Functional Electrical Stimulation Leg Exercise: From Technology to Therapy - Biomechatronics in Medicine and Healthcare - page 99

7.5.5 Isokinetic FES Leg Stepping Exercise

A more recent approach towards maximizing FES-evoked leg exercise dose po-
tency has been to employ an elliptical stepping movement (Hamzaid, 2009).
An isokinetic FES leg stepping trainer (iFES-LST) was developed to integrate
the features of isokinetic exercise with evoked muscle contractions and elliptical
stepping movements (Hamzaid, 2009). The stepping movement had less vertical
displacement than normal cycling would have and had greater ratio of horizon-
tal:vertical displacement (Hamzaid, 2007). The authors hypothesised that the
evoked muscle contractions would facilitate longer muscle activation times to
produce the elliptical movement (Hamzaid, 2006), facilitated by a 'slider-crank'
mechanism (Shigley, 1995) as illustrated in Fig. 7.4 . Thus, leg training might
approximate the known movements of walking, but in a seated posture, with
potential benefits to the patient.
The primary leg muscles were stimulated in repetitive sequence based on
the position of the legs. A continuous potentiometer was utilized to deduce the
accurate crank angular position from which the leg position was derived. Evoked
leg muscle contractions translated into the legs producing stepping power onto
the pedals, which could be quantified given the muscles were conditioned enough
and the stimulation current is sufficiently high.
The elliptical stepping trainer elicited greater metabolic cost and higher me-
chanical efficiency compared to traditional FES-evoked cycling (Hamzaid, 2009).
The gain in power production by changing the mechanical foundation (i.e. cycling
to stepping) was greater than the power production increase when optimizing the
stimulation pattern during FES-evoked stepping (Hamzaid, 2008).
Another feature of the iFES-LST was the released ankle joint in plantar-
dorsiflexion facilitated by a custom-made ankle foot orthoses (AFO). The AFO

Quadriceps

Hamstrings
Gluteals

Elliptical stepping path

Rotational crank movement

Linear slider movement

Figure 7.4 Joint and linkages of an elliptical stepper. Primary muscles and the muscle
stimulation path is illustrated. For color reference, see page 217.