Anatomy of a Saddle

English saddles are built on a somewhat rigid tree (Figure 27-1) that distributes the rider’s weight over a large area of the horse’s back. However, the inherent rigidity of the tree can cause localized pressure points if it is not correctly fitted to the individual horse. The arch, also known as the gullet plate or head plate, supports the pommel, and the points extend downward from the arch to stabilize the front of the saddle across the withers. The angle of divergence of the points should match the outward slope of the horse’s shoulders, and the points should be long enough to stabilize the front of the saddle (Figure 27-2; see Figure 27-1). The bars are the support mechanism for the stirrup leathers, and the cantle underlies the seat.

The tree gives attachment to the leather exterior, which varies greatly in shape and size depending on horse and rider morphology and the sport they participate in. Dressage saddles typically have a straight front edge of the flaps to accommodate the relatively extended hip angle and vertical thigh of the dressage rider (Figure 27-3). Jumping saddles have a more rounded flap to accommodate the flexed hip angle and forward position of the rider’s knee for jumping. The panels, which are attached to the underside of the saddle (see Figure 27-3), provide large and symmetric weight-bearing surfaces over the epaxial musculature on each side of the horse’s back. The left and right panels are separated on the midline by a gullet that should be high and wide enough to ensure that there is no direct pressure on the vertebral spinous processes (see Figure 27-3).

The availability of electronic pressure mats has provided information about the force on the horse’s back and the pressure distribution patterns in each gait. In walking and trotting, which are symmetric gaits, force and pressure are similar on the left and right sides of the horse’s back. In the walk, a graph of total force reveals small oscillations around the weight of the rider plus saddle weight (Figure 27-4) with six peaks and troughs per stride. Maximal force during walking is only slightly greater than the rider plus saddle weight. In trot, the total force shows two large oscillations per stride, with the horse’s back being unloaded in the suspension phases when the rider is projected upward and unloads the saddle and maximally loaded during the diagonal stance phases when the rider descends into the saddle. The maximal force is approximately double the weight of the rider plus saddle, and it is applied twice per stride. In the canter, the total force has a single large oscillation in each stride, with the horse’s back being unweighted in the suspension phase and maximally weighted in the middle of the stance phase. The maximal force at the canter is two and a half to three times the weight of the rider plus saddle and is applied once per stride. Thus the force on the horse’s back is considerably higher at the trot and the canter than at the walk, and the weight of the rider determines both the maximal force on the horse’s back and the amount of extension of the intervertebral joints. The pressure distribution, which can be measured using an electronic pressure mat (see Color Plate 27-1), also changes in a characteristic cyclic fashion during each gait, and evaluation of pressure scans may be helpful in localizing high-pressure areas (see Color Plate 27-1).