Biomedical Engineering Reference
In-Depth Information
In general, gait analysis is performed using force or pressure platforms to
acquire kinetic data, namely ground reaction force information, which associated
to video capture and inverse dynamic analysis will provide complete kinematical
characterization [
12
]. Also, by introducing the movement recorded in video to
a biomechanical model, it is possible to develop further biomechanical studies
[
33
,
47
].
2
Measurement of Plantar Forces
2.1
Commercially Available Systems
Every time the primary interest is measuring plantar forces for describing a certain
movement, the first experimental technique chosen will be using a force platform.
If, in addition, there is a need to characterize plantar pressure distribution, namely,
in order to study the contact between the foot and the ground or shoe during stance
phase, the common choice will be using pressure platforms or pressure insoles.
On the other hand, when choosing either platforms or insoles, measurement
conditions will be the relevant factor. When using platforms, it is common to ask
subjects to walk for a few minutes in order to warm-up, and also to adjust their steps
and velocity to get the foot right into the middle of the platform. This preparation is
considered to have some influence on the subject normal gait. If using insoles, this
problem will not exist, since the patient can walk freely without worrying where
to step on. The measurements can be taken anytime, and superfluous information
can be disregarded. This system is of particular interest in the study of foot-shoe
interaction, providing important information for orthoses design. Another advantage
is the fact of being a portable system, which can be taken for outside studies or other
type of movements, like running and dancing, for example. The negative aspect is
that fact that due to in-shoe conditions like, humidity and temperature, these systems
have a shorter lifetime.
Either force or pressure platforms or pressure insoles are commercially available.
Some examples are Bertec Corporation, Kistler Corporation, AMTI-Advanced
Mechanical Technology, Inc. force platforms, pedar
®
, footscan
®
and F-scan
®
pres-
sure insoles and also pressure platforms solutions from novel, RSscan International,
Tekscan
®
and Xsensor
®
Technology Corporation.
Force platforms provide Ground Reaction Force (GRF) measurement in terms of
its components: medial-lateral, anterior-posterior and vertical. The latter represents
the pressure exerted during contact in a certain instant. The other two components
represent the in-plane force component, which is related to the lateral deviation and
the direction or movement progression. The force components values are obtained
with the signal from four sensors located at the four corners of the platform, by
measuring their local deformations. With these instantaneous signals, the system
calculates the three force components F
x
,F
y
and F
z
, and the three torques M
z
,
