Ergometer testing
Contents
Ergometer testing#
This guide will explain how the settings of the Esseda wheelchair ergometer can be used to simulate overground propulsion or set a target power output for your participants. It assumes a properly operated and calibrated system.
The Esseda is a wheelchair roller ergometer developed and produced by Lode BV (Groningen, The Netherlands). It is equipped with a set of servomotors and load cells to simulate and measure wheelchair propulsion. With the servomotors in the ergometer you can make propulsion as light or as heavy as you would like it to be.
A simple mechanical model is used to simulate overground propulsion. This model simulates:
The inertia of the participant + the wheelchair
The rolling resistance of the wheelchair
Both values can be changed accordingly in LEM. Weight can only be set before every measurement. Friction can be changed during measurements to allow for ramp or step protocols. Total friction (left + right module) is calculated by multiplying the weight of the participant and the wheelchair (m) with the gravitational constant (g) and a rolling resistance constant (μ):
Setting power output#
Oftentimes researchers are more interested in power output (W). During steady-state propulsion, the velocity of the wheelchair oscillates around a steady point with every push. Additionally, simulated friction is assumed to be independent of velocity. As such, power output can be assumed to be the product of the frictional force (F) and mean velocity (v):
As such, the expected power output on the Esseda wheelchair ergometer can be calculated with relative ease.
Calibrations#
The Esseda wheelchair ergometer needs to be calibrated before testing. The system friction of the ergometer is determined using a dynamic calibration procedure. Every calibration is unique due to the differences of each participant (mass, distribution, tension straps). The dynamic calibration procedure starts at 0 m/s and steadily increases in small steps to 2.5 m/s. Although every calibration procedure is unique for the wheelchair-user combination, all calibrations follow a similar pattern.
Noise#
The measurement signal of the Esseda wheelchair ergometer is subject to a certain noise level. Tension on the straps, wheelchair tyre type and changes in posture can all add noise to the signal. Butterworth filters can be used on the force and velocity signal to filter some noise.
Acceleration#
The use of servomotors in the ergometer leads to a realistic acceleration and deceleration of the wheelchair-user combination dependent on the friction coefficient provided. Differentiating the velocity signal results in the acceleration signal. The measured forces are also dependent on the acceleration of the wheelchair-user combination.
Measurement modes#
The Esseda wheelchair ergometer is able to use four different modes to evaluate wheelchair propulsion performance.
Isoinertial#
In the isoinertial mode, the rolling resistance coefficient can be set and the wheelchair user can be tested under realistic conditions. The rolling resistance coefficient can be adjusted to simulate different surfaces or gradually increase the intensity of wheelchair propulsion.
Isokinetic#
In the isokinetic mode, a speed limit can be set on the ergometer. It will feel like a ceiling effect. Participants can push as hard as they can, they will not be able to go beyond the given speed limit. The servomotor of the ergometer adjusts the friction based on the velocity.
Isospeed#
In the iso speed mode, the wheels can spin at a given velocity. The velocity is not affected by the applied forces, which could be used to increase coordination issues in wheelchair propulsion.
Isometric#
In the isometric mode, the rollers of the wheelchair ergometer are blocked. This allows the wheelchair-user to complete an isometric strength test. The wheels can be pushed as a hard as someone can without them moving.
References#
De Klerk, R., Vegter, R. J. K., Veeger, H. E. J., & Van der Woude, L. H. V. (2020). Technical note: A novel servo-driven dual-roller handrim wheelchair ergometer. IEEE Transactions on Neural Systems and Rehabilitation Engineering, 28(4), 953–960. https://doi.org/10.1109/TNSRE.2020. 2965281
Janssen R.J.F., Vegter R.J.K., Houdijk H., Van der Woude L.H.V., de Groot S. Evaluation of a standardized test protocol to measure wheelchair-specific anaerobic and aerobic exercise capacity in healthy novices on an instrumented roller ergometer. PLoS One. 2022 Sep 6;17(9):e0274255. https://doi.org/10.1371/journal.pone.0274255