FES-Cycling at the Cybathlon 2024: assessing accuracy of power-pedals for low power output in a virtual race scenario

The Cybathlon is a unique international competition platform for evaluating assistive technologies under real-life conditions. In the most recent edition, the FES-Cycling discipline was conducted on stationary smart trainers (Wahoo Kickr) within a virtual race environment. Participants could use either the smart trainer or a pedal-based power meter as the primary power source. As both systems were not specifically designed for the very low power outputs typically generated during FES-Cycling, the outcomes of the competition require careful interpretation.

This work summarizes the FES-Cycling competition at the Cybathlon 2024 and evaluates the accuracy of pedal-based power meters used in the virtual race. Race performance data from ten pilots representing eight international teams were analyzed. Pedal-based power measurements were compared against a validated smart trainer during the competition. In addition, an assessment in a controlled environment was conducted to quantify pedal accuracy in the low-power range (< 25 W) using a crank-based power meter as reference. The influence of pedal mounting torque, ankle-orthosis mounting position, and crank-length compensation was systematically investigated.

Four of the ten pilots completed the full virtual race distance of 1960 m within the 8-min time limit. Mean cycling speeds (7.8-19.5 km/h) exceeded those reported for the over-ground Cybathlon 2016 race. Analysis of valid race segments revealed substantial overestimation of pedal-based power relative to the smart trainer, with relative errors ranging from 14.7 to 66.6%. Additional accuracy measurements confirmed that pedal-based power was sensitive to mounting torque and particularly to ankle-orthosis position, with lateral displacement of the foot causing pronounced overestimation. Crank-length compensation reduced systematic bias, but residual errors and increased variability persisted at higher cadences.

Commercially available pedal-based power meters and stationary smart trainers are currently not well suited for reliable performance assessment in low-power FES-Cycling competitions within virtual race environments. While virtual formats offer clear logistical advantages, engaging training opportunities and rich performance data, traditional race formats should be reconsidered to better align with the functional goals of FES-Cycling. Future competitions should prioritize over-ground cycling, assessing externally observable outcomes such as distance and time, which may further enhance pilot motivation and public visibility.