Reactive foot placement in balance control during standing and walking in healthy young adults and stroke survivors.

In daily life the upright human body is continuously challenged by external
disturbances, such as gravitational forces and forces originating from
interactions with the environment. These disturbances can lead to a loss of
balance, which must be acted upon accordingly to prevent a fall. Following a
disturbance, proper foot placement is crucial for maintaining balance during
both standing and walking. However it is unclear why humans place their foot at
a certain location at a certain time following an unexpected balance
disturbance. A model based prediction of a suitable foot placement location to
maintain balance and prevent falls can have great value in both clinical and
robotics fields of research. Investigating foot placement in stroke patients
can lead to a better understanding how stroke related complications affect foot
placement, and how these might be compensated using supportive devices such as
exoskeletons or balance keeping devices. The latter are wearable and portable
robotic devices developed with the aim of detecting the subject*s loss of
balance and of providing corrective actions to avoid or delay the risk of
falling. An open research topic related to the development of these devices
deals with assessing their effectiveness by evaluating how human balance
performance changes by using supportive devices.

The goal of the research is to apply balance perturbations during standing and
walking, and capture the resulting stepping responses. These data will be used
to develop and verify predictive models of foot placement. Such models might
eventually be incorporated in rehabilitation or balance assisting devices.
Another aim of this study is to assess how the balance keeping performance of
subjects changes by using a supportive device. An inertial flywheel actuator
has been designed at UT to assist subjects in keeping balance in the frontal
plane. The effectiveness of the device will be evaluated by comparing the
balance keeping performance of subjects when they wear and when they do not
wear the inertial flywheel actuator.

The study is designed as a non-invasive cross-sectional intervention study to
assess foot placement for the control of balance during standing and walking.
The effectiveness of the inertial flywheel actuator in supporting subjects to
keep balance in the frontal plane will be also evaluated. It consists of two
main experiments, one in standing and one in walking, each consisting of one or
more sessions. The test conditions within a session will be randomized. Healthy
subjects might be asked to participate in an additional session with altered
conditions that were not captured in the main session. Stroke survivors will
only participate in the main session.

Balance will be perturbed during standing and/or walking by applying sudden
forces of various magnitudes and duration at the pelvis, and by sudden
movements of different magnitude and speed of the belts of the treadmill..
These perturbations are applied using two external devices: the pelvis
perturbator and the treadmill. The disturbances are sub-maximal. They challenge
the subject to make a corrective step, but do not have the goal to make them
fall.

All experiments are non-invasive procedures involving disturbances similar to
those that could occur in daily life. A single experiment will require
approximately 45 minutes of active participation for healthy subjects, and
approximately 12 minutes for stroke patients. This is not expected to put
extensive load on the subjects. All subjects can take rests during the
experiment and participate on their own pace. Risks leading to injury of the
subject are low, given the safety precautions. The study does not lead to any
direct benefits for the subject, but may lead to a better understanding of
stepping responses in human balance control and it may prove that the inertial
flywheel actuator improves the human balance performance. This knowledge might
be applied in both clinical and robotics fields of research.
Stroke survivors will be included to characterize balance control specifically
related to the complications occurring after stroke. Understanding in which way
these complications hamper balance control might lead to better methods of
support, e.g. during rehabilitation.