Abstract
Researchers employ foot-mounted inertial measurement units (IMUs) to estimate the three-dimensional trajectory of the feet as well as a rich array of gait parameters. However, the accuracy of those estimates depends critically on the limitations of the accelerometers and angular velocity gyros embedded in the IMU design. In this study, we reveal the effects of accelerometer range, gyro range, and sampling frequency on gait parameters (e.g., distance traveled, stride length, and stride angle) estimated using the zero-velocity update (ZUPT) method. The novelty and contribution of this work are that it: (1) quantifies these effects at mean speeds commensurate with competitive distance running (up to 6.4 m/s); (2) identifies the root causes of inaccurate foot trajectory estimates obtained from the ZUPT method; and (3) offers important engineering recommendations for selecting accurate IMUs for studying human running. The results demonstrate that the accuracy of the estimated gait parameters generally degrades with increased mean running speed and with decreased accelerometer range, gyro range, and sampling frequency. In particular, the saturation of the accelerometer and/or gyro induced during running for some IMU designs may render those designs highly inaccurate for estimating gait parameters.
Highlights
Studies of running biomechanics suggest that measured kinematic parameters may lead to the insight necessary to improve running performance and reduce injury risk [1,2]
The novelty and contribution of this work are that it: (1) quantifies these effects at mean speeds commensurate with competitive distance running; (2) identifies the root causes of inaccurate foot trajectory estimates obtained from the zero-velocity update (ZUPT) method; and (3) offers important engineering recommendations for selecting accurate inertial measurement units (IMUs) for studying human running
These results show that cumulative distance errors remain below 5% when the percentage of angular velocity data lost due to saturation is below 2.6%, regardless of the gyro range
Summary
Studies of running biomechanics suggest that measured kinematic parameters (e.g., joint angles, stride frequency, stride length) may lead to the insight necessary to improve running performance and reduce injury risk [1,2]. Foot-mounted IMUs provide three-dimensional foot accelerations and angular rotational velocities from which foot trajectories (and associated gait parameters) are derived during walking/running [4,5,6,7,8,9,10]. Doing so requires minimizing the accumulated drift error in the estimated foot velocity and position using the so-called “zero-velocity update” (ZUPT) method [4,5,11]. Prior studies confirm that the ZUPT method yields accurate foot trajectory estimates for walking gait [9,12,13] and running gait with modest speeds (up to 4.36 m/s) [14]. Little research addresses the requirements that ensure accurate trajectory estimates, at faster running speeds, such as those observed in competitive middle- and long-distance running (up to 6.5 m/s) [15,16,17]
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