Four-limb wireless IMU sensor system for automatic gait detection in canines

Abstract

This study aims to develop a 4-limb canine gait analysis system using wireless inertial measurement units (IMUs). 3D printed sensor holders were designed to ensure quick and consistent sensor mounting. Signal analysis algorithms were developed to automatically determine the timing of swing start and end in a stride. To evaluate the accuracy of the new system, a synchronized study was conducted in which stride parameters in four dogs were measured simultaneously using the 4-limb IMU system and a pressure-sensor based walkway gait system. The results showed that stride parameters measured in both systems were highly correlated. Bland-Altman analyses revealed a nominal mean measurement bias between the two systems in both forelimbs and hindlimbs. Overall, the disagreement between the two systems was less than 10% of the mean value in over 92% of the data points acquired from forelimbs. The same performance was observed in hindlimbs except for one parameter due to small mean values. We demonstrated that this 4-limb system could successfully visualize the overall gait types and identify rapid gait changes in dogs. This method provides an effective, low-cost tool for gait studies in veterinary applications or in translational studies using dog models of neuromuscular diseases.

Figure 1

Illustration of sensor mounting and sensor/laboratory testing coordinates. (a) 3D-printed IMU sensor holder; (b) IMU sensors in holders with attached cushion and Velcro strap; (c) Mounting positions on the forelimb and hindlimb; (d) A dog with 4-limb sensors mounted; (e) Four IMU sensors placed in a synchronization board for heading direction synchronization.

Figure 2

Representative IMU signals (3-axis accelerometer readings Ax, Ay, and Az and 3-axis gyroscope readings Rz, Ry, and Rz) acquired from a forelimb and a hindlimb of a dog. Vertical dashed lines mark the center of the Rz peak, and horizontal dashed lines indicate the width of the Rz peak.

Figure 3

Examples of IMU signal markers (Table 1) used to detect the time points of swing start and end events in forelimb (a–d) and hindlimb (e–h). The black vertical dashed lines indicate the search window boundaries, whereas the star symbols indicate the location of the swing start marker (SSM, black/red star) and swing end marker (SEM, green star). W1 and W2 indicate the search windows for swing start and swing end, respectively.

Figure 4

Pearson’s correlation of the four gait parameters (Eq. (1)) obtained from the IMU (vertical axes) and GAIT4Dog (horizontal axes) systems in the synchronized validation study. The correlation coefficient r and p values are given in each pairwise plot. SWD, swing duration; STD, stance duration; SDS, stride duration based on swing start; SDE, stride duration based on swing end.

Figure 5

Bland and Altman plots of the four gait parameters (SWD, STD, SDS, SDE) to study the agreement between IMU (with subscript IMU) and GAIT4Dog (with subscript G4D) measurements in the synchronized validation study. The horizontal axes are the arithmetic mean of IMU and G4D readings, and the vertical axes are their difference. The measurement unit is second in all axes. The dashed lines are the mean bias between the two systems. The solid lines indicate the 95% confidence interval of the agreement. SWD, swing duration; STD, stance duration; SDS, stride duration based on swing start; SDE, stride duration based on swing end.

Figure 6

An example of time-resolved gait type detection using the 4-limb IMU system. The solid-color boxes in the top panel indicate the swing phase of a limb. The white space between two solid-color boxes indicates the stance phase (on-ground paw). In the lower panel, the pawprint in light gray represents off-ground paws, and the pawprint in solid colors represents on-ground paws. LH: left hindlimb, LF: left forelimb, RF: right forelimb, RH: right hindlimb.