Inclusion Criteria:

• 7 control subjects with normal lower extremity function: mentally independent adults with intact extremities. These individuals shall have no significant medical history that would impair their ability to perform 3, repeated, sit to stand trials. Exclusionary examples might include history positive for total joint arthroplasty of the hip or knee and significant cardiomyopathy.

Control subjects will be non-amputee, generally healthy individuals, mentally capable of providing informed consent. They will have no significant medical history that could be perceived by investigators to hinder the ability to transfer. Anyone not meeting these criteria cannot be a control subject.

• 28 subjects with unilateral amputation at the level of the thigh. 7 each in four groups:

  1. Active Extension Group: Power Knee
  2. Microprocessor Stance Control Group: C-Leg, Rheo, Adaptive
  3. Non-Microprocessor Stance Control Group: Mauch, Catech or other stance control units
  4. Non-Microprocessor and Non-Stance Control units: WASB, polycentrics, pneumatics Each subject must have a prosthesis for which they have had for a minimum of 90 days in its present condition.

• All subjects must be:

  1. at least 21 years of age,
  2. mentally independent, and
  3. able to give informed consent.

Exclusion Criteria:

• Subjects are not candidates if they:

  1. are under 21 years of age
  2. are mentally dependent and unable to provide their own informed consent
  3. have worn the present prosthesis for less than 90 days in the current condition
  4. have bilateral amputation
• Subjects with an amputation are not candidates if they only use a prosthesis for transfers or therapy (K0 or K1 Medicare functional class). They must be independently ambulatory, at some level in the community (Medicare functional class "K2-K4"). They are furthermore not a candidate for this study if they have bilateral amputation (at any level) of the lower extremity as the purpose is to determine sound versus involved side loading, then against control. If all of the latter criteria are satisfied, the final piece is the 90 day prosthetic accommodation period. Candidacy then hinges upon the fact that they are accommodated to their current prosthesis as evident by having worn the current device, unaltered for the 90 days prior to testing.