Information About Gaits
General Information
Gait refers to a pattern of limb actions that an animal uses repetitively during locomotion. Among different animals and within an individual animal over time, one can expect to see a variety of locomotion patterns. Usually, however, a particular gait pattern can be identified as an expression of one of the basic gait types. Types of gaits recognized in cursorial quadrupeds include: walk (& amble), trot, pace (rack), canter, and gallop.

The canter and gallop are regarded as asymmetrical gaits because right and left limbs have different actions (the actions are not mirror images). Asymmetric gaits favor turning toward one side or the other, and an animal is said to be in a "right/left lead" according to which side it is predisposed to turn toward, at the canter or gallop. Animals control which lead they are using, and they switch leads to suit external circumstances or to minimize fatigue.

Though quadrupeds have just a few defined gaits, an individual animal may exhibit great variation in gait. Some of the variation is due to species or breed conformation differences, some is due to training, experience, or health status, some is due to terrain, emotional status, degree of exhaustion, etc. Ultimately, an animal can be expected to choose a gait variation that is the most convenient under existing circumstances.

As you begin to study the limb patterns that.

Locomotion and diet are linked in evolution. Carnivores require multipurpose limbs (used for both running & manipulation); whereas, herbivore limbs, devoted entirely to running, can be more specialized for locomotion. Herbivores with roughage diets and bulky abdominal visceral have less flexible trunks and rely more on limb elongation. Carnivores are fast because they have flexible trunks, which is possible because they have a small-volume meat diet (which is why they need multipurpose limbs in the first place).

Biomechanical Considerations
Cursorial quadrupeds are designed for forward locomotion and they have relative difficulty moving backwards. The normal center of gravity (CG) is located just caudal to the thoracic limbs. The CG can be shifted forward by lowering the head and neck and backward by raising the head. Moving the head to the side shifts the CG laterally. The tail (depending on its length and mass) also contributes to longitudinal and lateral shifts in the CG.

Forward motion is generally initiated by one hind limb, which shifts the CG forward and toward the contralateral forelimb (which reaches forward to support the shifted CG). At slow gaits (walk) the CG rhythmically oscillates left/right and the trunk, head, and tail swing from side to side to maintain equilibrium. At rapid gaits, forward momentum and inertia are increased and there is less lateral oscillation (just like a bicycle). As speed increases, fewer limbs provide simultaneous support and the "feet" impact the ground nearer the median plane to maintain balance during propulsion.

The pelvic limbs are designed for propulsion. They accelerate the CG forward and upward. Pelvic limbs are relatively long and angular, heavily muscled, and connected directly to the vertebral column (coxofemoral and sacroiliac joints). Epaxial muscle contraction assists in elevating the CG. Locomotion proceeds by repetitively throwing the CG forward and then catching it. Elevation of the CG is necessary to extend the duration of forward motion which is temporally limited by the pull of gravity.

The thoracic limbs are designed for support (catching the CG). Relative to pelvic limbs, they are shorter and straighter and connected to the trunk by fibro-muscular attachments. They regularly provide upward propulsion and directional stability, but they contribute to forward propulsion only under certain circumstances (when retracting in contact with the ground while forward of the CG; when the animal is pulling a load that shifts the CG caudally).

Energy conservation. Both fore and hind limbs are designed to recapture some of the energy expended in elevating the trunk to counteract gravity. The weight of the falling trunk does work in stretching limb muscles and ligaments (storing potential energy) which can rebound (become kinetic energy) to elevate the trunk as the CG passes forward of the weight bearing limb. Due to elastic rebound, galloping gaits are metabolically more economical (less oxygen consumption) than the trot gait at high speeds.

Gait velocity. During locomotion each limb is swung forward and then retracted to contact the ground. As gait velocity increases, limbs are increasingly flexed during forward swing to decrease angular mass and facilitate speed of protraction. Ideally, at the moment of paw/hoof impact with the ground, the velocity of limb retraction should equal the forward speed of the animal (i.e., the speed with which the ground is receding). Thus the paw/hoof would impact the ground at zero velocity which minimizes potentially traumatic accelerations.

Bibliography
The subject matter content of this web site (originally presented in a HyperCard document) was obtained from the following sources:

Equiworld.net: Gaits & Biomechanics (http://www.equiworld.net/uk/horsecare/gaits/)

Fletcher, T.F. 2002. Anatomical Adaptation for Cursoial Locomotion (http://vanat.cvm.umn.edu:16080/run/)

Gambaryan, P.P. 1974. How Mammals Run. New York; John Wiley & Sons.

Gray, J. 1968. Animal Locomotion. London; William Clowes & Sons, Ltd.

Hollenbeck, L. 1971. The Dynamics of Canine Gait. Erie, PA; A-K-D Printing Co.

McDowell, L. 1966. The Dog in Action. New York; Howell Book House, Inc.

Morrris, S. Classical Dressage Notebook: The Gaits The Walk (http://www.classicaldressage.co.uk/TheGaits/the_gaits.html)

Nikel, R., Schummer, A., Seiferle, E., Frewein, J., Wilkens, H., and Wille, K-H. The Locomotor System of Domestic Mammals. Vol. 1 of The Anatomy of Domestic Animals. Translated W.G. Siller and W.M. Stokoe; 1986. New York; Springer-Verlag.

Muybridge, E. Animals in Motion. Ed. L.S. Brown 1957. New York; Dover Publications.

Roberts, T.D.M. 1967. Neurophysiology of Postural Mechanisms. New York; Plenum Press. pp. 153-175.

Wikipedia, the free encyclopedia: Horse Gaits (http://en.wikipedia.org/wiki/Horse_gaits.html)

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