The research of Hilary Clayton: From bit studies to Olympic performance

In my previous blog I told you a bit about myself and how I got to where I am today. This time I’ll tell you about some of the areas of research I’ve been involved in. The McPhail Equine Performance Centre was built at Michigan State University to accommodate my research - it represented a new generation of buildings incorporating research and clinical evaluations of sport horses under the same roof. It housed equipment for 3D analysis of kinematics and ground reaction forces as well as a saddle pressure mapping system. Often, though, the tools we needed for research weren’t available commercially and we’d have to cobble together our own equipment. What would we have done without duct tape and baling twine?

Dr. Hilary Clayton, blog author

 

Veterinarian, researcher, and horsewoman Dr. Hilary Clayton, BVMS, PhD, Dipl. ACVSMR, FRCVS is a legend. For over 40 years, she’s carried out research in the areas of locomotor biomechanics, lameness, rehabilitation, conditioning programs for equine athletes, and the interaction between rider, tack, and horse. A lifelong rider, she’s also competed in many equestrian sports. We are excited to announce that she will be sharing her expertise through a series of blogs for Sleip.

Bit studies using fluoroscopy

At Glasgow University I initiated a series of fluoroscopic studies investigating the position and action of various bits in the horse’s mouth. Fluoroscopy provided real-time moving Xray images of the bit inside the horse’s mouth in a way that had never been seen before. About 20 years later these studies were revived and continued in Michigan with the help of Jane Manfredi, a visiting student from the Atlantic Veterinary College. As an aside, Dr. Manfredi was recently appointed as the third MaryAnne McPhail Dressage Chair in Equine Sports Medicine and I look forward to her future contributions to sport horse science. 

Getting back to the bit studies, here are some of the things we learned: 

• When a bit is in the horse’s mouth, it lies on top of, and partly surrounded by the tongue
• The tongue covers the bars of the mouth and cushions the action of the bit
• Most horses prefer a narrow mouthpiece over a fat one due to space restrictions inside the mouth
• Horses prefer to have the bit high on their tongue and get fussy when the bit hangs too low which happens when the cheekpieces are too loose or the bit is too wide
• A noseband that fits below the bit helps to stabilize it
• When the horse’s head approaches the vertical, the bit hangs down on the tongue
• This changes the orientation of the mouthpiece and may alter the angle of plates and lozenges in the middle of the mouthpiece that can put pressure on the tongue and palate
• The tongue can be retracted beneath the bit or used to raise the bit between the cheek teeth
• This is facilitated by a bit that is too wide or adjusted too low in the mouth
• A single-jointed bit is more likely to press against the palate than an unjointed or double-jointed bit, especially if the horse has a flat palate
• Rein tension moves the bit away from the palate
• Horses have no trouble swallowing when cantering in a collected frame with a bit and side reins
• Each horse seems to have their own repertoire of oral movements associated with the bit

Rein tension 

One of the areas I was interested in, that required developing our own equipment, was the study of rein tension. The photo below shows the first collection of rein tension data in the McPhail Center. The hierarchy in the lab is evident: 

• the graduate student carries the cable connecting the rein sensors to a laptop computer
• the lab manager runs the computer
• I ride the horse
  
  

Archival photo of the first collection of rein tension data in the McPhail Center.

Some things I’ve learned about rein tension:

• Tension changes continuously during riding with a characteristic pattern in each gait
• The minimal tension represents the mutually agreed contact between horse and rider
• Added to the baseline value are regular increases in tension due to movements of the horse’s head and neck relative to its body
  - When the head nods down, rein tension increases
• The rider’s aids are superimposed on the gait-related pattern of rein tension
  - As an example, a rebalancing half halt shows a brief increase in rein tension followed by release of tension and an overall reduction in rein tension in subsequent strides
• Riding with a piece of elastic material inserted in the rein damps the pressure on the horse’s mouth but takes away precision in the rider-horse contact
• The largest rein tensions I’ve seen occurred when the horse chose to root on the bit
  - This suggests we need to question our assumptions about what the horse finds uncomfortable or painful rather than jumping to conclusions 
  
  
  Typical rein tension patterns in walk (top graph), trot (middle graph) and canter (bottom graph). The right rein tension is shown in red and the left rein tension in blue. Note the different values on the vertical axes for the three gaits.

Pressure on the horse’s back

Equestrian sports developed when people realized that the horse’s back could carry a rider. We now know that, although the horse’s back is a convenient place for a rider to sit, there are some potential problems in terms of hollowing the horse’s back and the possibility of high-pressure areas beneath the saddle. The use of a pressure mat provides information about the total force on the horse’s back and how it’s distributed between the left and right sides or the front and back of the saddle. It can also pinpoint focal areas of high pressure that could be uncomfortable for the horse.

Things to know:

• The tree of a conventional, correctly fitted saddle distributes the rider’s weight over a large area
• When riding bareback, the rider’s entire weight acts through the seat bones resulting in concentrated areas of high pressures
• A treeless saddle also distributes the rider’s weight over a small area of the horse’s back
• A flapless saddle puts the rider in close contact with the horse and improves the rider’s stability, especially from side-to-side
• When a rider mounts using the stirrup on the left side, there is a large pressure increase on the right side of the withers to stabilize the saddle
• Habitually mounting from the same side eventually results in asymmetrical muscular development
• Blanket design affects the amount and distribution of pressure on the withers with a cut-back shape exerting the highest pressure
• The rider’s ability to coordinate with the horse’s movements is a major component of the harmony between rider and horse

Olympic studies of sporting performance in dressage and show jumping horses

My research team was chosen to collect biomechanical data during the dressage and show jumping competitions at the Olympic Games in Barcelona in 1992 and Atlanta in 1996. It was a great opportunity to analyze data from the best horses in the world at that time.

In the dressage arena, my focus was on the ’3 Ps’ – passage, piaffe and pirouettes. Here are some of the results:

• Collected canter often does not have a suspension phase
• Canter pirouette strides have a four-beat rhythm with hind-first diagonal dissociation and no suspension phases
• Canter pirouette strides are slower (879 ms) than collected canter strides (629 ms)
• Stance durations are prolonged to help the horse maintain balance in the pirouettes
• Walk pirouette strides have an irregular rhythm due to early placement of the inside hind limb which is also a balancing strategy
• Collected trot and passage are performed in a similar manner by all horses but each horse has its own interpretation of how to piaffe
• There is no suspension phase in piaffe – this would be incompatible with the requirement to lower the haunches and sit throughout the stride
  
  

In the show jumping competitions the focus was on how jumping technique and the path of the horse’s Center of Mass (CM) differed between three fence types: a vertical 1.6 m high, an oxer 1.5 m high and 1.8 m wide, and a water jump 4.5 m wide.

• Compared with the water jump, CM vertical velocity, CM peak height, and average trunk angular velocity were significantly higher for the vertical and spread fences
• Peak height of the CM coincided approximately with the middle of the oxer, it was closer to the take-off side of the water jump and closer to the landing side of the vertical fence
• The trunk had the steepest upward inclination at take off for the vertical fence 
• For each fence type, all horses tended to use similar jumping techniques 
• All horses took off at a similar distance from the base of the water jump and with a similar horizontal velocity
  - This indicates that galloping faster on the approach is not the key to success

• Horses that cleared the width of the water jump took off with a more elevated trunk angle and higher vertical velocity that allowed them to spend more time in the air and cover a longer horizontal distance while they were airborne

Physiotherapy research

One of the skills of managing a research program is recognizing emerging areas that will benefit from evidence-based information. Veterinary physiotherapy is an area in which the McPhail Center was at the forefront of investigating techniques used by equine therapists. 

• Baited (carrot) stretches activate the spinal stabilizing muscles and stimulate an increase in their size of within as little as 6 weeks
  • These muscles are thought to protect against the development of spinal arthritis
• The use of proprioceptive pastern bracelets with lightweight rings or small chains that rattle against the coronet and pastern stimulated the horse to lift the limb(s) higher as a result of greater joint flexions during the swing phase
  
  • This was useful for restoring the full range of motion in joints after immobilization or injury
  • Horses habituate quite quickly to this stimulus, so it is most effective to use the bracelets for short periods several times daily
• Leg weights attached to the pastern strengthen the muscles that raise the limb during the swing phase
  • Initially, horses over-compensate for the extra weight, but they quickly learn how much they need to increase the muscular effort 
  • The extra muscular effort persists for as long as the weights are worn – in other words, horses don’t habituate to them
• Pastern bracelets and leg weights used together have an additive effect indicating that they act via different mechanisms
• Trotting over ground poles or raised poles also increases joint flexions and is a good strengthening exercise both for the limbs and back 

Hope you enjoyed reading about some of my research. Next time we’ll take a deep dive into ground reaction forces which are an essential component of equine locomotion.