Inertial measurement units to estimate drag forces and power output during wheelchair tennis tests.

Introduction:

A way to determine elements of wheelchair mobility performance is the use of inertial measurement units (IMUs) during a match, training or testing situation. Drag forces and power output have, however, never been assessed using IMU technology for wheelchair athletes. The power output of an athlete gives a valid indication of the athletes’ experienced external load, that needs to be produced to maintain a given velocity and which consequently could be compared to the internal load (mechanical efficiency, heart rate, rating of perceived exertion).

One of the key areas identified by wheelchair tennis players is the interaction between tyre pressure and the surface competed on, impacting rolling resistance and thus propulsion and turning effort. Knowledge on rolling resistance is necessary to make a better-informed choice on wheelchair characteristics and understanding its consequences on testing, training, and gameplay in wheelchair tennis.

Study aim: To describe drag force and power loss effects with inertial measurement units in standardised wheelchair tennis coast-down and 10 m sprint tests.

Methods:

Eight highly trained wheelchair tennis players participated in this study using their own competition tennis wheelchair and racket.

All players completed a set of three standardised coast-down trials and two 10 m sprints with different tyre pressures on hardcourt surface. One athlete completed additional tests on a clay/grass tennis-court.

Three inertial measurement units were placed on the individual wheelchair, one on each of the axes of the rear wheels and one on the frame of the wheelchair. This IMU consisted of a gyroscope, accelerometer and magnetometer and allowed measurement of the linear and rotational positions, velocities, and accelerations over time.

Main findings:

Coast down tests

• If the athlete pushes at a constant velocity of 2 m/s, there is a predicted external power loss of 9.6–14.4 W.
• External power losses occurred in approximately 37% of the push cycle for hardcourt, 39% for clay and 36% for grass.
• A higher tyre pressure led to lower drag forces during coast-down tests on hardcourt surface (p = 0.03).

10m Sprint test

• No differences in sprint times, drag forces, power losses and push/recovery times were observed between the different tyre pressures.
• The loss of power is experienced in approximately 35% of the complete pushing cycle.
• During the first five pushes, the push time decreased, while the recovery time, mean and peak power losses per push increased.
• The mean and peak velocities reduced on grass compared to clay and compared to hardcourt.
• For the single athlete, there was an external power loss of 10.4, 15.6 and 49.4 W, respectively, for the hardcourt, clay, and grass. 

Reference:

Rietveld T, Mason BS, Goosey-Tolfrey VL, van der Woude LHV, de Groot S, Vegter RJK. Inertial measurement units to estimate drag forces and power output during standardised wheelchair tennis coast-down and sprint tests. Sports Biomech. 2021 Apr 26:1-19. DOI: 10.1080/14763141.2021.1902555. Epub ahead of print. PMID: 33896385.

Image credit: © Paralympics GB