Robotic Assessment of Lower Extremity Motor Learning

Current rehabilitation assessment techniques make it difficult to monitor the day to day
changes in patient functional abilities. In an ideal setting, one would like to be able to
observe how subtle changes in the way that therapy is delivered affects the manner and the
time it takes patients to learn the adaptations necessary to recover lost function. To this
end, the investigators seek to apply a paradigm that has been used to study motor learning
in the upper extremity (the FFAP) to the Lokomat gait orthosis platform. Over the last
decade the FFAP has been used to elucidate the mechanisms and processes that contribute to
motor learning in the upper extremity. The broad acceptance of this paradigm within the
motor control community sets a precedent for application to the lower extremity and its use
in clinical environments.

Implementation of the FFAP in the Lokomat system will allow motor learning to be assessed
during lower extremity motor tasks. Such a tool could be used to systemically assess the
effectiveness of different aspects of therapy, such as the effects of training session
duration, number of exercise repetitions, inter-trial (inter-session) intervals, and
magnitude of perturbation.

In this initial pilot, the investigators seek to apply our Lokomat implementation of the
FFAP to healthy adult subjects in order to understand the feasibility of this approach and
form a database of healthy subject learning rates. This initial step will allow us to bridge
the scientific gap between lower extremity and upper limb motor learning research, while
yielding data that can serve as a basis of comparison for future studies with patients.
Additionally, such a methodology would suggest new avenues of research for lower limb motor
learning and create an increased understanding of the motor principles that govern the
spectrum of human movements.

Ultimately, by understanding the fundamental motor learning principles that drive
neurorehabilitation the investigators can better understand what makes rehabilitation
successful and attempt to better improve current rehabilitation protocols.

Before the testing session begins, the subject will be placed within the Lokomat by securing
subjects at the trunk, pelvis, and lower extremities using adjustable cuffs with Velcro
straps, so that the hip and knee joints are aligned to those of the Lokomat. Each testing
session will begin with walking for approximately 5 minutes in the standard clinical mode of
operation.

Optional use of body weight support and foot straps can be used to ensure subject is walking
comfortably within the Lokomat. Clinical mode allows subject to be walked by the Lokomat
along a predefined trajectory with the pace of the treadmill matched to the robotic legs.
After subject has acclimated to Lokomat walking, the motor learning experiments will begin.
The format of the motor learning experiments is as follows:

- "Free-run mode"- Subject walks as normally as possible within the Lokomat, while the
Lokomat compensates for its own weight, but does not restrict the subject's movements.
Subject's walking pattern is recorded as the baseline movements of the experiment.

- Force field mode- Subject experiences small force perturbations from the Lokomat. These
forces are perpendicular to their path (moving the foot upward), velocity dependent,
and occur primarily in swing phase (when velocity is greatest). These forces are able
to slightly alter the subject's walking trajectory. This generates error which drives
the motor learning system and causes adaptation, which takes the form of compensatory
forces equal and opposite to the force field. It is important to note that any forces
outside the standard Lokomat safety range will not be experienced by the subject since
the standard safety limits for clinical use remain present in the device.

- Error clamp mode- Similar to the clinical mode, where the subject is limited to walking
along a predefined trajectory, during the error clamp mode, the subject is required to
walk along their average baseline trajectory (recorded during the Free-run mode), but
can do so at the speed of their choosing. Error clamp trials are interspersed between
force field trials, and used to measure adaptive compensatory forces. Any forces not
used to move the subject along the path are instead compensatory forces that reflect
the subject's adaptation. These forces can be measured throughout the experiment and
used to infer the subjects' rate of learning.

Inclusion Criteria:

- Males and females, healthy adults age 18-55 years, with normal gait.

Exclusion Criteria:

- Lower extremity fractures

- Current or previous history of orthopedic injury that would prevent safe use of the
Lokomat

- Body/femoral length size beyond the limits of Lokomat robotic arm (femur length
between 350-470mm)

- Body weight > 135kg (~298 lbs) maximum limit of the body weight support system

- Skin lesions on the lower extremities

- Cardiovascular or pulmonary contraindications

- Motor system or proprioceptive impairments

- Severe cognitive impairments that would prevent the use of the Lokomat