Controlling and reporting power output is essential for all wheelchair propulsion research. These measurement techniques allow for the measurement and estimation of power output which we can then apply to overground wheelchair propulsion but also for measurements on the treadmill or on the ergometer. Wheelchair propulsion is a straining activity with a high risk of shoulder injury and inactivity which is why we need proper research techniques.
These methods are not only for daily wheelchair propulsion but can also be used for wheelchair sports or during rehabilitation. Demonstrating the procedures will be Marika Leving, one of the post-docs in our team, and Rick de Klerk, one of the PhDs. To perform a coast down test, have the participant sit in an active position as standardized as possible with the feet on the foot rest, hands on the lap, and looking straight ahead.
The positioning of the participant in the wheelchair is crucial and should be reflective of the position during measurements. To record the deceleration data using IMUs, attach one IMU to each wheel hub and one to the center of the chair under the seat. Write down which IMU is attached where and in what orientation for later reference and use the NextGen IMU Synchronized Network Manager executable to turn on and connect the IMUs.
To collect the time and velocity data, open the tools tab, select data logger, and click start. Then briefly accelerate the wheelchair to a high velocity and immediately let the wheelchair decelerate to a complete standstill without interference while recording the time and velocity data. After the last analysis, open the coast down test software on the computer and set the participant weight.
Select import data to import the coast down data file. Use the slider to select the coast down sections in the data, clicking grab selection after each data selection. When all of the data has been selected, click calculate outcomes and note the mean rolling friction and rolling friction coefficient.
To perform a drag test, at least 30 minutes before the measurement, turn on the treadmill power supply and set up the drag test computer and force sensor. In the drag test computer software, click power table measurements and ensure the participant is on the treadmill in the standardized active position. To measure the offset of the load cell, first record the force with no rope attached.
At the end of the measurement, click OK.Connect the wheelchair to the force transducer with a lightweight rope ensuring that the load cell and rope are horizontally aligned with the rear wheel axle of the wheelchair. Accelerate the belt to the desired speed and increase the inclination of the treadmill. When the position of the treadmill and wheelchair user combination is stable, record the force and angle.
Then use the angle and force to fit a linear regression equation and click accept and OK to calculate the force at the zero angle of the treadmill. To set the power outlet, subtract the drag test friction from the target friction to calculate the required pulley weight and position the pulley in front of or behind the treadmill making sure that the pulley is centered. Attach the pulley to the wheelchair and make sure that the rope is level.
Inform the participant that the weight in the pulley might move the wheelchair and use a basket of known low mass and a carabiner to attach a zero to one kilogram weight to the pulley system. Then slowly increase the weight as necessary until the desired power output is achieved. For external power output during the ergometer-based testing, turn on the ergometer at least 30 minutes before testing and open the associated software on the computer.
Click the participant widget and add and assign the participant an ID.Enter the body weight of the participant and click OK.Click the wheelchair icon, enter the wheelchair specifications and click OK.Click the protocol widget. To create a custom protocol, select add and custom protocol and click next. Assign the protocol an appropriate name and click create.
To set the resistance to the friction coefficient obtained from the coast down test, select stages and click add stage and resistance. Set the resistance coefficient to 0.01, the target speed of the participant to four kilometers per hour, and the use fixed duration to 16 and click OK.To set up the participant screen, remove all of the widgets from the screen and click add widget. Then select the wheelchair direction widget and drag the widget into the main window.
Use the alignment system to align the wheelchair on the rollers and use the four-belt system to fasten the wheelchair. Check that the wheels are not touching the ergometer and are properly aligned and position the participant in the standardized active position. To calibrate the ergometer in the associated software, click the crosshairs icon and press start calibration.
To estimate the internal power output during handrim wheelchair propulsion, turn on the spirometer at least 45 minutes before any calibrations or testing. Use the associated software to calibrate the spirometer according to the factory guidelines. Place the spirometer mask on the participant.
Adjust the elastic bands on the head cap to create a tight seal around the face and secure the spirometer hose so that it does not interfere with the movement. Then press the test icon to begin the analysis. Select new subject on the display of the spirometer.
For submaximal exercise testing, select the breath-by-breath mode. To start recording, press the record key. In this analysis, the relative and absolute difference distributions between coast down friction and measured power output during overground, treadmill, and ergometer wheelchair propulsion are determined with an overall lower power output calculated for overground propulsion.
Bland-Altman analysis for coast down friction and measured power output during overground, treadmill, and ergometer wheelchair propulsion confirmed these findings. Please remember that the estimated power output is only valid for the position that the participant was in during the calibration and is highly dependent on the surface. After this procedure, we can use precision registration and measurement wheels to calculate the forces on the shoulder.
Because of these techniques, we are now capable of monitoring and standardizing power output which makes collaboration easier. The subject should not wear loose or dangling clothes during any of the tests.
