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2011) using FES and a spinal cord injured person,
we have also found that the mean frequency
decreases during the periods of extension
maintenance. Therefore, the results presented in this
paper are consistent with studies already published
and show that this technique can be useful in
following the evolution of FES-elicited muscle
contraction. Convex hull area, despise its limitations,
can be a promising candidate as a parameter
indicating muscle fatigue in closed-loop FES control
systems.
5 CONCLUSIONS
In this study, we proposed the use of a computational
geometry technique known as the convex hull of a
finite set of planar points in the analysis of triaxial
mechanomyography signals. During an open chain
contraction and maximum knee extension evoked by
functional electrical stimulation, the convex hull
showed that its area reduced in all planes in a space
defined by the three axes of the mechanomyography
sensor. This reduction in the convex hull area was
related to a decrease in force production due to sup-
pressive performance phenomena like muscle fa-
tigue.
ACKNOWLEDGEMENTS
The authors thank CNPq, SETI-PR, CAPES e
FINEP for the financial support.
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