One Solid Ankle Cushion Heel (SACH) and two Dynamic Elastic Response (DER) prosthetic feet will be tried six times in random order by the patient. The patient will be an active prosthetic foot user who walks several kilometers per day and was amputated at the trans-tibial level because of injury. Gait pattern will be rated in comparison with the patient's previous prosthetic foot by a physiatrist, physiotherapist, prosthetist and the patient. One-leg standing and 10-meter walking tests will also be performed.

The prosthetic feet will be: one SACH foot (by Otto Bock - foot C, advertised for activity category 1) and two DER feet (Dynamic Motion by Otto Bock - foot B, advertised for activity category 2-3; and Triton by Otto Bock - foot A, advertised for activity category 3-4).

All the prosthetic feet are of the same size and chosen for the patient's weight. They will be covered so that neither the patient nor professionals will be able to see which prosthetic foot is being used.

The study is blinded because the prosthetist designated for changing the prosthetic feet will be the only one who will know which prosthetic is being used. The orientational sample size calculation and the randomisation plan were prepared by a statistician.

The first trial will be performed using the patient's own prosthetic foot in order to establish a baseline. The patient will then have to to compare the prosthetic feet with his own existing prosthetic foot and rate the ability to walk on even terrain (100m), uneven terrain (grass, 100m), decline and incline (i.e., slope), and up and down the stairs (one floor) on a five-point Likert-type scale (-2 much worse, -1 slightly worse, 0 the same, 1 slightly better, 2 much better). After each trial he will also perform the one-leg standing test (with three repetitions) and the 10-meter walking test. Before each trial, the patient will be given 15 minutes for adaptation to each new prosthetic foot without the presence of the assessors.

The three expert observers will be: a physical and rehabilitation medicine specialist physician, a certified prosthetist-orthotist, and a physiotherapist. Each has got over 20 years of experience in rehabilitation of patients after amputation and observation of their gait. They will be blind to the currently used prosthetic foot. They will follow the patient and assess his walking using the same rating scale in comparison with the initial trial as the patient.

Inclusion Criteria:

• active prosthetic foot user who walks several kilometers per day
• amputation at the trans-tibial level >5 years ago

Exclusion Criteria:

• other medical problems