Biomedical Engineering Reference
In-Depth Information
M
x
and M
y
. Since at every instant, the actual foot plantar area in contact with
the platform surface varies, the signal obtained is an overall response of the
deformation. These force and torque are averaged values related to the instantaneous
area of contact. Even though, force platforms represent the only commercially
available system capable of measuring the complete GRF vector
Using pressure insoles or platforms, the type of information obtained is different.
These can map the pressure distributed in the whole plantar surface, which is
of great relevance when the main purpose is the foot instead of the movement
itself. Depending on the model and manufacturer, these systems can have a spatial
resolution varying between 1 cm [pedar
®
]and1mm[Xsensor
®
], which determines
the plantar pressure mapping discreteness. Commercially available platforms have
always a better resolution than insoles. This mapping provides a more detailed
picture on the evolution of the force distribution for each area in contact at every
moment, instead of an overall value as with the force platforms. Nevertheless, the
drawback is the fact of measuring only the GRF vertical component. This aspect
associated to the difficulty of developing a system or sensor capable of measuring
the three plantar force components, simultaneously and locally, either inshoe or on
the floor surfaces, have been subject of research for several decades.
In his revision work on sensors to measure plantar pressures [
45
], Stephen Urry
refers that, considering the various attempts to measure shear plantar forces and
the difficulties and limiting factors encountered by researchers, this task is an even
more exigent and time consuming than pressure measurement. One interesting point
of view of this author is that the optimum sensor is not the one with the best
performance and technological characteristics in the point of view of engineers,
but the one adjusting the best to the purpose for which it was developed, i.e., taking
into account the application and its limitation is as important as developing a sensor
with outstanding technical characteristics. Therefore the optimal solution is a natural
commitment between these two aspects.
To measure horizontal or shear plantar force components, sensor measurement
range should be chosen to represent between 20% and 26% the body weight, since
according to Lebar et al., this is the expected magnitude for these components [
25
].
2.2
Research Developments
2.2.1
Measuring Plantar Pressures
In research, the first instrumented shoe, identified by the authors as
“CyberShoe”
[
35
], was a prototype incorporating a variety of different sensors, allowing the mea-
surement of angular velocities with gyroscopes, accelerations with accelerometers,
pressures in pre-determined areas using piezoresistive sensors and contact instants
with piezoelectric sensors. This prototype was developed with a broader concept
since it was designed to be applied in dancers in order to follow their steps and
movements and correlate this information with the music played.
