IEEE Robotics & Automation Magazine - December 2017 - 64

the exact causes of the fracture are still unknown, the immediate effect was an abnormal increase in muscle spasticity,
which prevented proper performance of our control system.
The pilot received warnings from the referees when he
attempted to assist lower limb motion using his hands as
spastic movement occurred, a practice not allowed in the
competition; this resulted in his termination as a racer. The
performance the pilot obtained in the final round was surprisingly similar to that of the first round, i.e., a fast start
followed by spastic behavior, which prevented smooth control of cyclic movement.
After the competition, the pilot underwent surgical treatment, which resulted in preservation of his quadriceps and
knee function. He has since recovered muscle force on the
affected leg and regularly uses electrotherapy.
Discussion
In this article, we reported the development of a novel FES
cycling platform, as well as a case study of a preparation protocol designed to introduce individuals with SCI to FESassisted physical exercise and, in particular, to enable our
pilot's participation at the Cybathlon 2016 FES bike race. We
introduced new approaches to common problems encountered in mobile FES cycling. For instance, we used wireless
sensors to measure crank movement instead of encoders
attached to the crankset. Although simple, this modification
enables faster adaptation of commercially available recumbent tricycles to mobile FES cycling. In addition, we developed commands to increase the user's independence during
operation. Employing a simple interface with buttons, the
pilot is able to trigger a sequence of FES patterns to escape
dead zones. Finally, we opted for a recumbent trike that features a different geometry than other teams that took part in
the competition. Our trike presents an intermediate geometry between seated and fully recumbent positions, representing an attempt to provide more comfort and visibility to the
pilot, but also reducing the biomechanical deficit in seated
positions. However, in our case, the pilot reported he was
sliding on the seat in some cases, possibly affecting the
resulting cycling movement.
Additional innovations in our project involve the tools
used for control design. We employed both detailed musculoskeletal simulations and stationary trials in which quantifiable disturbances that emulate the load changes in different
terrains were applied. Both strategies targeted improving the
dynamic response of our control system, including the transient response for fast gear switching.
Based on our experience at the competition, we learned
that we should have also focused on procedures to improve
pilot endurance. Indeed, the accelerated onset of fatigue
induced by FES is an important limitation to FES-assisted
physical exercise for individuals with SCI because it may
reduce the quantity and quality of performed exercise.
The first measure in coping with fatigue is to establish both
longer cycling sessions and training protocols designed to
play a major role in muscle adaptation, an approach adopted
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IEEE ROBOTICS & AUTOMATION MAGAZINE

DECEMBER 2017

by other teams at Cybathlon. In addition, alternative stimulation strategies, such as reduced FES frequency throughout
the training protocol, may be used, possibly adopting even
lower frequencies (as in [6], for instance). An alternative that
may prove equally effective for extending exercise duration
and increasing muscle-elicited force is the asynchronous
stimulation of motor units within a muscle group [18], a
technique in which lower FES frequency is used in association with a high number of stimulation channels.
Finally, in view of the potential risks involved in mobile
FES cycling, the project results allow speculation regarding
other measures that could limit these associated dangers.
For instance, most teams employed lower cycling cadences;
these may be an effective strategy to reduce muscle spasticity [19](an issue we encountered in our later training sessions) and also to reduce the interaction forces between
limbs and the tricycle which may result in excessive force on
skeletal structures. In biomechanical studies using finiteelement models, we have concluded that FES-induced muscle force alone does not present a risk of fracture if bone
density recommendations are respected. Nevertheless,
because it is a closed kinetic chain exercise, forces may
increase in structures such as the patella, particularly if
external forces are applied (e.g., hand pushes). Hence, those
should be avoided.
Conclusions and Current Challenges
The use of FES-assisted physical exercise by individuals with
SCI may provide effective functional benefits. The Cybathlon FES bike race is a unique opportunity to evaluate different FES cycling platforms, in terms of both technological
development and training protocols for individuals with
SCI. The race features radically different solutions, ranging
from FES cycling platforms similar to wheelchairs to
implanted FES systems.
In our work, we have focused on developing a new stimulation system for mobile FES cycling based on an adapted,
commercially available tricycle, as well as a training protocol
based on limited total duration. The obtained results indicate
that the developed technology may be used for long-term
FES-assisted mobile cycling exercise but that the training protocol should include adaptations to enable the development of
muscular endurance. Our current effort is focused on performing a long-term evaluation of our FES cycling platform
on a larger population.
Acknowledgments
We thank Estevão Carvalho Lopes for his complete dedication to this project. The project was also managed by Núcleo
de Tecnologia Assistiva, Acessibilidade e Inovação, directed
by Emerson F. Martins, and hosted in Associação de Centro
de Treinamento de Educação Física Especial, directed by
Ulisses Araújo. We deeply thank both directors. Scientific
collaboration with Team Free Wheels was essential, particularly concerning the control and training protocol design,
and thus team manager Christine Azevedo-Coste and

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - December 2017