Lower Limb Research at the Bluegrass Laminitis Symposium

Probably the foremost biomechanics researcher in the country, Hilary Clayton, BVMS, PhD, MRCVS, McPhail Dressage Chair in Equine Sports Medicine at Michigan State University's McPhail Equine Performance Center, discussed recent lower limb research during the 16th annual Bluegrass Laminitis Symposium. Some of the studies she described were performed in collaboration with researchers at California State Polytechnic University.

She initially focused on kinematics (motion) of the fore and hind limbs. "The maximum velocity of the horse's hoof is about double that of the horse's maximum velocity," she noted. "So for a horse that's running at about 40 mph, the maximal speed of the hoof as it swings forward is about 80 mph. That's pretty darn fast."

She then compared durations of the swing and stance phases of the limbs during trotting. "Stride duration, which is the sum of stance and swing durations, decreases as speed increases. In the forelimb, the swing phase doesn't change much with increased speed," she said. "So, the reduction in stride duration is from a decreased duration of the stance phase--the leg spends the same amount of time in the air, but less on the ground." In the hind limb, both the swing phase and the stance phase durations decrease with increased speed.

"The limbs push against the ground during the stance phase to provide propulsion. When the stance phase shortens with increased speed, the horse must generate higher forces to compensate for the decrease in contact time," she said. "With humans, and likely also with horses, the ability to achieve high sprinting speeds is influenced more by the ability to generate large forces in the stance phase than the ability to move the limb rapidly during swing."

Heavy Shoes

Since this symposium's attendees were mostly farriers, they were quite interested in shoe research. Clayton discussed research on the effect of using shoes or increasing the weight of the shoes, noting that there was no apparent difference during the stance phase, but adding weight to the hoof increased animation during the swing phase. She described increased carpal (knee) and fetlock flexion, resulting in a higher peak flight arc.

"The proximal (upper) limb is decelerated and retracted prior to ground contact, resulting in a whiplash effect in the distal limb," she added. "With heavy shoes, the whiplash effect is exaggerated. As a result, the pastern tends to be more horizontal during late swing, and the horse has more exaggerated heel-first ground contact. What we found is that you can change the end of the stance phase and early swing phase (with heavier shoes), but the horse can re-establish normal conditions at impact unless the speeds are very high or the shoes are very heavy."

Muscles are also affected--Clayton explained that extra weight causes the elbow flexors to work harder in early swing to pull the limb forward, and the elbow extensors to work harder late in swing to initiate retraction. This principle can be used to train for increased muscle strength. For a short time following removal of heavy shoes, the horse is likely to continue to show the same animation as he did with heavier shoes due to muscle memory.


Torque, or turning force, is required to flex and extend the joints. Measuring normal forces is essential to understanding how different factors can change those forces for better and worse.

"Muscles move or stabilize joints by creating torque," Clayton said. "Breakover at the end of stance involves quite a bit of leverage, or torque at the coffin joint, which acts as the fulcrum during breakover. Changes in hoof angle and toe length affect coffin joint torque.

"It's not a simple relationship between hoof conformation and coffin joint torque; the more I know, the less I know," she continued. "With an increase in the hoof angle, tension decreases in the deep digital flexor tendon (DDFT) and breakover is delayed. Because the breakover is delayed, the ground reaction force is lower when breakover starts and there is less torque at the coffin joint. Conversely, with a decreased hoof angle, DDFT tension increases, which may hasten breakover, but with an increased torque at the coffin joint... Coffin joint torque during breakover is affected by both the magnitude and distribution of the DDFT force and the ground reaction force. The components cannot be considered in isolation, however.

"In the next year or so, I'm hoping that we can do some major projects on the hoof," Clayton said. "The effects of farriery manipulations are not always intuitive. What we need now is enough money to really study these concepts and prove or disprove them."

For more information, see article #4105.

Coming in May...More Bluegrass Laminitis Symposium Coverage

The 16th annual Bluegrass Laminitis Symposium, held Jan. 16-18, 2003, in Louisville, Ky., easily lived up to the symposium's reputation of providing cutting-edge, hands-on hoof care information that's useful to veterinarians, farriers, and horse owners. Club feet, venograms, balanced shoeing, Parelli handling methods, biomechanics research, and much more graced this year's program. Look for more information on the symposium online and in the May issue of The Horse and online at: www.TheHorse.com/BGLS.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from TheHorse.com. Learn More

Free Newsletters

Sign up for the latest in:

From our partners