Biomedical Engineering Reference
In-Depth Information
individual during the day using portable sensors:
accelerometers, for example, are used to count the number of
steps taken by a child with cerebral palsy during the day
[ISH 13] or even to monitor the physical activity of patients
after a stroke [GEB 10], inertial measurement units assess
the physical activity of patients with Duchenne muscular
dystrophy at home [JEA 11]. Motion analysis systems used
in the public domain are also often involved in rehabilitation.
In particular, the system Kinect™, combining a video
camera and a depth sensor, appears to be useful for the
functional assessment of patients performing standardized
exercises [BON 14].
This topic deliberately focuses on the kinematic analysis
of motion, i.e. the quantified description of the movement of
different joints in the human body. It is clear that this point
of view is simplistic for those who want to understand
motion, but it is an essential first step to master to properly
address the other elements. In particular, most of the time,
kinematic motion analysis systems are coupled with other
measurement techniques, such as force sensors (force
platforms in the case of gait analysis) and/or systems that
record muscle activity (electromyography). These additional
data help us understand the dynamics of motion, that is to
say, to link the movements to their cause: mechanical
actions. However, for this type of analysis, different models
must be used, with their set of more or less realistic
hypotheses. For example, it is possible to calculate the
moment for each joint resulting from all the mechanical
actions, by using inverse dynamics from the external forces
measured, but this calculation involves defining the
distribution of mass in the different body segments (mass,
position of center of gravity and inertia matrix) which is
source of new uncertainty. If we wish to go further and
assess the contact forces at the joints, for example,
