As you know, sometime I look in Jean Luc work picking up paragraphs that I think are interesting. This is part of a study that is going to be part of our IHTC’s January installment. It is a very interesting study analyzing from the kinematics of the hind and front legs all the way to the work of the back and upper neck muscles, how the horse’s body deals with the lowering of the neck and consequent increased load on the forelegs. 

This is the silhouette of a horse working long and low. This is not an exaggeration. This is the exact copy of a picture extracted from a video promoting the lowering of the neck. The author sees a horse reaching with the neck and swinging the back. This opinion is far removed from reality. If we analyze the horse locomotor mechanism from the alighting hind leg to the muscles involve in the lowering of the neck, we see a totally different picture. In fact a very damaging picture will surface. We start here with the kinematics of the alighting hind leg.

The horse is at the trot going into the fly period before landing on the right diagonal, (left hind leg and right foreleg). The left front leg is still carrying a lot of weight, which is not surprising considering the orientation of the horse’s body. The horse is heavily on the forehand and consequently the horse has to adapt the kinematics of the hind and front legs to such imbalance on the forelegs. For comparison, we place the picture of a horse working at a normal balance.

At this sequence of the stride, unless damaged by inappropriate training technique, the left foreleg should be off the ground and into the swing phase. Under normal circumstances, the forelegs produce more upward vertical force than the hind legs. The forelegs produce 57% of the vertical impulse while the hind legs produce only 43%. The horse picture on this silhouette carries too much weight on the front legs to be able to properly use the upward propulsive activity of the forelegs. The kinematic adaptation to excessive weight is inducing abnormal stresses on the whole front limb structure from the bones and joints to the soft tissues.  We will analyze later in this discussion, the kinematics abnormalities of the forelegs and their consequent damages on the joints, tendons and ligaments.

 Considering the forward movement of the body and the position of the left hind leg shortly before impact, one can objectively conclude that the impact of the left hind leg will occur only slightly ahead of the vertical of the stifle, which is no engagement at all. Without any constraint, a horse engages naturally the hind legs more forward than the horse working with a low neck posture. (On the IHTC document, this sequence is demonstrated with a horse working at the lunge line with a low neck posture. The video commences at exactly the same sequence and frame by frame, shows where the hind leg touches the ground).

Due to this early impact, the supporting hind legs is not going to be capable to decelerate the horse’s body during the first half of the stance. From impact and until 45% of the support phase, which is referred to as the stance, the supporting hind leg decelerates the horse’s body resisting gravity and inertia forces. This sequence of the stride is named the braking phase. A better terminology is “decelerating” phase. During this decelerating phase, the joints and associated muscles and ligaments absorb as well as resist gravity and inertia forces, accumulating elastic strain energy that is immediately used in the following pushing and swing phase. Balance control is created increasing the duration of the time the supporting hind leg remains on the ground. “It should be borne in mind that the weight of the rider will raise two- or three-fold during locomotion and also that more energy is required by a mounted horse and this energy must be obtained by increasing the stance phase so as to recover more energy during the swing.” (J. L. Morales, DVM, PhD, 1998) 

On the silhouette of the horse working with a low neck posture, the alighting of the hind leg occurs too far back altering the horse’s capacity to resist attraction of gravity and inertia force and therefore, the hind leg capacity to control balance during the decelerating phase. The kinematics of the alighting hind leg also handicaps the horse ability to store elastic strain energy for the following swing phase.

Early impact of the hind leg creates the situation of a functional straight hock, which induces the same stresses on the hock joint than a morphologic straight hock. According to James Rooney such kinematics abnormality induces stress on the hock joint between Mt3 and T3. “This shortened stride causes a functional straightleg and arthrosis of Mt3-T3.

And the study goes on all the way to the neck. The first sentence about the neck is an interesting fact. Lower neck muscles don’t have the strength to elongate the upper neck muscles. For a great part, the lowering of the neck is created by gravity. The head and neck weight 10% of the horse’s body weight and the work of the upper neck muscles is to resist attraction of gravity that is pulling the neck down to the ground. As the neck lowers, he upper neck muscles do not reach or stretch but instead resist attraction of gravity. Jean Luc Cornille