Improving gait stability; the effect of step length and step frequency manipulations on the margins of stability in stroke patients.;Amendement on: Evaluating the risk of falling during gait: Which strategies do stroke-patients and transtibial amputees use to maintain dynamic stability and gait adaptability?

With their high incidence and associated costs, falls in patients form a
considerable problem in modern society. Despite the importance of this problem,
until now there is no univocal protocol to evaluate the risk of falling during
a rehabilitation process. To prevent falling, patients have to be stable during
steady state walking and capable to adapt their gait pattern when required by
the environment (e.g. to avoid an obstacle or to walk over uneven terrain). By
manipulating these concepts of walking structurally, and measuring the effect
of these manipulation on performance measures related to dynamic stability and
gait adaptability, the risk of falling can be quantified. But, probably more
important is to get an overview of the strategies patients use to withstand
these manipulations, because these strategies will give us information about
the effort of the patients to maintain a certain level of gait stability and
adaptability, which can be used for further treatment. Examples of strategies
are adaptations in walking speed and different step parameters like step
length, step frequency, and step width.

AMENDEMENT:
The results of this previous experiment showed us that stroke patients seem to
have more difficulties, compared to able-bodied people, with adapting step
frequency and step length, while preventing a decrease in walking speed, which
limits their ability to control and preserve their backward margins of
stability. However, based on the results of our previous study it is not yet
possible to conclude whether the observed adaptations in the gait pattern
reflect the inability to adjust the gait pattern adequately or reflect a
voluntary, but maybe incorrect, response of the patient. Information about this
aspect of walking in stroke patients would help us to better understand which
aspects of the walking pattern should be trained in the rehabilitation of
walking of stroke patients.

The objectives of this study are to investigate:
- which strategies patients use to maintain gait stability and gait
adaptability;
- whether the strategies used by patients to maintain gait stability and gait
adaptability, differ from strategies used by healthy people;
- and whether gait adaptability and dynamic stability differ between patient
and healthy controls.

AMENDEMENT - Additional experiment

The objectives of the additional experiment are to investigate:
- whether stroke patients are able walk at different combinations of step
frequency and step length at the same walking speed.
- whether these subjects are able to increase walking speed by increasing step
length and step frequency independently.
- how the different combinations of step length, step frequency at the same
walking speed will influence the size of the sideward and backward margins of
stability.
- how the increase in walking speed by an increase in step length or by an
increase in step frequency will influence the size of the sideward and backward
margins of stability.

During this experiment subjects will complete 3 trials of 4 minutes walking on
a treadmill, placed in a virtual environment (CAREN). The conditions are (1)
unperturbed walking, (2) walking with a balance perturbation and (3) walking
while executing an additional task. The balance perturbation will exist of
medio-lateral translations of the walking surface following a multi-sine
function. During the additional task, targets will be projected within the
virtual environment. Subjects will be asked to hit the targets with their
knees, as accurate as possible. During all experimental trials the treadmill
will be set in the self-paced mode, which means that subjects can determine
their own comfortable walking speed by moving forward or backward on the
treadmill. Before the experiment will start, subjects will perform a couple of
warming-up trials to practice with the experimental conditions. During the
experiment markers will be attached at the feet, legs, and pelvis of the
subjects. A Vicon infra-red camera system will be used to register the
movements of these markers.

AMENDMENT - additional experiment:
During this experiment subjects will complete 6 trials of 2 minutes walking on
the treadmill. By giving visual feedback subjects will be asked to walk at
different combinations of step length and step frequency. The experimental
conditions are:

1. A trial at comfortable walking speed, step frequency and step length.
2. A trial at comfortable walking speed, at 90% of comfortable step frequency
and at 111% of comfortable step length.
3. A trial at comfortable walking speed, at 111% of comfortable step frequency
and at 90% of comfortable step length.
4. A trial at 111% of comfortable walking speed, at 100% of comfortable step
frequency and at 111% of comfortable step length.
5. A trial at 111% comfortable walking speed, at 111% of comfortable step
frequency and at 100% of comfortable step length.
6. A trial at 123% comfortable walking speed, at 111% of comfortable step
frequency and at 111% of comfortable step length.

Subjects will walk 3 times during 4 minutes on a (self-paced) treadmill, at
comfortable walking speed. During one of these trials balance will be perturbed
by translating the walking surface. During another trial subjects will execute
an additional task during walking. To prevent falling, subject will wear a
safety harness, and one of the investigator will stand close to the subject to
assist if necesarry. The system has an emergency stop, which can stop the
complete system. With these precautions the risk of falling and injury is
minimized. Participation in this research does therefore not include serious
risks.

AMENDEMENT - Additional experiment:
Subjects will walk 6 times during 2minutes on a treadmill. During 3 of these
trials will walk at comfortable walking speed, during the other 3 trials
subjects will walk slightly above comfortable walking speed. During these
trials subjects will be asked to walk at different combinations of step
frequency and step length, with the help of visual feedback. For this
additional experiment the same security will be utilized as described above.