Inertial sensors for assessment of back movement in horses during locomotion over ground

Abstract

SummaryReasons for performing study: Assessing back movement is an important part of clinical examination in the horse and objective assessment tools allow for evaluating success of treatment. Objectives: Accuracy and consistency of inertial sensor measurements for quantification of back movement and movement symmetry during over ground locomotion were assessed; sensor measurements were compared to optical motion capture (mocap) and consistency of measurements focusing on movement symmetry was measured. Methods: Six nonlame horses were trotted in hand with synchronised mocap and inertial sensor data collection (landmarks: T6, T10, T13, L1 and S3). Inertial sensor data were processed using published methods and symmetry of dorsoventral displacement was assessed based on energy ratio, a Fourier based symmetry measure. Limits of agreement were calculated and visualised to compare mocap and sensor data. Consistency of sensor measurements was assessed using Pearson correlation coefficients and linear regression to investigate the effect of speed on movement symmetry. Results: Dorsoventral and mediolateral sensor displacement was observed to lie within Ϯ 4-5 mm (Ϯ 2 s.d., 9-28% of movement amplitude) and energy ratio to lie within Ϯ 0.03 of mocap data. High levels of correlation were found between strides and trials (0.86-1.0) for each horse and each sensor and variability of symmetry was lowest for T13 followed by T10, T6, L1 and S3 with no significant effect of speed at T6, T10 and T13. Conclusions: Inertial sensor displacement and symmetry data showed acceptable accuracy and good levels of consistency for back movement. The small mediolateral movement amplitude means that changes of <25% in mediolateral amplitude (also unlikely to be detected by visual assessment) may go undetected. New sensor generations with improved sensor sensitivity and ease of use of equipment indicate good potential for use in a field situation.

Ambulatory Assessment of Instantaneous Velocity during Walking Using Inertial Sensor Measurements

“…For cyclical motions such as bipedal locomotion, the instantaneous velocity can be modeled by the sum of the 3D cyclical component of velocity and the velocity of forward motion averaged over each cycle, henceforth called the Average Progression Velocity (APV) [7,8]. It is commonplace to estimate the 3D cyclical component of velocity by numerical single time-integration of the linear acceleration, followed by high-pass filtering [8,9]. Recently, a Fourier-based method was proposed for analytical double time-integration of the linear acceleration of points on the human body moving cyclically [10]; this method, for which implementation one pelvis IMU and an additional IMU attached to one shank (shank IMU) were suggested, performed better than existing methods as for the closeness of agreement between the 3D displacements estimated by the pelvis IMU and the OMCS reference.…”

Is a standalone inertial measurement unit accurate and precise enough for quantification of movement symmetry in the horse?

“…Custom written software (MATLAB, Natick, US) was used to process data from both types of IMUs following published procedures (Pfau et al, 2005, Warner et al, 2010: calibrated acceleration data were rotated into a horse based reference frame based on sensor orientation and knowledge about orientation of the sensor mounting.…”

“…The sternum has been used previously (Barrey et al, 1994) and body orientation seems better suited than head orientation. In multi-sensor systems with synchronized sensors (Warner et al, 2010, Starke et al, 2012a,c, Pfau et al, 2012, the sacral sensor can be used to segment all sensor data (Starke et al, 2012b). If thoracic limb hoof contact is required, IMUs located on the distal limb (Olsen et al, 2012) or hoof mounted accelerometers or gyroscopes (Witte et al, 2004, Keegan et al 2005 provide precise results.…”

“…Ideally, the two IMUs should be used in both locations at random, however to keep statistical analysis simple the sensors were placed in consistent locations (in the sagittal plane) for all horses. In support of this decision, Warner (et al, 2010) Both IMU types were fixed with the same attachment method: cross-elastic adhesive foam fixative (Animal Polster, Snogg, Norway) to the horse and double sided tape between this and the IMU. The IMUs hence record the movement of the skin rather than the movement of the underlying bony landmark.…”

“…Bias and limits of agreement (Bland and Altman, 1986) were established with respect to a validated system based on multiple synchronized 6-DoF IMUs (MTx, Xsens, The Netherlands, Pfau et al, 2005, 2007, Warner et al, 2010, Starke et al, 2012a, 2012c). …”