Inclusion Criteria:

• has a unilateral (one leg) transtibial (below-knee) amputation
• has used a prosthetic limb for walking for at least six months
• has a comfortably fitting prosthetic socket
• has a removable prosthetic foot attachment (i.e., is not rigidly attached to the back of the socket) so it can be used with study prosthetic feet
• be able to walk with a prosthetic limb sufficiently to participate in the experiment walking trials

Exclusion Criteria:

• contralateral limb or upper limb amputation that would interfere with completion of study activities
• are unable to use more than one of the test feet for any reason (e.g., excessively long residual limb that is not compatible with wearing study prosthetic feet)
• unable to walk under the minimal necessary study walking conditions in order to complete the study procedures without undo stress
• current surgical, neurological, rheumatologic, or lower limb musculoskeletal problem that significantly impairs ambulation (e.g., current ulcer, terminal illness)
• weight greater than 263lbs.
• inadequate cognitive or language function to consent to participate
• currently incarcerated
• impaired decision-making ability or the use of a legally authorized representative