How rider biomechanics affects the horse
By Jennifer O. Bryant
Reprinted from June 2017 issue of USDF Connection
World-renowned researcher Dr. Hilary Clayton is known for her groundbreaking findings in the areas of equine biomechanics. We don’t tend to think of her as focusing on the rider, but that’s exactly what she did at her session on “Rider Posture and Mechanics” at the 2016 Adequan/USDF Annual Convention in St. Louis.
As dressage riders, we know that we use our bodies to influence our horses. What we don’t necessarily know is how, or how much. In her session, Dr. Clayton deconstructed some fundamental rider-biomechanics findings and offered some research-based explanations of how, exactly, skilled riders use their bodies differently than novices.
Your Effects on Your Horse
You give aids; your horse responds. But what’s actually happening in the process?
The rider has various effects on the horse, according to Dr. Clayton. One kind is the type we tend to think about in dressage, which is known as behavioral effects. These are the muscular responses in the horse’s body that we train him to produce when he feels our leg, seat, and weight aids.
But the rider’s body actually produces other, profound effects on the horse’s body, according to Dr. Clayton. The rider’s mass, or the way that mass is distributed in the saddle, has inertial effects: It produces changes in the horse’s movements or energy expenditure. The more weight the horse is carrying, the higher his heart rate and the greater his body’s production of lactic acid, which is a byproduct of exercise. Greater weight carried also increases the duration of the horse’s stance phase, which is the period of time in any gait that one or more limbs is in contact with the ground— not desirable in dressage, as longer stance phases make the gaits look more grounded and less “floating.”
You don’t have to be a larger person to affect your horse, however. “Carrying an unpredictable rider— one whose movements are not well controlled and synchronized with the horse’s movement—disturbs the horse’s balance and uses more energy,” Dr. Clayton said.
In other words, good riding isn’t just about presenting a nice picture or doing well in competition; it’s actually better for your horse’s body. Which leads us to the topic of equitation. What is “good riding position,” and how does it help our horses?
“Correct rider alignment is good posture. Good posture minimizes effort, maximizes shock absorption, and facilitates the correct application of the aids,” Dr. Clayton said.
Key to good posture is correct spinal alignment.
“A human baby doesn’t have spinal curvature,” Dr. Clayton said. “The curves develop as the muscles strengthen and the baby is able to support its head and neck. The thoracic (upper back) curves develop first, and the lumbar (lower back) curve comes later as the lower body strengthens.”
The ideal posture is what’s known as neutral spine—with your natural spinal curves aligning such that you stand balanced from head to feet. Try Dr. Clayton’s method of determining your own neutral-spine position: Stand with your back against a wall, heels a couple of inches in front of the wall. Stand with your chin level and your nose pointing straight forward, and with the back of your head, the backs of your shoulders, and your buttocks touching the wall. “You should be pretty close to neutral spine,” she says.
However, some spinal abnormalities, such as lordosis (a hollow back or “swayback”) and kyphosis (“humpback”), can make achieving neutral spine challenging or impossible, said Dr. Clayton.
Knowingly or unknowingly, the rider can exaggerate or minimize a horse’s mild lameness, said Dr. Clayton. On a sound horse, the sitting trot weights both diagonals equally. But the rising trot weights the “sitting” diagonal more than the rising one—meaning that, depending on which diagonal the rider chooses to post, a mildly lame horse may appear either more sound (if the rider sits on the lame diagonal) or less sound (if the rider sits on the sound limb) than he actually is.
Because of the inherent uneven weighting in the rising trot, it’s important to change diagonals frequently, Dr. Clayton said.
The horse has the most freedom of movement when the rider’s seat is not in the saddle at all. Two-point or “halfseat” position, with the rider standing slightly in the stirrups, increases the rider’s stability in terms of movements of the center of gravity, and also evens out the effects of the rider’s weight on the horse’s back over the course of the stride. It is a useful riding position, especially for young horses or for giving the horse a break from the driving or collecting seat, Dr. Clayton said.
One “rider problem” may actually be the result of lameness. A study showed that saddle slip can be associated with hind-limb lameness. The uneven movement behind displaces both the saddle and the rider off to one side.
Considering the extensive body of equine-biomechanics research, and the time and effort (not to mention money) riders invest in improving their skills, it is surprising that “the [equestrian] industry is lacking a large and more comprehensive study of riders,” Dr. Clayton said. She summarized the findings of the modest studies that have been conducted.
In one study of 12 riders, subjects were asked to sit on a flat surface with equal weight on both seat bones. But using a pressure mat, the researchers discovered that in fact most of the riders weighted their left seat bones more heavily than the right. Ten of the 12 riders showed more outward rotation of their right hips as compared to their left. The subjects’ handedness was not noted.
“Generally, a right-handed person’s left leg is stronger and more stable,” Dr. Clayton noted. “The right leg is more mobile and dexterous.”
Another study looked at the torso movements of 17 female riders, all right-handed, in the walk, trot, and canter. In the walk, trot, and left-lead canter, the riders’ right shoulders moved more than their left shoulders. In the right-lead canter, both shoulders moved an equal amount—and the riders’ right legs were longer than their left legs.
Achieving Better Posture in the Saddle
Correct riding position starts, literally, with your pelvis, which Dr. Clayton calls “the rider’s direct connection to the horse.”
When you sit in the saddle, the contact points are your two seat bones. The rider’s pubic bone “is not normally in contact with the saddle,” Dr. Clayton said.
When dressage instructors talk about “using the seat,” they’re referring to the rider’s ability to control the angle and movement of the pelvis in order to influence the horse. You can use your core muscles to rotate your pelvis backward (posterior pelvic tilt) or forward (anterior tilt). (The rotation is indicated by the direction the top of the pelvis moves.)
“An anterior pelvic tilt hollows the rider’s back and slides the seat bones backward, which is not an effective position for riding dressage,” Dr. Clayton said. “A hollow back, with its tight lumbar and hip-flexor muscles, is associated with rider tension. The rider’s chin may jut forward. This position is often seen in disciplines such as saddle seat and hunter seat, but it is not effective for dressage because we can’t influence the horse properly.”
A “following seat” in dressage is in more of a neutral-spine alignment. As horse and rider move up the levels, the rider begins to spend more time in a posterior pelvic tilt, which Dr. Clayton called “the collecting seat.” The rider engages her lower abdominal muscles and her gluteal and hamstring muscles, and her seat bones “glide to the front of the saddle.” The pelvis is tilted backward, allowing the rider to actively influence the horse, and “in collection there is posterior pelvic tilt throughout the stride. The center of pressure under the saddle moves closer to the withers, and the loaded area on the horse’s back decreases,” she said.
The amount of upward pressure exerted on the rider varies throughout the horse’s stride, Dr. Clayton said. The pressure is highest after the middle of the diagonal stance phase: “The horse pushes himself and the rider upward into the next suspension; then, as the horse starts to descend, the rider actually unloads the saddle.”
A rider’s core strength is important not only for pelvic control, but also for spinal stabilization. “You must stabilize your spine before moving any other part of your body,” Dr. Clayton said.
A dramatic example of the core at work is the biomechanics of riding a half-pass, in which the horse trots or canters on a diagonal line while bent in the direction of travel.
“In the half-pass, your core holds your body over the horse’s inside shoulder. You actually pull the horse in the desired direction,” she said, “instead of ‘pushing him over’ as some dressage texts describe.”
Coordinating for Harmony and Influence
We aspire to ride in harmony with our horses, and “harmony between horse and rider” is actually a collective mark in the US Equestrian rider tests. Biomechanically speaking, what is harmony?
As Dr. Clayton defines it, harmony happens when the movements of the horse and the rider are so closely synchronized that the rider appears to be “just sitting there” doing nothing while the horse performs of his own accord.
Easier said than done, of course. And some researchers have studied how, exactly, skilled riders do it.
The easiest gait to ride in terms of coordinating one’s movement with the horse is the canter, Dr. Clayton said. The most difficult: no, not the trot! It’s actually the walk, in which studies show the rider’s movements are the least well-coordinated with the horse’s. Why, we’re not yet sure. “My theory is that it’s from the rider trying to push the horse into a bigger walk by wiggling the pelvis back and forth,” she said. “If the rider limits the forward pelvic tilt and sits more still, the coordination improves.”
Novice and expert riders vary significantly in their ability to coordinate their movements with their mounts’. In the sitting trot, expert riders synchronize their pelvic and trunk movements with their horses; they also sit more upright (novices tend to lean forward), carry their heads upright with less nodding, and show less opening and closing of their elbow and knee angles, Dr. Clayton said.
In the canter, expert riders show an equal degree of sideways trunk “roll” on both leads. They also have less trunk movement than novices, Dr. Clayton said.
“An expert rider synchronizes her upper-body and arm movements with the vertical motion of the horse’s back during each stride,” Dr. Clayton said. “Novices will be in sync in the suspension phase, when horse and rider are highest, but not in the middle of the diagonal stance, when the elbows and wrists move further downward than the torso before starting the next ascent. The rider needs to maintain sufficient positive muscle tension through the shoulders and arms so the entire upper body moves as one unit.”
The most skilled riders have the ability not just to coordinate with their horses, but actually to influence their rhythms and tempos.
“An expert rider coordinates her movements with the horse, adapts to and controls its movement patterns, and makes the gaits more consistent and stable,” Dr. Clayton said. Horses ridden by skilled riders show more consistent rhythms and tempos than those ridden by novices—but even a less-skilled rider can improve the consistency of the horse’s movement.
Finally, a poor-fitting saddle will at least partially negate the influence of a skilled rider. Horses ridden in properly fitted saddles move more consistently than those whose saddles do not fit, Dr. Clayton said, because the horse in an ill-fitting saddle is constantly changing his movement pattern to seek a position that makes the saddle feel more comfortable.