Estimating effective contact and flight times using a sacral-mounted inertial measurement unit

Aurélien Patoz,Thibault Lussiana,Bastiaan Breine,Cyrille Gindre,Davide Malatesta

doi:10.1016/j.jbiomech.2021.110667

Aurélien Patoz, Thibault Lussiana + Show 3 more

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https://doi.org/10.1016/j.jbiomech.2021.110667

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Abstract

Effective ground contact (tce) and flight (tfe) times were proven to be more appropriate to decipher the landing-take-off asymmetry of running than usual ground contact (tc) and flight (tf) times. To measure these effective timings, force plate is the gold standard method (GSM), though not very portable overground. In such situation, alternatives could be to use portable tools such as inertial measurement unit (IMU). Therefore, the purpose of this study was to propose a method that uses the vertical acceleration recorded using a sacral-mounted IMU to estimate tce and tfe and to compare these estimations to those from GSM. Besides, tce and tfe were used to evaluate the landing-take-off asymmetry, which was further compared to GSM. One hundred runners ran at 9, 11, and 13 km/h. Force data (200 Hz) and IMU data (208 Hz) were acquired by an instrumented treadmill and a sacral-mounted IMU, respectively. The comparison between GSM and IMU method depicted root mean square error ≤22 ms (≤14%) for tce and tfe along with small systematic biases (≤20 ms) for each tested speed. These errors are similar to previously published methods that estimated usual tc and tf. The systematic biases on tce and tfe were subtracted before calculating the landing-take-off asymmetry, which permitted to correctly evaluate it at a group level. Therefore, the findings of this study support the use of this method based on vertical acceleration recorded using a sacral-mounted IMU to estimate tce and tfe for level treadmill runs and to evaluate the landing-take-off asymmetry but only after subtraction of systematic biases and at a group level.

Highlights

Back in 1988, Cavagna et al (1988) defined two key running pa rameters denoted as effective ground contact and flight times
The smallest absolute bias was given for 9 km/h, followed by 11 km/h and 13 km/h (Fig. 3 and Table 1). Both effective timings reported a signif icant negative proportional bias at all speeds but were accompanied with small R2 (Table 1). Significant effects for both method of calculation and running speed as well as an interaction effect were depicted by repeated measures ANOVA for tce and tfe (P < 0.001; Table 2)
The most accurate estimation was given at 9 km/h (Fig. 3 and Tables 1 and 2). These findings suggests that the cut-off frequency that estimates best tce and tfe might be speed dependent and reinforce the need to further explore the effect of the cut-off frequency of both gold standard method (GSM) and IMUM, and to explore slower and faster speeds

Summary

Introduction

Back in 1988, Cavagna et al (1988) defined two key running pa rameters denoted as effective ground contact (tce) and flight (tfe) times. They differ from the usual ground contact (tc) and flight (tf ) times by the fact that tce and tfe correspond to the amount of time where the vertical ground reaction force is above and below body weight, respectively, rather than where the foot is in contact with the ground or not (Cavagna et al, 2008a) These effective timings were proven to be more appro priate to decipher the landing-take-off asymmetry of running than the usual timings (i.e., tc and tf ) (Cavagna, 2006; Cavagna et al, 2008a, b). These two parameters are usually obtained from effective foot-strike (eFS) and toe-off (eTO) events, i.e., when vertical ground reaction force goes over and below body weight, respectively. A natural choice is a sacral-mounted IMU, the reason being that such placement approxi mates the location of the center of mass (Napier et al, 2020)

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