1. Biomechanics of motion, part II

2. 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

3. 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

4. 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

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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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.

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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
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

22. 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

23. 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

24. 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.