In summary, subjects will be asked to wear a number of sensors and use different ankle-foot prostheses in place of their customary prosthesis. Data will be collected from the wearable sensors, VICON motion capture system, video cameras, and force sensors in the ground as they walk on level-ground, on a treadmill, and on stairs. The controller of any powered prosthesis will be electronically adjusted between trials or while the subject walks to determine how their gait changes in response to these changes. Trials will also be conducted with a standard passive prosthesis that would be prescribed for a person of similar height and weight.

Subject Selection and Consent:

Subjects will be selected based on the following priority. Subjects who have previously participated in similar studies with the Biomechatronics lab and who have already been screened for health and mobility level will be contacted first. If additional subjects are needed, a recruitment flyer and screening questionnaire will be sent to potential candidates. Copies of both the flyer and questionnaire are included in the attachments section. Prior to the experimental sessions, subjects will be asked to read and sign a informed consent form and will explain the project to them and answer any questions that they may have. They will also be given time to become familiar with the equipment being used before beginning any trials. If needed, subjects will be aligned and fitted by a professional prosthetist at A Step Ahead Prosthetics in Burlington, MA. No personnel at A Step Ahead Prosthetics will conduct research or have any vested interest in research outcomes or publication.

Attire:

Subjects will be asked to wear tight-fitting clothes, such as a skin-tight shirt, running shorts and low-profile shoes. If this is not possible, clothes will be provided according to subject needs. The investigators will provide and may require subjects to wear a skin-tight Velcro outfit that allows us to place reflective balls for video camera capture.

Location(s) and Timeline:

Experimental sessions will be conducted in the MIT Biomechatronics Laboratory (E14-274), 75 Amherst St., Cambridge, MA 02139. Any alignment and fitting of prosthetic devices will take place at A Step Ahead Prosthetics, 21 A. St., Burlington, MA 01803.

Total study duration is expected to be 8 hours per subject, likely over two 4-hour sessions. These sessions can be completed either in a single day or over two days. After subject selection, the entire study is expected to take 3 months.

Powered Prosthesis:

Subjects will be given two computer-controlled, powered ankle-foot prostheses to attach in place of their customary prosthesis during a session. These include the Blatchford Elan as well as a variable-stiffness prosthesis developed in the Biomechatronics lab. These powered prostheses have the capability of providing active assistance or changing mechanical properties during walking. Controls can be adjusted either through a wireless link or hardwire connection depending on the device. Subjects will be given as much time as necessary to practice using the prostheses before the experiments begin.

Passive Prosthesis:

Subjects will be given three passive prostheses to attach in place of your customary prosthesis during a session. These include the Ossur Pro-flex XC, a passive sliding-beam prosthesis, and a passive prosthesis that can change ankle equilibrium angle manually. Subjects will be given as much time as necessary to practice using the prosthesis before the experiments begin.

Data Collection:

Data collection is expected to take place in two segments. The first segment consists of level-ground walking on a treadmill at three speeds between 0.5-1.5m/s (slow to fast walking). At each speed, all five prostheses will be tested, randomly selected, for 2mins each. Motion will be captured with a VICON motion capture system, and ground reaction forces will be measured using a Bertec force-sensitive treadmill. For each speed, once all prostheses have been tested, each subject will be given a questionnaire to ascertain how each prosthesis performed at heel strike (early stance), roll over (mid stance), and powered plantar flexion (late stance). In addition, each subject will be asked how each prosthesis generally performed, and their personal preference. This testing will occur across the three walking speeds, resulting in three completed questionnaires.

In addition, subjects will walk in a figure-8 pattern at a preferred gait speed around two cones placed on the level-ground walking surface and separated by up to 30 feet. Subjects will perform the walking figure-8 for a minimum of 5 times for each randomly-selected prosthesis. Once all prostheses have been tested, each subject will be given a questionnaire to ascertain how each prosthesis generally performed, and their personal preference.

The second session will consist of slope and stair walking. Each subject will ascend and descend stairs and a ramp inclined between 4°-10° from horizontal at their preferred speed, in a randomly selected order. Motion will be captured with a VICON motion capture system, and ground reaction forces will be measured using a Bertec force-sensitive treadmill for slope ambulation, and a force-sensitive staircase for stair ambulation. All five prostheses will be tested, randomly selected. Subjects will perform each of stair ascent and stair descent for a minimum of 5 times per prosthesis. For slope ambulation on an instrumented treadmill, subjects will walk for a total of 2mins for slope ascent and 2mins for slope descent with each prosthesis. For each slope and stair ascent/descent, once all prostheses have been tested, each subject will be given a questionnaire to ascertain how each prosthesis generally performed, and their personal preference. This testing will occur across the slope terrain types, as well as after the stair ascent/descent trial, resulting in three completed questionnaires for each subject.

Inclusion Criteria:

• Person with unilateral transtibial amputation
• K3 or K4 Medicare mobility rating
• Ages 18-65

Exclusion Criteria:

• Below K3 Medicare mobility rating
• Outside of age range (liability and safety reasons)