Optimising Performance in Paraplegic FES-Cycling by Modulating Stimulation Parameters
Aksöz, Anil E.
- Doctoral Thesis
Rights / licenseIn Copyright - Non-Commercial Use Permitted
Recumbent cycling exercise achieved by functional electrical stimulation (FES) of the paralysed leg muscles is effective for cardiopulmonary and musculoskeletal conditioning after spinal cord injury, but the limitations of this technology prevent its' full potential to be realised. In order to address the limitations of FES cycling (low mechanical output and low endurance due to early onset of muscle fatigue), the overall aim was formulated as follows: "the aim of the project is to optimise performance during stimulated cycling exercise in people with spinal cord injury by systematically modulating stimulation parameters and assessing new stimulation strategies to maximise power output and endurance." By achieving this aim, will make human-powered mobile cycling a more realistic recreational option. A series of experimental studies were carried out using a custom-made, precision-instrumented dynamometer which was developed especially within and for this project. The dynamometer was used for tests involving healthy able-bodied (AB) subjects. The dynamometer studies with AB subjects focused on two possible methods of optimising the efficacy of stimulation of the quadriceps muscle group: using stochastically-modulated pulse patterns (i.e.\ random variation of inter-pulse interval) and combined randomisation of stimulation parameters (i.e.\ pulse-width and amplitude). The stochastic modulation approach was also tested using a precision-instrumented FES-cycling testbed. In the first experimental series with AB subjects, only the inter-pulse interval (IPI) was modulated. In the second test series, both IPI and pulse duration were changed according to a statistical distribution. Mobile implementation of new stimulation strategies were tested on the custom-made recumbent FES tricycle during the FES bike race at the Cybathlon in Zurich. The studies with the custom-made dynamometer showed that stimulation strategies that use randomised modulation of IPI can improve the ability of functional electrical stimulation applications to perform repetitive, non-isometric contractions with significantly higher power output in short term tasks. In the study with the FES-cycling test-bed, power output during the first and last 30 seconds of stimulation with randomised IPI showed no differences compared to stimulation with constant IPIs. But constant frequency stimulation showed significantly higher overall power output compared to stochastically modulated IPI. This result was unexpected, since previous measurements with the same protocol on a knee dynamometer demonstrated higher power output for randomised IPI. Compared to the dynamometer, where only knee-extensors were stimulated (i.e. quadriceps), the hamstrings were also stimulated on the FES-cycling ergometer system. This more complex motion makes it more difficult to stimulate accurately. The overall power output values might have been negatively impacted by ineffective stimulation of the hamstrings. In another study, it was observed that combined randomisation of the stimulation amplitude and pulse-width significantly increased the fatigue resistance during the tests with the knee dynamometer and with the FES-test bed. Randomisation of stimulation parameters has a direct effect on muscle fibre recruitment and when used systematically, higher power output and higher fatigue resistance can be achieved. %Conclusion With the help of the new stimulation strategies studied, performance optimisation of stimulated cycling exercise can be realised and the limitations of this technology can be addressed by maximising power output and endurance. Contributions of this work have significant potential to make human powered mobile cycling a more realistic recreational option Show more
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ContributorsExaminer: Riener, Robert
Examiner: Hunt, Kenneth J.
SubjectFunctional electrical stimulation; Neuromuscular electrical stimulation; spinal cord injury (SCI); Interpulse interval; Fes cycling
Organisational unit03654 - Riener, Robert / Riener, Robert
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