Freewheels project: technological performance, the key to accessing sports competition!
© Inria / Photo C. Morel
On 8 October, Jérôme Parent will be taking part in a rather special sports competition: the Cybathlon.
The goal for this sporty forty-year-old, who has been paraplegic for over 20 years, is to cover 750 metres on a bike powered by his legs thanks to electrical stimulation.
It is the result of almost a year of hard work and difficult technical choices.
For several months now, the Freewheels project team has been refining its technical and sports strategy prior to the Cybathlon competition. The aim of this painstaking work: to enable Jérôme Parent and his bike to become one. And to do this, Christine Azevedo and Benoît Sijobert, from the CAMIN research team at the Inria Sophia Antipolis - Méditerranée centre and the LIRMM (Laboratory of Computer Science, Robotics, and Microelectronics (Montpellier)), were not starting from scratch. Indeed, their research team develops electrical stimulation equipment to help people with motor impairments (hemiplegia, Parkinson's disease, medullar injury...). The CAMIN team researchers have been working for several years with Dr. Charles Fattal, head of department at CRF DIVIO, the functional re-education centre in Dijon, but up until now they had never focussed on cycling.
A constant adaptation of the tools
"BerkelBike is one of the few companies to offer functional electrically-assisted bikes. A new, programmable stimulator is currently being developed, and they are interested in our expertise in the field of automation. That is why we entered into a partnership " Christine Azevedo explains. "This company proposes high-end products, mainly aimed at re-education. For Freewheels, we preferred to adapt an electrical stimulation system to a less expensive tricycle. So we decided to adapt the BerkelBike electrical stimulator to a commercially-available three-wheeled recumbent bike whose boom, wheel height and pedalling mode were adjusted specifically for Jérôme. The bike, which is designed for able-bodied people, had to meet several criteria - both on a technical and ergonomic level. The tricycle was selected for its ease of transfer from a wheelchair via retractable handles, with a position that would prevent the risk of a fall or sores and also limit rolling resistance (smooth tyres with flexible casing and lightweight aluminium frame) as much as possible ." In particular, the Freewheels project team chose to transform the free wheel into a fixed gear: the bike stops as soon as the pedals stop turning. This enables the use of the inertial force of the wheels in order to help Jérôme Parent to operate the pedals and get through any stops that are difficult to overcome using only the quadriceps and hamstring muscles.
Developing a stimulation template
The stimulation programme was then adapted: the aim is that Jérôme Parent's muscle tire as little as possible over the entire race, so that they are resistant enough to keep going for 750 m. The chosen solution divides the stimulation into six channels. "We can only carry out external stimulation on the muscles, which prevents us from stimulating all of the muscles involved in pedalling by an able-bodied person. Moreover, Jérôme's glutes cannot be used, which is an additional constraint
", Christine Azevedo explains. Two stimulation channels will be placed on each group of quadriceps in order to prevent the early onset of fatigue and spread the load over different muscles, and another channel will activate the hamstrings. A sensor captures the position of the pedal mechanism and sends the information to the stimulator. Depending on the stimulation template that has been programmed, the different muscle groups are stimulated in order to trigger their contraction at a certain pedalling angle. It took months to refine this stimulation model, in order to obtain the most fluid movement possible without excessively tiring the cyclist's legs. The first assessment criterion was the feedback from Jérôme: "During the training sessions, I informed the team if there was a problem with my pedalling. I sometimes had abnormal sensations, as if I was tipping over backwards, or I saw that my movements were jerky: so we modified the templates one day at a time
Several sensors were integrated in order to monitor the pilot's performance more quantitatively, via software created especially for the Freewheels project by Benoît Sijobert as part of his thesis. Inertial units (HIKOB, an Inria start-up), a cardiac monitoring belt (ANT+ technology) and force pedals (Powertap) made it possible to monitor the rhythm, speed, distance and pedalling angle obtained during training. Originally, the stimulator parameters were intended for real-time modulation, but the time constraints before the competition meant that the technological development required in order to integrate this data into the control loop was not possible. Apart from the activation template linked to the angle of the pedal mechanism, electrical stimulation is defined by three main parameters: the intensity of the current, the duration of the impulsions and their frequency. Jérôme can modify the first parameter whilst pedalling in order to maintain effective muscle contractions despite the gradual onset of fatigue; the other parameters are set in advance.
For almost a year Dr. Fattal, helped by the physiotherapist Anne Daubigney, prepared Jérôme's muscles for stimulation. During all of the training sessions, the pilot's heart rate and blood pressure and the maximum time before tiredness set in were recorded. "We observed a significant improvement in endurance, he can now last a full seven minutes ", the doctor explains. "We thought of Jérôme not as a patient, but as a full member of the team, and his remarks are very important in order for us to progress ", says Christine Azevedo. "He is also responsible for understanding how to be in the best possible condition on the starting line: "I think that, on the day of the competition, I will need quite a short warm-up, just enough to get my muscles to the right temperature ", Jérôme concludes. Following the competition, tests will make it possible to determine if bone density has increased and if the composition of Jérôme Parent's muscles has "evolved favourably." "The aim of the Freewheels project goes beyond the competition , Charles Fattal explains. We want to enable other paraplegics or tetraplegics to use these types of tools. Once, thanks to Jérôme, the proof of concept and feasibility have been established, we will be able to work with a greater number of patients ."
The main difficulty for all of the team will have been preparing for a competition. Jérôme Parent will need to give his best at a precise moment. He will not have the opportunity to start over again. "It is a major change to our usual habits: within the context of our experiments the patient can be tired one day, so he comes back another time to start again and it doesn't really matter. In this specific case, we need to perfectly understand how Jérôme reacts and which training programme is best adapted to him ", Christine Azevedo explains. Her team has also sought to adopt the most robust solution possible, so that it can, without fail, be operational on the big day; the "choices have sometimes been difficult because they ran counter to our desire for technical and scientific refinement in order to ensure operationality in the context of a race ."
Christine Azevedo concludes
Taking part, all together, in the Cybathlon is the reward for months of preparation and work - we believe that our team has met the challenge it set out to take on, regardless of the result of this race.
One last imponderable
The last imponderable concerns the floor covering, on the day of the competition. Depending on its degree of resistance, Jérôme will require more or less force in order to pedal. The entire team will only have access to it 45 minutes prior to the start of the race.