Nuchal Ligament – Role in locomotion

The nuchal ligament is made of very elastic tissue, which means when it is stretched it stores ‘strain energy’. When this strain is released movement occurs due to the energy stored, the beauty of this energy is it requires very little effort. Due to the neck of the horse being very long and heavy the nuchal ligament plays a very important role in lifting the head, especially from a grazing position to upright, which is vital for a prey animal to be able to do quickly (read more about the anatomy here).

From a riding perspective you can see that the position of the neck will change the strain not only on the nuchal ligament but also the supraspinous ligament, which effects several areas of the body such as the sternum and spine as you can see in the image below.

(Image from Denoix and Pallioux in Willem & Clayton Equine Locomotion)

In one study (Nestadt et al. 2015) dimensions of the nuchal ligament (the lamellae and funicular cord) were measured in relation to different head and neck position in the cadaver foal, I have made an adapted figure of some of the head and neck positions from this paper.

To briefly summarise, it found that different positions change how the nuchal ligament stretches (which you may be able to see in the picture I have drawn). In a more flexed position such as behind the vertical and in extreme elevation the nuchal ligament was slack in the caudal (lower) portions and had a greater increase in length in the dorsal portion (greater stretching over the poll), this proposed that in these positions there was less support of the cervical spines in the caudal neck (now relate that back to my post about lamellar attachments) and potentially greater strain over the poll. In a correct ‘on the bit’ position there was little change in the nuchal ligament dimensions compared to neutral, meaning the nuchal ligament could function normally along with muscle recruitment to support the head and neck. In a long and low position (head in front of the vertical) even stretching of all the lamellar bands was shown, this was thought to support the neck structures via the elasticity of the nuchal ligament, therefore allowing the muscles to relax.

On a side note, when the neck bends laterally it will also rotate, in some horses you may notice a flick of the mane to one side when the neck is bent laterally, this may be due to a lack of attachment of the NL on the spinous processes of C2. I do question if there is a lack of attachment that there is a greater amount of rotation/instability of the poll and therefore a greater need to ensure the surrounding muscles are functioning in a healthy way to support the head and neck.