Estimation of Ground Contact Time with Inertial Sensors from the Upper Arm and the Upper Back

Abstract

Ground contact time (GCT) is one of the most relevant factors when assessing running performance in sports practice. In recent years, inertial measurement units (IMUs) have been widely used to automatically evaluate GCT, since they can be used in field conditions and are friendly and easy to wear devices. In this paper we describe the results of a systematic search, using the Web of Science, to assess what reliable options are available to GCT estimation using inertial sensors. Our analysis reveals that estimation of GCT from the upper body (upper back and upper arm) has rarely been addressed. Proper estimation of GCT from these locations could permit an extension of the analysis of running performance to the public, where users, especially vocational runners, usually wear pockets that are ideal to hold sensing devices fitted with inertial sensors (or even using their own cell phones for that purpose). Therefore, in the second part of the paper, an experimental study is described. Six subjects, both amateur and semi-elite runners, were recruited for the experiments, and ran on a treadmill at different paces to estimate GCT from inertial sensors placed at the foot (for validation purposes), the upper arm, and upper back. Initial and final foot contact events were identified in these signals to estimate the GCT per step, and compared to times estimated from an optical MOCAP (Optitrack), used as the ground truth. We found an average error in GCT estimation of 0.01 s in absolute value using the foot and the upper back IMU, and of 0.05 s using the upper arm IMU. Limits of agreement (LoA, 1.96 times the standard deviation) were [−0.01 s, 0.04 s], [−0.04 s, 0.02 s], and [0.0 s, 0.1 s] using the sensors on the foot, the upper back, and the upper arm, respectively.

The Validity of a Three-Dimensional Motion Capture System and the Garmin Running Dynamics Pod in Connection with an Assessment of Ground Contact Time While Running in Place

“…To avoid a potential signal bias due to filtering, we were required to choose this higher threshold, which is the same as that also utilised in numerous other investigations involving a force plate [ 6 , 25 , 26 ].…”

“…Since this sensor’s data are collected through a watch, it can be used anywhere [ 24 ]. Recently, Gonzales and colleagues [ 25 ] reviewed several investigations that were designed to validate IMU sensors [ 12 , 26 , 27 , 28 , 29 , 30 , 31 ], in two of which [ 27 , 29 ], the sensor was mounted on the subject’s pelvis. The validation of the IMU with an instrumented treadmill provided estimates of the accuracy and precision of GCT measurements that were −29 ms and 20 ms, respectively [ 27 ].…”