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Introduction to Equine Gait Analysis

Over the past 20 years, scientific evaluation of the movement patterns of horses has greatly enhanced out knowledge about horses move and how to detect any irregularities. However, until recently, objective evaluation of horse’s gaits would have been restricted to veterinary research institutions due to the cost of the equipment and the complexities of setting everything up correctly. Fortunately, these assessments can now be done in the field (out of the research labs) thanks to the advances in the technology. In fact, we are getting to the exciting point when equine gait analysis is becoming more accessible and affordable for the wider equestrian community.

The most popular tool are inertial measurement units (IMUs) – these are small sensors that can be attached directly to the horse to record data which are then transmitted wirelessly from the sensors to a computer in order to analyse different gait variables.

A horse instrumented with 3 sensors to evaluate upper body movement symmetry of head (poll), withers and pelvis (sacrum).

How can we assess equine movement symmetry?

The most frequently methods of evaluation of the horse’s movement is to look at how symmetrically the horse moves by comparing two halves of the stride (for example during and after the stance of a right limb compared to the left limb). This is usually done in trot as trot is a symmetrical gait so it is easy to compare ‘left and right half’ of the stride. Additionally, in trot the forces acting on the horses body are greater than in walk hence magnifying any irregularities which might be related to pain.

Some might focus on limb parameters (for example protraction/retraction, joint angles) but these have been shown to be highly variable so a lot of the recent research has concentrated on the evaluation of upper body movement symmetry instead. When we refer to upper body we usually look at head (poll), withers and pelvis (sacrum and tuber coxea) and how these markers move during the two halves of the stride. The ‘head nod’ we all look for if we are suspecting forelimb lameness translates into the head being held higher during the stance of the lame forelimb. This has been shown to be related to a reduction in vertical acceleration and, as a consequence, a reduced ground reaction force during the stance phased of the affected forelimb – a compensatory strategy resulting in reduced strain placed on the anatomical structures of the lame limb. Additionally, horses also show reduced upper body movement asymmetry after successful nerve or joint block, i.e. when the pre-existing pain is reduced or abolished (1–3). 

Below are two most frequently used movement symmetry parameters:

  1. The difference in minima – for example for head we are looking if the head nods down equally during the impact of left and right forelimb and similarly for pelvis we look whether the pelvis reaches the same lowest point during the stance of the right and left hindlimb. (In research papers these will be labelled as HDmin (Head Difference in Minima) for head and PDmin for pelvis – this will be an average from a number of strides)
  2. The difference in maxima – here we look at how high the head or pelvis rises after the stance go left and right limb. (In research papers these will be labelled as HDmax for head and PDmax for pelvis)

The difference in minima (Dmin) often relates to weight-bearing problems whereas the difference in maxima (Dmax) often referred to a ‘push-off’ (propulsion) deficit. 

Example of gait analysis output

Here we see reduced push-off (PDmax) and weight-bearing (PDmin) of the left hind limb.

Why we need equine gait analysis?

Evaluation of horse’s movement relies on visual examination which is limited by human capacity for visual perception of asymmetry (4) and temporal resolution of the human eye (5). We are simply not capable of noticing small changes. Additionally, our evaluation is not always 100% reliable. What do we mean by ‘reliable’? First, we can look at intra-rater agreement: If you see the same horse twice, will you give it the same lameness/asymmetry rating? Studies have shown that the same evaluator would not achieve 100% agreement with their own previous evaluation of the same horse (when they were presented with the same videos recording twice at different time points). Secondly, we can look at inter-rater agreement: Do different evaluators agree with each other? Again, this is never 100% – in fact it can be as low as 40% depending on the type (forelimb/hindlimb) and severity of lameness.

On the other hand, equine gait analysis can detect very small asymmetries with high sensitivity and has high repeatability between trials (6). This can be particularly useful for tracking changes over time – for example to evaluate our training plans or to track progress of rehabilitation. Measuring movement patterns objectively is important because it allows us to quantify what is happening and helps us decide what works and what does not. This, in turn, allows us to evaluate and, if necessary, improve existing training or rehabilitation methods  and consequently maximise equine welfare. 


Would you like to learn more about horse movement asymmetries and practical applications of gait analysis? You can now buy a recording of my recent webinar: ‘Asymmetrical or Lame? Where do we draw the line?’

Would you like to have your horse evaluated with a state of the art equine gait analysis system? The assessment is carried out at your own yard and the findings will be explained to you on the day plus a detailed report will be emailed to you so that you can keep track of any changes over time.


References:

1 Maliye et al. (2013) An inertial sensor-based system can objectively assess diagnostic anaesthesia of the equine foot. Equine Veterinary Journal
2 Keegan et al. (1997) Effects of anesthesia of the palmar digital nerves on kinematic gait analysis in horses with and without navicular disease. American Journal of Veterinary Research
3 Pfau et al. (2014) Identifying optimal parameters for quantification of changes in pelvic movement symmetry as a response to diagnostic analgesia in the hindlimbs of horses. Equine Veterinary Journal
4 Parkes et al. (2009) Evidence of the development of ‘domain-restricted’ expertise in the recognition of asymmetric motion characteristics of hindlimb lameness in the horse. Equine Veterinary Journal
5 Holcombe (2009) Seeing slow and seeing fast: two limits on perception. Trends in Cognitive Sciences 
6 Keegan et al. (2011) Assessment of repeatability of a wireless, inertial sensor-based lameness evaluation system for horses. Am J Vet Res

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