How your body protection works

As described above foams use the structure around the air pockets to absorb the energy, but with air bladders it is the air movement and pressurisation that does the work. Air is relatively inefficient compared to foams, but by using large volumes, often 4 inches thick, the absorption happens over a longer time resulting in much less force to the body. To be effective, the air cushions need to be pre-pressurised and have a large impact area that results in a large increase in pressure. (If you ever have manually pumped up a bicycle tyre, you know how much more effort is required to increase the pressure and stiffness of the tyre increases.)

If you land on a shape that can penetrate through the 4 inches of the tube e.g. a fence rail or post, then the air cushion will provide much less protection than foam.

Much is made of inflation speed, which is important as it takes a fraction of a second from leaving the horse before impacting the ground or obstacle. But for air cushions to be effective, they need a certain level of pre-pressurisation and so the most important question is the time that it takes before the air cushions become effective. The Satra M38 specification does exactly that measurement. This is much more appropriate that using high speed video to measure inflation speed as there is no measurement of the pressure in the tube.

A technique often used by designers to increase inflation speed is to reduce the size of the tubes. The less the volume to fill, the quicker the inflation speed, but this reduces the energy absorption capability of the system.

To maintain precise control of the position of the air cushions, a robust structure is required. This can be either by having a girth strap that pushes the air cushions against the body. This requires that the air jacket is worn loose to create space for the air cushions to expand. This results in the chest being punched upon inflation and maybe a fight between the body protector and the air jacket as they may not be aligned due to the loose fit prior to inflation. If the air jacket is poorly adjusted, then this can result in severely restricted breathing and a delay in CPR being applied.
Some air systems are designed to inflate outwards and can be worn closely fitted to the body. Not only does this eliminate the discomfort upon inflation, it allows easy removal in the event that CPR is required.

Brain motion can be exaggerated if the neck can move excessively during an accident. Research has shown that females have weaker necks than males and can result in more head injuries. Motor racing uses the Hans system, but an air jacket that locks onto the jaw can reduce head motion significantly. Allowing the rider to tuck & roll is an important protective technique, so forward movement of the head is necessary to allow this. However, forcing the head into a forward position can result in neck injury, so your air jacket should never contact the back of your helmet. Obviously having a well-fitting air jacket is essential to reduce this possibility.

Many riders complain of injury to their pelvis and having protection in this area with foam is impractical, but this is an area that air can perform very well.