The objective of this clinical study is to examine the acute kinematics and kinetics of utilizing the Tibion Bionic Leg in a sample of chronic post-stroke patients performing sit-to-stand and stand-to-sit transfers across a range of assistance and resistance settings (internal to the device); to compare these metrics to baseline performance without the Bionic Leg; and to determine the Bionic Leg settings that optimize a restorative (equal force distribution) movement state in these patients.

Comprehensive motion (kinetics and kinematics) data specific to sit-to-stand and stand-to-sit transfers with and without the Tibion Bionic Leg. The Vicon Motion Analysis System will be utilized to track movement using markers on the subject and the Bionic Leg per the UCSF Human Performance Center's routine. Once outfitted with the marker system, patients will be instructed to perform multiple sit-to-stand and stand-to-sit transfers while data is gathered.

The sit-to-stand and stand-to-sit transfers will be performed using a standard chair, with a seat height not less than 12" from the floor. The chair will be positioned such that, at sitting rest, each of the subject's feet are positioned on limb-specific force plates (left and right).

Inclusion Criteria:

• Single ischemic stroke with residual unilateral lower-extremity weakness
• Chronic post-stroke (>12 months since event)
• Eligible to participate to lower extremity physical therapy
• Age 30 years or greater
• Able to ambulate at least 10 meters without therapist assistance
• Able to ambulate without a leg brace
• Able to transfer from sitting to standing without physical assistance from a therapist
• Able to transfer from standing to sitting without physical assistance from a therapist
• Subject must understand the nature of the study and provide written informed consent prior to enrollment.
• Subject must be willing and able to attend all study sessions

Exclusion Criteria:

• Medically unstable
• Age younger than 30 years
• Subacute post-stroke (< 12 months since event)
• Status-post multiple strokes
• Status-post traumatic brain injury
• Not eligible to participate in lower extremity physical therapy
• Concomitant degenerative neurological conditions
• Not able to ambulate at least 10 meters without therapist assistance
• Unable to ambulate without a leg brace
• Unable to transfer from sitting to standing without physical assistance from a therapist
• Unable to transfer from standing to sitting without physical assistance from a therapist
• Unable to follow instructions, complete follow-up, or provide informed consent.
• Currently enrolled in another investigational device or drug trial