in comparison to the participant's usual foot will be collected using qualitative research methods. There will be an exit interview using open-ended questions to obtain qualitative data on foot performance and comparisons of foot prostheses. The interviews will be audio recorded. Interviews may be conducted remotely.

Daily Log Book: During home use of the participant's usual foot and the investigational foot, participants will keep an activity log (completed either electronically or on paper) that encourages descriptions of activities, including strengths and limitations of foot performance.

Functional Tasks Figure-of-8 Walk Test: Subjects will begin the task standing between the 2 cones. The subject will walk a figure-of-8 course 3 times for each condition at their self-selected pace and stop when they return to the start position. Time to complete the test and number of steps will be collected.

Narrowing Beam Walking Test:

The test consists of walking across a beam that has 4, 6-foot long sections, each one narrower than the previous one. The narrowing beam is 2" above the floor. When ready, the subject will begin walking along the beam while keeping their feet pointed in the direction of the beam (no side-stepping allowed). Subjects must keep their arms crossed in front of their body to eliminate the use of their arms to maintain balance. For this test of balance, the distance along the beam will be measured.

Inclusion Criteria:

• Unilateral below knee amputation, use a prosthetic foot for at least 1 year
• Ability to walk 400 meters on level ground without using a walking aid and without an increase in pain
• Ability to read, write, and comprehend English

Exclusion Criteria:

• Residual skin breakdown
• Weight over 300 lbs

4-8 weeks per individual participant