Distributed low-frequency functional electrical stimulation delays muscle fatigue compared to conventional stimulation.

We present a low-frequency stimulation method via multi-pad electrodes for delaying muscle fatigue. We compared two protocols for muscle activation of the quadriceps in paraplegics. One protocol involved a large cathode at 30 HZ (HPR, high pulse-rate), and the other involved four smaller cathodes at 16 HZ (LPR, low pulse-rate). The treatment included 30-min daily sessions for 20 days. One leg was treated with the HPR protocol and the other with the LPR protocol. Knee-joint torque was measured before and after therapy to assess the time interval before the knee-joint torque decreased to 70% of the initial value. The HPR therapy provided greater increases in muscle endurance and force in prolonged training. Yet the LPR stimulation produced less muscle fatigue compared to the HPR stimulation. The results suggest that HPR is the favored protocol for training, and LPR is better suited for prolonged stimulation.

Adaptive band-pass filter (ABPF) for tremor extraction from inertial sensor data.

Cancelling pathological tremor in everyday living activities may be possible with functional electrical stimulation (FES). One such feasible FES system with feedback from inertial sensors would rely on tremor estimates in real time. We present an adaptive band-pass filter (ABPF) that estimates tremor from volitional hand movement with zero-phase lag. The proposed algorithm is simple and easy to implement. Performance of the ABPF is compared to one popular well-established method for tremor extraction (weighted-frequency Fourier linear combiner, WFLC) using both synthetic data and data from inertial sensors, recorded in tremor patients during "finger to nose" task execution. The results were comparable, favoring ability of ABPF for faster adaptation, higher accuracy and robustness.

Muscle fatigue of quadriceps in paraplegics: comparison between single vs. multi-pad electrode surface stimulation.

We hypothesize that the asynchronous low frequency stimulation of pads within multi-pad electrode will be less fatiguing compared to the conventional stimulation (two single pad electrodes) when generating comparable large forces of paralyzed human muscles. The experiments to verify the hypothesis were conducted on quadriceps of six individuals with chronic spinal cord injury (ASIA score A) who had not participated in any electrical stimulation program. The following stimulation protocols were compared: stimulation with a self adhesive 7 cm x 10 cm Pals Platinum cathode positioned over the top of the quadriceps (f = 40 Hz), and four oval 4 cm x 6 cm cathodes positioned over the proximal upper leg (f = 16 Hz). The anode in both cases was the 7 cm x 10 cm Pals Platinum electrode positioned over the distal part of the quadriceps. We measured the knee joint torque vs. time with a custom made apparatus, and estimated the interval before the knee joint torque decreased to 70% of the maximum. Mean fatigue interval increase for the four-pad stimulation protocol vs. single-pad stimulation protocol was 153.18%. This suggests that the use of multi-pad electrodes is favorable in cases where a prolonged stimulation of muscles is required.