Biomedical Engineering Reference
In-Depth Information
is mostly employed during FES-evoked standing, stepping or short ambulation.
In an open loop control the system does not change its stimulation properties
regardless of the user's responses or performance, such as muscle fatigue when
exercising or knee buckling during standing unless the user presses a switch (Kralj,
1989). Therefore, the only feedback the system has is the user's input which is
based on the user's perception of their performance.
FES-evoked cycling exercise employs closed-loop control as it modifies the
stimulation parameters based on training time, pedal or leg position, and in
some modes based on the evoked forces. Position or motion sensors could be
integrated as part of the closed loop system to detect critical body position or
joint angles (Braz, 2006). Another example is the use of EMG to provide a signal
that would indicate the initiation point during the start of an activity amongst
people with incomplete SCI (Dutta, 2009). Surface EMG might also be utilized
to detect early onset of muscle fatigue as a mode of fatigue compensation control
(Winslow, 2003). The closed-loop systems allowed the stimulation parameters to
be minimized and increased only as required to maintain a certain movement or
position. This delayed the occurrence of muscle fatigue thus prolonged a training
session (Winslow, 2003).
7.5 TECHNICAL DEVELOPMENT OF FES EXERCISE MACHINES
7.5.1 FES Cycling
FES-cycling elicits leg muscle contractions in appropriate sequence to produce
cycling motion (Petrofsky, 1984; Wilder, 2002; Petrofsky, 2003). Generally the
quadriceps, hamstrings, and gluteal muscle groups are used during FES-cycling
(Glaser, 1994). Muscle contraction timing is controlled by a computer that stim-
ulates each of the muscles at the correct crank angle to produce a pedalling
movement (Petrofsky, 1984).
As the most popular mode of FES-evoked exercise, FES-evoked cycling may
be the most economical way of training the leg muscles, and suitable for a wide
range of persons with SCI. During FES cycling, the patient's body weight is always
supported by seating and the training is highly repetitive. Furthermore a simple
controller can automate the session. Therefore, only one person is required to
monitor and run the system, making FES cycling a convenient and efficient mode
of exercise for SCI individuals. A SCI person can begin FES-evoked cycling
without much pre-training, in comparison to FES-evoked standing or walking
which needs the leg muscles and bones to be strong enough to bear body mass
in an upright posture.
In the past, FES cycling ergometer designs were dominated by devices that
relied upon the electrically stimulated muscles to provide pedal drive and a
mechanically or electrically braked flywheel to provide resistive loading. Over the
years, advances have been made to the electronic braking and stimulation systems
(Chen, 1997). However, controlling cycling cadence in this manner becomes more
 
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