Biomedical Engineering Reference
In-Depth Information
7.4 FES-EVOKED EXERCISE
Originally FES was used as a technique to achieve standing and stepping amongst
people with SCI (Vodovnik, 1965; Vodovnik, 1967). Individuals with SCI may be
facilitated to perform upright ambulation with FES — sometimes with the assis-
tance of orthoses. Nevertheless, the limitations in FES-evoked muscle contractions
and the technology have to date made it impractical for extended walking outside
of research laboratories (Kralj, 1989). However, more recently researchers have
realized the potential of FES to produce exercise for peripheral and cardiorespira-
tory benefits in people with SCI (Phillips, 1984; Mutton, 1997). Even though the
initial goal of FES for functional ambulation has yet to be achieved in a wider SCI
population, the health benefits of FES evoked cycling exercise was discovered and
has since been extensively acknowledged and investigated.
7.4.1 Benefits of FES-evoked Exercise
The health and fitness adaptation cycle continues as FES-evoked exercise is per-
formed regularly. The regular muscle contractions accompanied by increased
blood circulation can induce muscle hypertrophy which is also a well sought
after cosmetic benefit amongst paraplegics and tetraplegics who normally have
atrophied legs. An incomplete paraplegic may be able to perform better during
training sessions if their muscular and cardiorespiratory capacities were enhanced,
which might be a limiting factor before training (Postans, 2004). All these gains
have the potential to increase ones psychological and social health and adaptation,
which is important to reduce depression that is common amongst people with
disabilities.
Increasedmuscle mass and size following electrical stimulation directly results
in increased muscle strength and endurance (Kagaya, 1996), which further lead to
increased functional exercise capacity (Petrofsky 1992a; Petrofsky, 1992b). With
FES-evoked training, persons with SCI can perform exercise for longer training
duration, at higher cadences, and increased resistance loads. Consequently, as
FES-evoked functional capacity increases (i.e. evoked stepping distance, time
or endurance), individuals who perform FES-evoked exercise will be able to
exercise at higher cardiorespiratory intensity and eventually increase their aerobic
fitness (Raymond, 2002). In short, carefully prescribed, FES-evoked exercise has
demonstrated the ability to increase physical activity, life satisfaction, and well-
being of people with SCI.
7.4.2 Performance Control
Research has been conducted to overcome the rapid muscle fatigue associated
with FES that has limited the intensity of evoked exercise sessions. One way to
overcome rapidmuscle fatigue is to employ feedback control of the system. A user-
controlled open-loop system is the most basic type of FES-system control, which
