Pressure Mapping Problems

Comparing Back Pressure Maps

There are three main points to take into account:

(1) Pressure equals Force divided by Surface Area.

(2) All sensors used in pressure mapping systems are compliance sensitive. This means they are responsive to the hardness or softness of the materials between which the sensor mat is placed.

(3) As soon as a horse moves it changes shape.

The consequences of point (1)

The first consideration when comparing back pressure maps is the relationship between force and surface area. For example: if the average pressure has been reduced by one half then the surface area must have doubled (given the same loading, which is the applied force, which is total weight of rider and saddle). If there is not a clear difference in the mapped areas being compared then the pressure reading is in error.

When looking at pressure maps, especially those presented in advertising and press releases it's important not to take what's shown as fact. The questions to ask when looking at an advert or press release claiming great things for a pressure map are:

Is there mention of the rider + saddle weight? (in Kgs or lbs)

Is there mention of the loaded area covered as sometimes non-loaded areas can be included? (square inches or centimeters)

Is there mention of the average pressure? (psi - pounds per square inch or Kgs per square centimeter)

If this information is not given then it's best to doubt the result. I do not think this is deliberate deception it's just that the advertiser or technician carrying out the test does not understand what is being presented.

When the above information is given then the loaded area value can be multiplied by the average pressure value to produce a value close to the rider + saddle weight (keep psi with lbs and square centimeters with Kgs). If the given value for the rider + saddle weight is close to the calculated value (say +/- 10%) then the claims can be relied upon.

The consequences of point (2)

This raises some interesting points. If you take the same horse, rider and saddle and compare the maps when the horse was unfit and fit, there will appear to be an increase in pressure for the same contact area when the horse is fitter. The change is due to the muscle tone difference between the unfit or soft horse (low muscle tone) and harder, fit horse (high muscle tone). A similar result will be noted by putting a wool numnah or soft saddle pad between the horse and the saddle. The soft numnah will appear to have decreased the pressure, but if there is no change in the contact area then the difference is only in the measurement, not in reality.

So, once again, doubt comparations between pressures showing 'improvements' in pressure values between a saddle without and the same saddle with a numnah (saddle pad). Ask the question; did they recalaibrate the measurements for the change of compliance introduced by the material of the numnah. This calibration is easy to do as all that's required is an accurate measure of the rider + saddle weight and loaded area on the horse's back.

It's not only numnahs that introduce different compliance characteristics which may cloud the issue of saddle pressure map comparisons. Different 'flockings' will yield different pressure distributions for the same loaded area as their compliance values will differ. For example: new flocking is much softer than old compressed flocking, the older flocking may give higher values; even the leather used in making the panels will affect the readings. Generally speaking the softer the materials the lower will be the pressure readings for the same rider + saddle weight and loaded area.

The consequences of point (3)

When a horse (just like a human) is standing still the muscle tone decreases and as a consequence the rib cage of the horse drops slightly between the shoulders. For the horse to move at all it must increase its muscle tone (just try moving without increasing your muscle tone) and as tone increases in the serrate muscles the rib cage lifts. As the horse moves from walk to trot to canter there is a constant increase in overall tone with the abdominal muscles tightening and curving the back upwards.

So, a pressure map with the horse standing will be quite different from the horse moving at walk, then change again at trot and again at canter. A saddle fitted exactly to the standing horse is likely to have increased pressure to the front and much less at the back as the horse moves through the gaits. It is a good saddle for standing still in perhaps. A standing 4-point contact may turn to a pressure map with full contact at canter for example. The point I wish to make is that when looking at the pressure maps ask, what was the horse doing when the map was recorded or is this an averaged map over all the gaits (different from an average over an equal time interval over the same ground in all gaits)?

This becomes a very important consideration when pressure maps are compared between different saddles. If the comparative conditions are not stated then doubt the displayed results!

If you ask a saddler to perform saddle pressure mapping on your horse take all three points into consideration and ask for averaged maps for standing still and in all gaits in any saddle you try. Think deeply about what you intend to do in your riding. For example if you hack mainly at walk and trot choose the saddle with best result in these gaits. If you work mainly at canter as in show jumping choose one with the best pressure map for that gait.

Note: the best approach to fitting saddles is to fit to the moving horse and the pressure mapping does help in doing this - trouble is, it is expensive.

The fun way of looking at these saddle pressure maps is that if there is a suggestion that the saddle or pad or rider is defying gravity then someone somewhere has produced an antigravity machine! There'll be more money in that than saddles or saddle pads!

As a final point I do think that once the pressure mapping measurements are fully understood they will be used to good effect in saddle design and horse movement analysis.

You can look at a saddle pressure map for the FnE saddle and think about what's been said.

For more information go to a study by:

de Cocq P, van Weeren PR, Back W.
Saddle pressure measuring: validity, reliability and power to discriminate between different saddle-fits.
Vet J. 2006 Sep;172(2):265-73. Epub 2005 Jul 12

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