Does the Position of Foot-Mounted IMU Sensors Influence the Accuracy of Spatio-Temporal Parameters in Endurance Running?

Abstract

Wearable sensor technology already has a great impact on the endurance running community. Smartwatches and heart rate monitors are heavily used to evaluate runners’ performance and monitor their training progress. Additionally, foot-mounted inertial measurement units (IMUs) have drawn the attention of sport scientists due to the possibility to monitor biomechanically relevant spatio-temporal parameters outside the lab in real-world environments. Researchers developed and investigated algorithms to extract various features using IMU data of different sensor positions on the foot. In this work, we evaluate whether the sensor position of IMUs mounted to running shoes has an impact on the accuracy of different spatio-temporal parameters. We compare both the raw data of the IMUs at different sensor positions as well as the accuracy of six endurance running-related parameters. We contribute a study with 29 subjects wearing running shoes equipped with four IMUs on both the left and the right shoes and a motion capture system as ground truth. The results show that the IMUs measure different raw data depending on their position on the foot and that the accuracy of the spatio-temporal parameters depends on the sensor position. We recommend to integrate IMU sensors in a cavity in the sole of a running shoe under the foot’s arch, because the raw data of this sensor position is best suitable for the reconstruction of the foot trajectory during a stride.

Stride Lengths during Maximal Linear Sprint Acceleration Obtained with Foot-Mounted Inertial Measurement Units

“…Taken together, these findings suggest that, despite our effort to tightly fixate the sensors, the fixation may still have been suboptimal in some cases. The importance of sensor fixation was recently demonstrated by Zrenner et al, who found the lowest errors with IMUs integrated into the sole of a standard type of shoe [ 20 ]. Although we do believe that sensor fixation has affected our results, the extent to which this was the case remains unclear.…”

“…In particular, the high impacts upon touch-down of the feet may introduce an additional challenge for the double integration procedures of acceleration that are commonly used to derive SL. Consequently, only a limited number of studies determined SL with IMUs and did so during running at constant and relatively low speeds (e.g., [ 17 , 18 , 19 , 20 ]). Zrenner et al found that errors in estimated SL increased greatly from 5 to 6 m·s −1 , which, to the best of our knowledge, is the highest speed interval for which IMU-derived SLs have been reported [ 17 ].…”

The placement of foot-mounted IMU sensors does affect the accuracy of spatial parameters during regular walking

“…For calculation, we used a double integration approach similar to [23]. The initial orientation was estimated using a small window of 8 samples (40 ms) centered around at the start of each v min -stride.…”

The placement of foot-mounted IMU sensors does affect the accuracy of spatial parameters during regular walking

“…In our own recent work, we attempted to answer this question for running movements [ 23 ]. We attached eight IMUs to a pair of running shoes at different positions (four sensors per shoe) and collected data from approximately 2400 strides from 24 healthy participants at various running speeds.…”

“…This means that the robustness of systems to these changes must be investigated if we cannot ensure that the sensor is always placed at the same exact position. In particular the quantitative results from [ 22 , 23 ] make it clear that these differences are large enough to affect health and sports applications. Despite the apparent relevance of this topic, position and attachment differences between sensor setups are rarely discussed in literature and no consensus regarding sensor placement exists.…”