Simultaneous Gait Analysis with Inertial Sensors and Treadmill

Spatiotemporal gait data were collected simultaneously using the portable gait analysis system RehaGait® (Hasomed GmbH, Magdeburg, Germany) and an instrumented treadmill (Zebris FDM-T, Zebris medical GmbH, Isny, Germany). The RehaGait® system consists of two mobile inertial sensors (dimensions: 60 × 15 × 35 mm) and analysis software [19 (link)] and is a new version of the previously published RehaWatch® [18 (link)]. Each sensor comprises a 3-axis accelerometer (±16 g), a 3- axis gyroscope (±2000 °/s) and a 3-axis compass (±1.3 Gs). The sensors were attached to the lateral aspect of each shoe (Fig. 1) using special straps to measure linear acceleration, angular velocity and the magnetic field of the foot at a sampling rate of 500 Hz. Manufacturer proprietary software was used to obtain temporal and spatial gait characteristics.Fig. 1

Photograph showing the senor placement on the lateral aspect of subjects’ personal shoes

The instrumented treadmill consists of a treadmill ergometer with an integrated pressure sensor mat comprising a matrix of high-quality capacitive force sensors (range, 1–120 N/cm²; precision, 1–120 N/cm² ± 5 %) and analysis software. The walking surface of the treadmill (length: 1.5 m; width: 0.5 m) comprises 5378 force sensors. The system measures the dynamic pressure distribution under the feet while walking on the treadmill at a sampling rate of 120 Hz. Spatiotemporal gait characteristics were computed automatically from the pressure data within the software. According to the manufacturer, heel-strike is the time of initial contact (threshold, 1 N/cm²) and toe-off the last frame before all sensor pressure values for the foot of interest drop below the threshold. Stride length is calculated as the distance between two initial heel pressure points of alternate sides. Stride time is defined as the time between two consecutive heel-strikes of the same foot and cadence as the number of steps per minute. In addition, the treadmill speed set on the tachometer was recorded. We used the tachometer speed as reference value for the validity analysis and speed calculated from the pressure data for the reliability analysis.