The physiological effects of horses’ head and neck positions (HNP) while being ridden is a topic of fierce debate. And until now, there hasn’t been any data on head and neck position’s effect on muscle activity, especially that of the muscles controlling these positions.
Kathrin Kienapfel, MA, a doctoral student at Ruhr-University Bochum, in North Rhine-Westphalia, Germany, recently evaluated electromyography (EMG, a tool that allows researchers to read muscle activity through sensors attached to the skin) activity of three major head and neck muscles when horses performed three characteristic HNPs: free, gathered (competition frame with head high, neck flexed, and nose in front of the vertical), and hyperflexed (with the mouth pointing toward the chest, or behind the vertical). She presented her findings at the 9th Annual International Society for Equitation Science, held July 18-20 at the University of Delaware, in Newark.
The three muscles Kienapfel and colleagues evaluated were the splenius muscles on each side of the neck that attach the neck and upper back vertebrae to the skull; the brachiocephalicus muscles that run from the upper limb to the back of the skull; and the trapezius muscles that attach the neck and mid back vertebrae to the shoulder blade.
In the study they used EMG to measure five healthy Warmbloods’ HNPs in both directions at the walk, trot, and canter, with and without a rider (positions without a rider were achieved using draw reins). Each horse performed, on average, 10 cycles (or 10 steps at each gait) in each position. The researchers compared HNPs between left and right directions, left and right sides of the muscle, with and without a rider, and between gaits. They found that:
- There were no significant differences between ridden and unridden conditions.
- At all gaits, the splenius muscle was significantly less active (e.g., working less) in the hyperflexed position than in the free position; it was most active in the free position.
- At all gaits, the brachiocephalicus muscle was significantly more active in the hyperflexed position than the other positions.
- At the walk, the trapezius muscle was significantly less active in the hyperflexed position than the other positions; its highest activity was during the free position. At the trot, muscle activity in gathered and hyperflexed positions did not differ significantly, and at the canter the muscle showed no differences between any position.
- Only the brachiocephalicus displayed a difference between sides, with the right being more active than the left.
"In HNPs with the nose line in front of the vertical, the topline muscles of the neck (the splenius and trapezius) are activated/trained," Kienapfel summarized. "In contrast, in the hyperflexed position a main muscle of the lower neck (brachiocephalicus) is activated/trained."
She explained that this is important because riders and trainers typically desire a muscular topline in their horses as opposed to a muscular lower neck. "The brachiocephalicus is also a muscle of the foreleg—it swings the leg forward," she said. "In hyperflexion, because of the activation of the brachiocephalicus, you get a more pronounced, unnatural movement of the foreleg.
"These results should be considered by riders and judges as an undesired result of an HNP," Kienapfel concluded.