No abstract
SUMMARY Biomechanical studies often employ optical motion capture systems for the determination of the position of an object in a room-based coordinate system. This is not ideal for many types of study in locomotion since only a few strides may be collected per `trial', and outdoor experiments are difficult with some systems. Here, we report and evaluate a novel approach that enables the user to determine linear displacements of a proprietary orientation sensor during cyclical movement. This makes experiments outside the constraints of the laboratory possible, for example to measure mechanical energy fluctuations of the centre of mass during over-ground locomotion. Commercial orientation sensors based on inertial sensing are small and lightweight and provide a theoretical framework for determining position from acceleration. In practice,the integration process is difficult to implement because of integration errors, integration constants and the necessity to determine the orientation of the measured accelerations. Here, by working within the constraints of cyclical movements, we report and evaluate a method for determining orientation and relative position using a modified version of a commercial inertial orientation sensor that combines accelerometers, gyroscopes and magnetometers, thus giving a full set of movement parameters (displacement,velocity and acceleration in three dimensions). The 35 g sensor was attached over the spine of a horse exercising on a treadmill. During canter locomotion(9.0 m s-1), the amplitudes of trunk movement in the x(craniocaudal), y (mediolateral) and z (dorsoventral)directions were 99.6, 57.9 and 140.2 mm, respectively. Comparing sensor displacement values with optical motion capture values for individual strides,the sensor had a median error (25th, 75th percentile) in the x, y and z directions of 0.1 (–9.7, +10.8), –3.8(–15.5, +13.7) and –0.1 (–6.3, +7.1) mm, respectively. High-pass filtering of the displacement data effectively separated non-cyclical from cyclical components of the movement and reduced the interquartile ranges of the errors considerably to (–3.6, 6.2),(–4.0, 3.8) and (–4.5, 5.1) for x, y and z displacement, respectively, during canter locomotion. This corresponds to (–3.2, 5.5)%, (–6.7, 6.3)% and (–3.3, 3.7)%of the range of motion.
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.
SUMMARY Although a large number of foot-fall sequences are possible in quadrupeds,few sequences are routinely used. The aim of this paper is to characterise, by foot-fall pattern, the gaits used by horses and develop a novel technique to classify symmetric and asymmetric gaits using one common criterion. To achieve this speed and relative foot-fall, timings of all four limbs of eight Icelandic horses were measured using accelerometers. Linear discriminant analysis (LDA) was performed to find criteria that are optimal for discriminating between the different gaits. This also allowed us to evaluate whether gaits should be considered a continuum or as discrete entities. Foot-fall timings (stance times, swing times, duty factors and stride frequencies) for walk, tolt, trot, pace, left canter, right canter, left gallop and right gallop during over-ground locomotion at a range of speeds are presented. In the gaits of walk, tolt, trot and pace, foot-fall timings were equal between left and right hindlimbs and forelimbs so these gaits can be considered as symmetrical. Differences in stance times and duty factors were observed between gaits but are unlikely to be of biological significance due to their similar magnitude and inconsistent relative trends. This implies that metabolics or peak limb forces derived from contact times are unlikely to be the principal driving factors in gait transition between walk, trot, pace,canters and gallops, although these factors may influence the use of tolt at the lower and higher speeds. Gaits did cluster in the LDA space and the running gaits (tolt, trot, pace, left and right canters and gallops) could be considered a kinematic continuum but the relative relationship with walk may be more complex. Thus, LDA analysis has enabled common criteria to be discovered to accurately classify equine gaits on the basis of foot-fall timings on a stride-by-stride basis.
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