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Fig. 1 | Journal of NeuroEngineering and Rehabilitation

Fig. 1

From: The effects of FES cycling combined with virtual reality racing biofeedback on voluntary function after incomplete SCI: a pilot study

Fig. 1

a Block Diagram of iCycle. The cadence control sets the voltage applied to the DC motor. The measured torque-cadence curves are shown in (d); the stiffness was made intentionally low to avoid musculo-skeletal damage. When the torque is positive, the power supply is absorbing power which is dissipated in a heat sink. Stimulation was applied during alternate revolutions of the pedals and the output of the torque transducer is averaged over revolutions without stimulation to give the signal called effort. For each of the six stimulation channels, the output was gated so that the 30 Hz pulses were applied from a switch-on to a switch-off angle, which could be set for each participant. A commercial virtual reality cycling game was adapted for the iCycle. The hardware interface for this game has an output which is approximately the slope of the road in the rolling scenery. This slope is subtracted from the effort and the difference frequency-modulated by a voltage-controlled oscillator (VCO) before being fed back as the wheelspeed. There is also a pulse signal for every revolution of the crankshaft which is switched on to start the game and synchronises the avatar’s pedals with the real pedals. The VCO has an S-shaped characteristic, shown in (c), which limits the avatar’s speed to 0–12 m/s. The controls labelled effort, offset and slope are used to set the working range as indicated below the graph. The feint lines in (d) are the function where V is the voltage applied to the motor, T is the torque (N.m) and Ω is cadence (r.p.m.). The iCycle can deliver or absorb 30 W. b The iCycle is used with participants sitting in their own wheelchairs in front of the VR screen

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