From Theory to practice: monitoring mechanical power output during wheelchair field and court sports using inertial measurement units

An important performance determinant in wheelchair sports is the power exchanged between the athlete-wheelchair combination and the environment, in short, mechanical power. To monitor the mechanical power during wheelchair sports practice, inertial measurement units (IMUs) might be used. However, a well-founded and unambiguous theoretical framework that follows the dynamics of manual wheelchair propulsion is required to validly apply IMUs for mechanical power assessment in wheelchair sports. Such a framework does not yet exist. Therefore, this research has two goals. First, to present a theoretical framework that supports the use of IMUs to estimate power output via power balance equations. Second, to create a set of guidelines on how to use IMUs to monitor mechanical power during wheelchair propulsion supported by experimental data. After verifying the theoretical framework, an IMU model was defined. Subsequently, the validity of the IMU model and underlying assumptions was determined. Therefore, power was estimated from IMU data during wheelchair propulsion and was subsequently compared to gold standard optical motion capture data. Data was collected from eleven participants without wheelchair experience propelled an all-court sports wheelchair on a large treadmill. At the same time, kinematics were measured using two IMUs and an optical motion capture system. The results reveal that, with a proper drag or deceleration test, one IMU on the wheelchair frame and one IMU on the wheel axis, decent power estimations can be obtained in daily wheelchair (sports) practice. To conclude, the theoretical framework and the resulting IMU-based power is thus well suitable to estimate mechanical power during straight-line wheelchair propulsion in wheelchair court sports and daily wheelchair practice, and it is an important first step towards feasible power estimations in all wheelchair (sports) situations.