Why inertial sensors and not just video?

Q: New artificial intelligence based apps for mobile/cellphones are available for assessing movement asymmetry. Why would I bother instrumenting a horse with sensors?

A: A great question, and the answer to this will have to be reviewed constantly over the coming years as continuing progress is neing made in both inertial sensor technology and processing as well as in artificial intelligence for markerless tracking of humans and animals.

For now (January 2023), inertial sensor based systems are (still) the more versatile tools. In particular our EquiGait systems provide the following advantages:

1) more complex movements can be measured:

For example, our standard setup is able to measure withers movement in addition to head and pelvis movement. This allows us to draw direct conclusions about whether a measured movement asymmetry is related to force asymmetries between the forelimbs or between the hind limbs.

As a second example, our 6 or 9-sensor wireless systems or our 4-sensor DOT system measure 6-dimensional movements of the back. This is still very difficult to achieve from a single-camera setup due to possible occlusions (the back not easily visible from in front of the horse or from behind) and since multi-dimensional quantification (more than 2 dimensions) is not without challenges from a single camera view. Attaching a sensor to the horse overcomes these challenges.
Why do these more complex movements matter?
Horses and other four-legged animals compensate for deficits affecting one limb by off-loading weight onto one or several of the remaining limbs. It has been shown that withers movement allows to detect whether a movement adaptation, for example increased or decreased head movement, is related to a problem with one of the front limbs or with one of the hind limbs.

Similar to humans, movement restrictions are not located to the limbs. When we adapt our movement, other body parts, most importantly the back, are affected too. Our EquiGait systems are able to analyze back movement. This provides unequalled analytical power for poor performance examinations as well as for tracking progress during treatment or rehabilitation regimens!         

2) straight-line and lunge and ridden:

similar to the challenges with quantifying multi-dimensional back movement from a single camera, it is more challenging to analyze video data where the viewing angle (between the camera and the horse) is constantly changing. Think lunge or ridden exercise as an example. For now, inertial sensors, mounted on the horse and hence with the measurement reference system moving with the horse, have advantages for this application. Yes, lunge analysis is possible from video, but think about the multi-dimensional changes that are happening during circular movement: the horse may lean (more or less) into the circle. This affects movement planes other than vertical movement. Our inertial sensors measure with six degrees of freedom: they assess translations: vertical, but also sideways and forward-backward. They also measure back movement such as flexion-extension, lateral bending and axial rotation. 

3) measure the unseen:

Oftentimes, subtle movement deficits maybe felt while you are riding your horse. If you want to measure subtle changes affecting the horse in this situation, including the movement of the back, optical systems, including expensive 3D motion capture systems based on multiple cameras will struggle to provide measurements of all regions of interest, in particular what is going on with the back of the horse under the saddle. 
Inertial sensors are providing measurement solutions for many different applications: in-hand, on the lunge, ridden. They provide a detailed quantification of complex movement patterns going beyond vertical movement symmetry patterns such as head nod and hip hike and provide a comprehensive multi-dimensional assessment of functionally relevant parameters that matter for health and performance of horses.  

4) anywhere, anytime:

Data analysis is made on your device (Windows laptop/tablet) and does not require internet access) as some other cloud based artificial intelligence tools may need. Results are available in seconds (wireless systems) or reliably (without internet access!) a couple minutes after the measured exercise (DOT system). Other systems that depend on 'cloud computing' may experience variable delays depending on network availability and speed.

5) trade-off between instrumentation time versus analysis time.

Of course putting sensors on horses takes up a little bit of time. In our experience, the more often you do this the better and faster you get. Putting 3 sensors (our minimum setup) on the horse will take in the order of 2 minutes. Once the sensors are on the horse you can perform as many measurements (within battery-life, 5 to 6 hours) as you want and the analysis will be done in seconds, every time! A great benefit during complex lameness exams! No waiting for data upload or analysis!
Trust your palpation skills: put the sensors where you know they need to go! 

6) no ongoing subscription fees.

Our systems do not require signing up to a monthly or case-based subscription system as typically encountered for cloud-based services. The system is yours (once you have purchased it!). 

7) no privacy concerns.

Inertial sensors do NOT provide a video assessment of the horses in your care. They simply measure the movement of strategic anatomical locations on the horse. This means you do not need to worry about (cloud-) storage of large video files, potentially revealing identifying information about horse or owner. Nobody stops you from taking videos of interesting cases and storing them alongside the sensor gait analysis results in your practice management software.       

Q: is there any sense in using both: inertial sensor and video/AI based analysis?

A: Absolutely! Combine more complex analysis enabled by our EquiGait systems with long-term assessment over a period of time through smartphone-based measurements.  

As outlined above, we believe there are still a number of essential advantages using our multi-sensor approaches, in particular when it comes to assessing more complex interactions between multiple landmarks (head, withers, pelvis) or more complex 6-dimensional patterns of back movement. However, what is wrong with establishing the 'normal pattern' of head and pelvic movement of your horse? Or how about measuring your horse's movement in conjunction with changes to your training regimen or over a period of rehabilitation?

Our EquiGait systems provide you with state-of-the-art insights into more complex patterns and exercises!

Please download our leaflet here with a comparison table providing an overview of advantages and disadvantages of different gait analysis modalities as we at EquiGait see them!    

For more information please email: info@equigait.co.uk