Collection : a biomechanical approach part 1

The scientific point of view supplements the numerous equestrian treatises, and objectifies their descriptions. Master horsemen describe, the consequences  and causes of collection in the horse in their theories, and then draw up riding methods. These descriptions are based on perceptions and visual observations. Due to the limitations of the human eye, or of the brain’s interpretation of what we see, it became desirable to bring in measurement.

J,Marey (1830-1904) was the first to carry out measurements on the horse’s locomotion. He developed recording devices, which according to him, solved the dual problems of faithfully analysing actions which our senses cannot perceive accurately, and clearly expressing the results of the said analysis. The horse was equipped with exploratory horseshoes (figure 1) on soft ground, or with pneumatic sensors placed on the canons on hard ground. The main problem with these measurements was the transmission of the data which was performed with techniques such as styluses, drums and air tubes (figure 1).

Figure 1 : Exploratory horseshoe (J.Marey, 1873) consisiting in a rubber ball maintained by means of a part fitted to the shoe. When the ball is compressed, the air escapes through the tube, which is linked up to a recording device held by the rider.

This method enabled him, for each of the horse’s gaits, to estalish the order in which the feet stike the ground, the time each hoof is on the ground, the length of the stride (figure 2). He also developed the photographic gun which enabled him to take 12 photographs of a moving being with one lens. Then he discovered, thanks to a photographic method, the parabolic path taken by an articulated body’s center of gravity. Similar experiments conducted by G. Demeny on man, make the two of them pioneers in the concepts of mechanical movement analysis.

At around the same period, Muybridge used several lenses to decompose the fast gaits. His studies provided very extensive support for scientists (figure 3) and artists.

Research into the horse’s locomotion became very extensive in the 1970s. The measuring equipment used became more sophisticated and the quality of the measurements made improved. Studies into the dressage horse, and based on scientific measurements, are mainly kinetic. Numerous studies by an American team (H. Clayton & al) and a Swedish team (Holstöm & al) concerning the dressage horse’s locomotion, also described from accelerometer sensor recordings taken during training, and in competition (Barrey, Biau). In this fact sheet the results from the different scientific studies have been compiled to objectively understand the definition of collection in Equestrian text books.

« Collection is the attitude of a balanced horse, ...  

A body is balanced when the vertical projection of its center of gravity is maintained within the base of support (support polygone).

...ready to move its body mass in any direction, and able to work alternately on long or  short bases ».

Let us summarize the first part of the definition : Collection is an attitude which favours movement. From a biomechanical point of view favouring movement means :

• Creating movement from a halt, whatever the direction or the force, or
• Altering a movement (slowing down, changing direction,etc).

Body movement is created or altered by forces produced around the center of gravity.

What is therefore the best attitude to produce the forces in any direction around the center of gravity ?

There is a precise moment for both man and horse, where an optimal attitude is sought after so as to manage both trajectory and speed. Three performance criteria are taken into consideration to find the best compromise : speed, the angle of takeoff and the height of the center of gravity.

Bunching-up is an attitude which is characterised by a lowering of the center of gravity enabling to gain in mobility in terms of speed and trajectory management.

Movement is created by muscle contractions (figure 6) which close the angles between joints, produce internal forces in the joints, which in turn alters ground reaction forces. The latter causes a change in the center of gravity. This force varies constantly. It is often referred to in the field as « weight, weight transfer, moving weight back etc »...

These forces have been measured in collected gaits (Clayton, 1994,1997 ; Biau, 2002 Weishaupt, 2009). These studies brought to light the elevator role of the front limbs, and  driving role of the hind limbs at a collected trot, whereas in piaffe there is less activity with a braking role of the hind limbs (figure 8). In a collected canter (Merkens, 1993; Deuel & Park, 1990; Clayton, 1994), the driving force of the hind limb decreases and is approximately equivalent to the combined weight of horse and rider, with direction playing a determining part, the diagonally opposite front limb is the driving limb, with a thrust force which increases (1,5 x weight) (figure 9). 

What are the consequences of these forces on the locomotor parameters ?

At a trot, the authors (Clayton, 1997; Holmström, 1995 ; Biau, 2002) described a longer support phase in collected gaits of competition horses, going as far as an absence of flight phase in piaffe, as well as desynchronisation of the trot diagonal (hindlimb striking the ground 30ms before the forelimb), this is the opposite in piaffe, with the forelimb striking the ground before the hindlimb. The authors also describe a decrease in tempo end length of stride in collected trot, which is contrary to the FEI rules description, which recommends maintaining tempo. The difficulty in maintaining tempo is less marked for canter.

Collection is an attitude which is characterised by a lowering of the center of gravity so as to obtain better mobility in terms of management of trajectory and speed. This scientific approach highlights the concept of COMPROMISE in managing the height of the center of gravity, trajectory and speed… Ground reaction forces induced by the muscle contractions involved, have consequences on the collected gaits, mainly in a decrease in tempo, and an increase in the support phase of the limbs.

See the next part of this article in : Collection : a biomechanical approach : part 2.