The purpose of this study is to examine the path and velocity of the center of mass (CoM) and center of pressure (CoP) during double support of persons walking with a unilateral above-the-knee prosthesis and determine the effects of prosthetic foot stiffness and effective length on CoM and CoP.Persons with a lower limb amputation walk with compensatory movements that affect the smooth trajectory of the center of mass (CoM) during weight transfer. The lack of control in the foot/ankle complex reduces fine motor movements, influencing the progression of the CoM and transfer of ground reaction forces represented by the center of pressure (CoP). Without control of the ankle joint, prosthetic users "fall" off of their trailing prosthetic limb during weight transfer, resulting in much more abrupt CoM and CoP transfers from trailing to leading limb. These abrupt movements during transfer not only increase stress on the sound limb, but also decrease the subject's energy efficiency during ambulation. The current study will further examine the CoP path and velocity in relation to the CoM path and velocity during double support of men with a transfemoral prosthesis, as well as explore how prosthetic foot ankle stiffness and effective length affects the CoP path and velocity.

Inclusion Criteria:

• Participants must have a transfermoral amputation and use an above-the-knee prosthesis with an articulating knee joint on a daily basis.
• Participants must be male.
• Age greater than or equal to 18 years, but less than 65 years.
• Participants must have no known pathology or comorbidites that would affect their ambulatory ability
• Ability to tolerate walking for a minimum of 100 yards over the course of a two and a half hour time period.
• Ability to walk one block without needing to rest.

Exclusion Criteria:

• Use of ambulatory aids such as canes or crutches.
• Any medical or psychosocial condition that, in the opinion of the investigator, could jeopardize the subject's participation, and compliance with the study criteria.
• Bilateral amputations.

Persons with unilateral transfemoral amputation who are ambulatory with a prosthesis and no assistive device.