Biomechanics of motion, part II

Objectives Name the extensor and three flexor muscles on the foreleg and rear leg List the two phases of a stride Name three factors of a gait that determine a horse’s speed Define terms as they relate to gaits Describe the walk, trot, canter and gallop Discuss conformation in movement List and describe six common defects in a horse’s way of going Discuss center of gravity

Muscles involved in gaits Front leg extensors Brachiocephalicus Supraspinatus Triceps brachii Oblique carpal extensor Lateral digital extensor Common digital extensor Front leg flexors Teres major Latissimus dorsi Biceps brachii Flexor carpi radialis Flexor carpi ulnarus Deep digital flexor

Muscles involved in gaits Hind leg extensors Biceps femoris Semitendinous Semimembraneous Gluteus medius Quadriceps femoris Gastrocnemius Long digital extensor Lateral digital extnsor Flexors of the hind leg Iliacus Popliteus Deep digital flexor Superficial digital flexor

Components of a stride Stride stance – weight bearing phase Stride Suspension – swing or non weight bearing

Terminology of Movement Abductors – move a horse’s leg away from the center plane Adductors – move a horse’s leg toward the center plane Flexors bend a joint Extensors straighten a joint. Gait is an equine’s way of going or moving its legs during movement beat refers to the time a foot or two feet simultaneously hit the ground. Step is the distance between the imprints of the two front legs or the two hind legs

A stride is the distance between successive imprints of the same foot Directness, also called trueness is the line in which the foot is carried forward during the stride. Spring is the manner in which weight settles back on the supporting leg at the completion of the stride. Balance refers to the ability of the equine to coordinate action, go composed and in form

Components of a Stride A stride has two phases Stride stance is the weight bearing phase Stride suspension or swing is the non-weight bearing phase

The speed of a horse is affected by: Length of stride, rapidity or frequency of stride and overlap time Overlap time is the time on the ground versus the time off the ground

Natural Gaits (no training) Walk is a slow, even, four-beat gait The sequence of hoof-beats is first – left hind, next, left fore, then- right hind, and finally – right fore Both feet on one side strike the ground before the feet on the opposite side strike the ground

Walk Walk: The walk is a natural 4-beat movement. The horse always has two or three hooves on the ground. The walk is the slowest natural gait, it is the steadiest and most comfortable. The horse lifts his hooves as follows:              (1st beat) right hind leg (2nd beat) right fore leg (3rd beat) left hind leg (4th beat) left fore leg

Trot is a two-beat gait where the diagonal fore and hind legs act together A period of suspension when all four feet are off the ground occurs between each beat There are different styles of trotting: road horse trot is fast- stepping, hackney trot and heavy harness trot are high- stepping forms of trotting

Trot (Jog) Trot: The trot is a steady 2-beat movement. Since the trot has two beats each stride and a moment in mid-air, it is more comfortable for the rider (and the horse) to rise up and down every-other beat (this is called "posting"). The horse lifts his hooves as follows:              (1st beat) right fore / left hind (2nd beat) left fore / right hind

Canter or lope is a three beat collected gait where the equine carries more weight on its haunches or rear quarter Sequence of hoof-beats for canter is first – right rear hoof, next- left rear and right front striking the ground at the same time and last- left front hoof. Canter is performed in slow, animated, rhythm.

Canter (Lope) Canter: The canter is a 3-beat movement. The horse lifts his hooves as follows:              The Right-Lead Canter: (1st beat) left hind leg (2nd beat) right hind / left fore (3rd beat) right fore leg

Gallop or run is a fast, four-beat gait Sequence of hoof-beats is first- one hind foot, next- the other hind foot, then- the diagonal forefoot followed by the remaining forefoot A period of suspension follows the four beats. Racehorses use the gallop or run gait

Gallop Gallop: The gallop is a 4-beat movement. This gait is similar to the canter, but the horse's legs move one at a time. The gallop feels just like a fast canter. The horse lifts his hooves as follows:              The Right-Lead Gallop: (1st beat) left hind leg (2nd beat) right hind leg (3rd beat) left fore leg (4th beat) right fore leg

Other Gaits Pace is a two-beat, lateral gait used for speed with the fore and hind legs on the same side moving together. The gait has a rolling motion. Slow gait or stepping pace is a show gait that uses a lateral, four beat gait where the front foot on the right is followed by the hind foot on the right

Rack (sometimes called the single foot) is an even, fast four-beat lateral gait that is hard on the equine’s forelegs due to increased amount of concussion from the excessive leg movement. Rack is easy on the rider

Running walk is the fast walk of a Tennessee walking horse where the horse travels with a gliding motions as a result of extending its hind leg forward to overstep the forefoot print. Back is actually trotting in reverse

Gait Defects May interfere or cause injury to the equine Forging is the striking of the toe of the hind foot against the sole of the forefoot. Fig. 6 - 11 Interfering is when the foot of the striding leg strikes the supporting leg and usually occurs between the supporting front leg a striding front leg or between a supporting hind leg and a striding hind leg. Fig 6-12

Winding is twisting the front leg around in front of the supporting leg as each stride is taken and is common with wide-chested horses Other gait defects include scalping, speedy-cutting, cross-firing, pointing, swelling, trappy, pounding and rolling. Fig 6-14, Fig. 6-15

Center of Gravity, Conformation and Gaits Most commonly located in the middle of the rib cage just caudal to the line separating the cranial and middle thirds of the body Because the center of gravity is located more cranially, the forelimbs bear 60-65% of the equine’s weight resulting in more stress and lameness in the forelimbs

Conformation for structure of the horse can be generalized to say that basically an equine that stands straight is likely to move straight and true.