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Gait is the pattern of movement of the
limb Limb may refer to: Science and technology * Limb (anatomy), an appendage of a human or animal *Limb, a large or main branch of a tree *Limb, in astronomy, the curved edge of the apparent disk of a celestial body, e.g. lunar limb *Limb, in botany, ...
s of animals, including
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, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed,
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, the need to maneuver, and energetic efficiency. Different animal species may use different gaits due to differences in
anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having i ...
that prevent use of certain gaits, or simply due to evolved innate preferences as a result of habitat differences. While various gaits are given specific names, the complexity of biological systems and interacting with the environment make these distinctions "fuzzy" at best. Gaits are typically classified according to footfall patterns, but recent studies often prefer definitions based on mechanics. The term typically does not refer to limb-based propulsion through fluid mediums such as water or air, but rather to propulsion across a solid substrate by generating reactive forces against it (which can apply to walking while underwater as well as on land). Due to the rapidity of animal movement, simple direct observation is rarely sufficient to give any insight into the pattern of limb movement. In spite of early attempts to classify gaits based on footprints or the sound of footfalls, it was not until Eadweard Muybridge and Étienne-Jules Marey began taking rapid series of photographs that proper scientific examination of gaits could begin.


Overview

Milton Hildebrand Milton may refer to: Names * Milton (surname), a surname (and list of people with that surname) ** John Milton (1608–1674), English poet * Milton (given name) ** Milton Friedman (1912–2006), Nobel laureate in Economics, author of '' Fre ...
pioneered the contemporary scientific analysis and the classification of gaits. The movement of each limb was partitioned into a stance phase, where the foot was in contact with the ground, and a swing phase, where the foot was lifted and moved forwards. Each limb must complete a cycle in the same length of time, otherwise one limb's relationship to the others can change with time, and a steady pattern cannot occur. Thus, any gait can completely be described in terms of the beginning and end of stance phase of three limbs relative to a cycle of a reference limb, usually the left hindlimb.


Variables

Gaits are generally classed as "symmetrical" and "asymmetrical" based on limb movement. It is important to note that these terms have nothing to do with left-right symmetry. In a symmetrical gait, the left and right limbs of a pair alternate, while in an asymmetrical gait, the limbs move together. Asymmetrical gaits are sometimes termed "leaping gaits", due to the presence of a suspended phase. The key variables for gait are the duty factor and the forelimb-hindlimb phase relationship. Duty factor is simply the percent of the total cycle which a given foot is on the ground. This value will usually be the same for forelimbs and hindlimbs unless the animal is moving with a specially trained gait or is accelerating or decelerating. Duty factors over 50% are considered a "walk", while those less than 50% are considered a run. Forelimb-hindlimb phase is the temporal relationship between the limb pairs. If the same-side forelimbs and hindlimbs initiate stance phase at the same time, the phase is 0 (or 100%). If the same-side forelimb contacts the ground half of the cycle later than the hindlimb, the phase is 50%.


Physiological effects of gait

Gait choice can have effects beyond immediate changes in limb movement and speed, notably in terms of ventilation. Because they lack a
diaphragm Diaphragm may refer to: Anatomy * Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Pelvic diaphragm or pelvic floor, a pelvic structure * Urogenital diaphragm or triangular ligament, a pelvic structure Other * Diap ...
, lizards and salamanders must expand and contract their body wall in order to force air in and out of their lungs, but these are the same muscles used to laterally undulate the body during locomotion. Thus, they cannot move and breathe at the same time, a situation called Carrier's constraint, though some, such as monitor lizards, can circumvent this restriction via buccal pumping. In contrast, the spinal flexion of a galloping mammal causes the abdominal viscera to act as a piston, inflating and deflating the lungs as the animal's spine flexes and extends, increasing ventilation and allowing greater
oxygen exchange The pulmonary circulation is a division of the circulatory system in all vertebrates. The circuit begins with deoxygenated blood returned from the body to the right atrium of the heart where it is pumped out from the right ventricle to the lun ...
.


Differences between species

Any given animal uses a relatively restricted set of gaits, and different species use different gaits. Almost all animals are capable of symmetrical gaits, while asymmetrical gaits are largely confined to
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...
s, who are capable of enough spinal flexion to increase stride length (though small
crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...
ns are capable of using a bounding gait). Lateral sequence gaits during walking and running are most common in mammals,Lemelin P, Schmitt D and Cartmill M. 2003. Footfall patterns and interlimb co-ordination in opossums (Family Didelphidae): evidence for the evolution of diagonal-sequence walking gaits in primates. J. Zool. Lond. 260:423-429
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/ref> but arboreal mammals such as
monkey Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as the simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes, which constitutes an incomple ...
s, some opossums, and kinkajous use diagonal sequence walks for enhanced stability. Diagonal sequence walks and runs (aka trots) are most frequently used by sprawling
tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...
s such as
salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...
s and lizards, due to the lateral oscillations of their bodies during movement.
Bipeds Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' a ...
are a unique case, and most bipeds will display only three gaits—walking, running, and hopping—during natural locomotion. Other gaits, such as human skipping, are not used without deliberate effort.


Energy-based gait classification

While gaits can be classified by footfall, new work involving whole-body
kinematics Kinematics is a subfield of physics, developed in classical mechanics, that describes the motion of points, bodies (objects), and systems of bodies (groups of objects) without considering the forces that cause them to move. Kinematics, as a fiel ...
and force-plate records has given rise to an alternative classification scheme, based on the mechanics of the movement. In this scheme, movements are divided into walking and running. Walking gaits are all characterized by a "vaulting" movement of the body over the legs, frequently described as an inverted pendulum (displaying fluctuations in kinetic and
potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors. Common types of potential energy include the gravitational potenti ...
which are out of phase), a mechanism described by
Giovanni Cavagna Giovanni Cavagna (born 30 May 1934) is a physiologist and Emeritus Professor of Human Physiology at the University of Milan. His research focuses on muscle physiology, biomechanical principles of terrestrial locomotion in humans and other ...
. In running, the kinetic and potential energy fluctuate in-phase, and the energy change is passed on to
muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of mus ...
s,
bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
s,
tendon A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...
s and
ligament A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the: * Peritoneal l ...
s acting as springs (thus it is described by the spring-mass model).


Energetics

Speed generally governs gait selection, with quadrupedal mammals moving from a walk to a run to a gallop as speed increases. Each of these gaits has an optimum speed, at which the minimum calories per metre are consumed, and costs increase at slower or faster speeds. Gait transitions occur near the speed where the cost of a fast walk becomes higher than the cost of a slow run. Unrestrained animals will typically move at the optimum speed for their gait to minimize energy cost. The
cost of transport The energy cost of transport quantifies the energy efficiency of transporting an animal or vehicle from one place to another. As a dimensionless quantity, it allows for the comparison of dissimilar animals or modes of transportation. It has a wide ...
is used to compare the energetics of different gaits, as well as the gaits of different animals.


Non-tetrapod gaits

In spite of the differences in leg number shown in terrestrial
vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...
s, according to the inverted pendulum model of walking and spring-mass model of running, "walks" and "runs" are seen in animals with 2, 4, 6, or more legs. The term "gait" has even been applied to flying and swimming organisms that produce distinct patterns of wake vortices.


See also

*
Bipedal gait cycle A (bipedal) gait cycle is the time period or sequence of events or movements during locomotion in which one foot contacts the ground to when that same foot again contacts the ground, and involves propulsion of the centre of gravity In physics, ...
* Gait analysis *
Gait abnormality Gait abnormality is a deviation from normal walking (gait). Watching a patient walk is the most important part of the neurological examination. Normal gait requires that many systems, including strength, sensation and coordination, function in an ...
* Gait (dog) *
Gait (human) A gait is a pattern of limb movements made during locomotion. Human gaits are the various ways in which humans can move, either naturally or as a result of specialized training. Human gait is defined as bipedal, biphasic forward propulsion o ...
*
Horse gait Horses can use various gaits (patterns of leg movement) during locomotion across solid ground, either naturally or as a result of specialized training by humans.Ensminger, M. E. ''Horses and Horsemanship'' 6th edition USA: Interstate Publishe ...
*
Parkinsonian gait Parkinsonian gait (or festinating gait, from Latin ''festinare'' o hurry is the type of gait exhibited by patients with Parkinson's disease (PD). It is often described by people with Parkinson's as feeling like being stuck in place, when initi ...


References

* * * * * * {{fins, limbs and wings Terrestrial locomotion Articles containing video clips