Editing Gait

{{Short description|Pattern of movement of the limbs of animals}}
{{about|gaits of all animals}}
[[File:Elephant walking.gif|right|thumb|Elephant walking]]

'''Gait''' is the pattern of [[Motion (physics)|movement]] of the [[limb (anatomy)|limb]]s of [[animals]], including [[Gait (human)|humans]], during [[Animal locomotion|locomotion]] over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, [[terrain]], the need to [[wikt:maneuver|maneuver]], and energetic efficiency. Different animal species may use different gaits due to differences in [[anatomy]] 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.

{{Wiktionary|gait}}

==Overview==
[[Milton Hildebrand]] 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.<ref>{{cite journal |last1=Hildebrand |first1=Milton |title=The Quadrupedal Gaits of Vertebrates: The timing of leg movements relates to balance, body shape, agility, speed, and energy expenditure |journal=BioScience |date=1 December 1989 |volume=39 |issue=11 |page=766 |doi=10.2307/1311182|jstor=1311182 }}</ref><ref name="TaschMoubarak2008">{{cite book|last1=Tasch|first1=U.|title=Volume 2: Automotive Systems; Bioengineering and Biomedical Technology; Computational Mechanics; Controls; Dynamical Systems|last2=Moubarak|first2=P.|last3=Tang|first3=W.|last4=Zhu|first4=L.|last5=Lovering|first5=R. M.|last6=Roche|first6=J.|last7=Bloch|first7=R. J.|chapter=An Instrument That Simultaneously Measures Spatiotemporal Gait Parameters and Ground Reaction Forces of Locomoting Rats |year=2008|pages=45–49|doi=10.1115/ESDA2008-59085|isbn=978-0-7918-4836-4}}</ref> Each limb must complete a [[period (physics)|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==
[[File:Gait graphs v2.png|thumb|500px|Gait graphs in the style of Hildebrand. Dark areas indicate times of contact, bottom axis is % of cycle]]
Gaits are generally classed as "symmetrical" and "asymmetrical" based on limb movement. 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 [[Variable (research)|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 [[Acceleration|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 [[Time|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 (physiology)|ventilation]]. Because they lack a [[Thoracic diaphragm|diaphragm]], 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 [[breathing|oxygen exchange]].

==Differences between species==
[[File:Gait-of-healthy-Hamster.ogv|200px|thumb|left|A hamster walking on a transparent treadmill.]] [[File:Alternating_Tripod_Gait.webm|200px|thumb|right|Alternating tripod gait of walking desert ants.]]

Animals typically use different gaits in a speed-dependent manner. Almost all animals are capable of symmetrical gaits, while asymmetrical gaits are largely confined to mammals, who are capable of enough spinal flexion to increase stride length (though small crocodilians are capable of using a bounding gait). Lateral sequence gaits during walking and running are most common in mammals,[3] but arboreal mammals such as monkeys, some opossums, and kinkajous use diagonal sequence walks for enhanced stability.[3] Diagonal sequence walks and runs (aka trots) are most frequently used by sprawling tetrapods such as salamanders and lizards, due to the lateral oscillations of their bodies during movement. Bipeds 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.

Hexapod gaits have also been well characterized, particularly for drosophila and stick insects (Phasmatodea). Drosophila use a [[tripod gait]] where 3 legs swing together while 3 legs remain on the ground in stance.<ref>{{cite journal | vauthors = Strauss R, Heisenberg M | title = Coordination of legs during straight walking and turning in Drosophila melanogaster | journal = Journal of Comparative Physiology A | volume = 167 | issue = 3 | pages = 403–12 | date = August 1990 | pmid = 2121965 | doi = 10.1007/BF00192575 | s2cid = 12965869 }}</ref> However, variability in gait is continuous. Flies do not show distinct transitions between gaits but are more likely to walk in a tripod configuration at higher speeds. At lower speeds, they are more likely to walk with 4 or 5 legs in stance.<ref>{{cite journal | vauthors = DeAngelis BD, Zavatone-Veth JA, Clark DA | title = Drosophila | journal = eLife | volume = 8 | date = June 2019 | pmid = 31250807 | pmc = 6598772 | doi = 10.7554/eLife.46409 | doi-access = free }}</ref> Tetrapod coordination (when 4 legs are in stance) is where diagonally opposite pairs of legs swing together. Wave (sometimes called a metachronal wave) describes walking where only 1 leg enters swing at a time. This movement propagates from back to front on one side of the body and then the opposite. Stick Insects, a larger hexapod, only shows a tripod gait during the larval stage. As adults at low speeds, they are most likely to walk in a metachronal wave, where only 1 leg swings at a time. At higher speeds, they walk in a tetrapod coordination with 2 legs paired in swing or a metachronal wave, only moving one leg at a time.<ref>{{cite journal | vauthors = Ayali A, Borgmann A, Buschges A, Cousin-Fuchs E, Daun-Gruhn S, Holmes P| title = The comparative investigation of the stick insect and cockroach models in study of animal locomotion | journal = Current Opinion in Insect Science  | issue = 12 | pages = 1–10 | date = 2015 | doi = 10.1016/j.cois.2015.07.004 }}</ref>

==Energy-based gait classification==
While gaits can be classified by footfall, new work involving whole-body [[kinematics]] and force-plate records has given rise to an alternative classification scheme, based on the mechanics of the [[Motion (physics)|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]] which are out of phase), a mechanism described by [[Giovanni Cavagna]]. In running, the kinetic and potential energy fluctuate in-phase, and the energy change is passed on to [[muscle]]s, [[bone]]s, [[tendon]]s and [[ligament]]s acting as springs (thus it is described by the [[Harmonic oscillator|spring-mass model]]).

==Energetics==
[[File:Muybridge Buffalo galloping.gif|right|thumb|Bison galloping]]

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]] 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 animal|terrestrial]] [[vertebrate]]s, according to the [[inverted pendulum]] model of walking and [[Harmonic oscillator|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]]
* [[Gait analysis]]
* [[Gait abnormality]]
* [[Gait (dog)]]
* [[Gait (human)]]
* [[Horse gait]]
* [[Parkinsonian gait]]

==References==
{{Commons category|Gait}}
{{Reflist}}
{{more footnotes needed|date=August 2009}}
* {{cite journal
 | last = Hildebrand | first = M.
 | title = Vertebrate locomotion an introduction how does an animal's body move itself along?
 | journal = BioScience | year = 1989 | issue = 11 | pages = 764–765
 | jstor = 1311182
 | volume = 39 | doi=10.1093/bioscience/39.11.764
}}
* {{cite journal
 | last1 = Hoyt | first1 = D. F. | last2 = Taylor | first2 = R. C.
 | title = Gait and the energetics of locomotion in horses
 | journal = Nature | year = 1981 | issue = 5820 | pages = 239–240
 | doi= 10.1038/292239a0
 | volume = 292| bibcode = 1981Natur.292..239H | s2cid = 26841475 }}
* {{cite journal
 | last = Carrier | first = D.
 | title = Lung ventilation during walking and running in four species of lizards
 | journal = Experimental Biology | year = 1987 | issue =   1| pages = 33–42
 | pmid=3666097 | volume=47
}}
* {{cite journal
 | last1 = Bramble | first1 = D. M. | last2 = Carrier | first2 = D. R
 | s2cid = 23551439 | title = Running and breathing in mammals
 | journal = Science | year = 1983 | issue =   4582| pages = 251–256
 | pmid = 6849136
 | doi = 10.1126/science.6849136
 | volume = 219
| bibcode = 1983Sci...219..251B }}
* {{cite journal
 | last1 = Blickhan | first1 = R. | last2 = Full | first2 = R. J.
 | title = Similarity in multilegged locomotion: Bouncing like a monopode
 | journal = Journal of Comparative Physiology A | year = 1993 | volume = 173 | issue = 5 | pages = 509–517
 | doi=10.1007/bf00197760
| s2cid = 19751464 }}
* {{cite journal
 | last1 = Cavagna | first1 = G. A. | last2 = Heglund | first2 = N. C. | last3 = Taylor | first3 = R. C.
 | s2cid = 15842774 | title = Mechanical work in terrestrial locomotion: two basic mechanisms for minimizing energy expenditure
 | journal = Am. J. Physiol. | year = 1977 | issue =   5| pages = R243–R261
 | pmid = 411381
 | volume = 233
| doi = 10.1152/ajpregu.1977.233.5.R243 }}

{{locomotion|state=expanded}}
{{fins, limbs and wings}}

[[Category:Terrestrial locomotion]]
[[Category:Articles containing video clips]]