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Animal locomotion



 
 
In biomechanics
Biomechanics

Biomechanics is the application of mechanical principles to living organisms. This includes bioengineering, the research and analysis of the mechanics of living organisms and the application of engineering principles to and from biological systems....
, animal locomotion is the study of how animal
Animal

Animals are a major group of multicellular, eukaryotic organisms of the Kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life....
s move
Motion (physics)

In physics, motion means a constant change in the location of a body. Change in motion is the result of applied force. Motion is typically described in terms of velocity, acceleration, Displacement , and time....
. Most animals move in order to find food, a mate, escape predators, find suitable microhabitats, etc. The ability to do so is therefore essential to their survival, and the nature of this relationship often governs the selective pressures that shape a particular organism's locomotion.






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In biomechanics
Biomechanics

Biomechanics is the application of mechanical principles to living organisms. This includes bioengineering, the research and analysis of the mechanics of living organisms and the application of engineering principles to and from biological systems....
, animal locomotion is the study of how animal
Animal

Animals are a major group of multicellular, eukaryotic organisms of the Kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life....
s move
Motion (physics)

In physics, motion means a constant change in the location of a body. Change in motion is the result of applied force. Motion is typically described in terms of velocity, acceleration, Displacement , and time....
. Most animals move in order to find food, a mate, escape predators, find suitable microhabitats, etc. The ability to do so is therefore essential to their survival, and the nature of this relationship often governs the selective pressures that shape a particular organism's locomotion. For instance, a migratory animal which moves hundreds or even thousands of miles (such as the Arctic Tern
Arctic Tern

The Arctic Tern is a seabird of the tern family Sternidae. This bird has a :wiktionary:circumpolar distribution, breeding colonially in Arctic and sub-Arctic regions of Europe, Asia, and North America ....
) is more likely to have a mechanism of locomotion which costs very little energy per unit distance, while an animal which primarily moves in order to quickly escape predators (such as a frog
Frog

Frogs are amphibians in the order Anura , formerly referred to as Salientia . The name frog derives from Old English language frogga, , cognate with Sanskrit plava , probably deriving from Proto-Indo-European language praw = "to jump"....
) is likely to have costly but very fast locomotion, since it can always eat more if it escapes.

Locomotion requires energy
Energy

In physics, energy is a scalar physical quantity that describes the amount of Work_ that can be performed by a force. Energy is an attribute of objects and systems that is subject to a conservation law....
 to overcome friction
Friction

File:Friction alt.svgFriction is the force resisting the relative lateral motion of solid surfaces, fluid layers, or material elements in contact....
, drag
Drag

Drag may refer to:...
, inertia
Inertia

File:192447main 017 law of inertia.oggInertia is the resistance of an object to a change in its state of motion. The principle of inertia is one of the fundamental principles of classical physics which are used to describe the Motion of matter and how it is affected by applied forces....
, and gravity, though in many circumstances some of these factors are negligible. In terrestrial
Terrestrial planet

A terrestrial planet, telluric planet, rocky planet or inner planet is a planet that is primarily composed of silicate Rock s....
 environments gravity must be overcome, though the drag of air is much less of an issue. In aqueous environments however, friction (or drag) becomes the major challenge, with gravity being less of a concern. Although animals with natural buoyancy
Buoyancy

In physics, buoyancy is the upward force that keeps things afloat. The net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body....
 need not expend much energy maintaining vertical position, though some will naturally sink and must expend energy to remain afloat. Drag may also present a problem in flight
Flight

Flight is the process by which an object moves either through the air, or movement beyond earth's atmosphere , by aerodynamically generating Lift , propulsion or Lighter than air using buoyancy, or by simple ballistic movement....
, and the aerodynamically efficient body shapes of bird
Bird

Birds are wing, Bipedalismal, endothermic , vertebrate animals that lay egg . There are around 10,000 living species, making them the most numerous tetrapod vertebrates....
s highlight this point. Flight presents a different problem from movement in water however, as there is no way for a living organism to have lower density
Density

The density of a material is defined as its mass per unit volume. The symbol of density is ....
 than air. Limbless organisms moving on land must often contend with surface friction, but do not usually need to expend significant energy to counteract gravity.

Newton's third law of motion
Newton's laws of motion

Newton's laws of motion are three physical laws that form the basis for classical mechanics, Direct relationship the forces acting on a Physical body to the motion of the body....
 is widely used in the study of animal locomotion: if at rest, to move forwards an animal must push something backwards. Terrestrial animals must push the solid ground, swimming and flying animals must push against a fluid
Fluid

A fluid is defined as a substance that continually deforms under an applied shear stress. All liquids and all gases are fluids. Fluids are a subset of the Phase and include liquids, gas, Plasma physics and, to some extent, plasticity ....
 or gas
Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
 (either water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
 or air
AIR

Air is the part of Earth's atmosphere that humans breath and as such Air .Air may also refer to:...
). The effect of forces during locomotion on the design of the skeletal system is also important, as is the interaction between locomotion and muscle physiology, in determining how the structures and effectors of locomotion enable of limit animal movement.

Introduction

Animals move through a variety of fluids, such as water, air and mud. Some, for example seal
Pinniped

Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae ....
s and otter
Otter

Otters are semi-aquatic fish-eating mammals. The otter Rank Lutrinae forms part of the Family Mustelidae, which also includes weasels, polecats, badgers, as well as others....
s, move through more than one type of fluid. In some cases locomotion is facilitated by the substrate on which they move. Forms of locomotion include:

Through a fluid medium


Swimming
In the water staying afloat is possible through buoyancy. Provided an aquatic animal's body is no denser than its aqueous environment, it should be able to stay afloat well enough. Though this means little energy need be expended maintaining vertical position, it makes movement in the horizontal plane much more difficult. The drag
Drag (physics)

The term drag is widely used in Physics and Engineering and is central to the field of fluid dynamics. "Drag" refers to forces that oppose the motion of a solid object through a fluid ....
 encountered in water is much higher than that of air, which is almost negligible at low speeds. Body shape is therefore important for efficient movement, which is essential for basic functions like catching prey
Predation

In ecology, predation describes a biological interaction where a predator feeds on its prey, the organism that is attacked. Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of the prey....
. A fusiform, torpedo
Torpedo

Note: Prior to 1900, in naval usage "torpedo" could also refer to what today is called a naval mine. For that usage, see naval mine.The modern torpedo is a self-propelled explosive projectile weapon, launched above or below the water surface, propelled underwater toward a target, and designed to detonate on contact or in proximity t...
-like body form is seen in many marine animals, though the mechanisms they employ for movement are diverse. Movement of the body may be from side to side, as in shark
Shark

Sharks are a type of fish with a full Cartilage skeleton and a highly Streamlines, streaklines and pathlinesd body. They respire with the use of five to seven gill slits....
s and many fish
Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
es, or up and down, as in marine mammal
Marine mammal

Marine mammals are a diverse group of roughly 120 species of mammal that are primarily ocean-dwelling or depend on the ocean for food. They include the cetaceans , the sirenians , the pinnipeds , and several otters ....
s. Other animals, such as those from the class Cephalopoda, use jet-propulsion, taking in water then squirting it back out in an explosive burst. Others may rely predominantly on their limbs, much as humans do when swimming. Though life on land originated from the seas, terrestrial animals have returned to an aquatic lifestyle on several occasions, such as the fully aquatic cetaceans, now far removed from their terrestrial ancestors.

Flight
Gravity is a major problem for flight through the air. Because it is impossible for any organism to approach the density of air, flying animals must generate enough lift
Lift (force)

In the context of a fluid flow relative to a body, the lift force is the Vector #Vector components of the aerodynamic force that is perpendicular to the oncoming flow direction....
 to ascend and remain airborne. Wing shape is crucial in achieving this, generating a pressure gradient that results in an upward force on the animal' body. The same principle applies to airplanes, the wings of which are also airfoil
Airfoil

An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section.An airfoil-shaped body moved through a fluid produces a force perpendicular to the motion called lift ....
s. Unlike aircraft however, flying animals must be very light to achieve flight, the largest birds being around 20 kilograms. Other structural modifications of flying animals include reduced and redistributed body weight, fusiform shape and powerful flight muscles.

Rather than fly, some animals simply reduce their rate of falling by gliding. Flight has independently
Convergent evolution

Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action....
 evolved at least four times, in the insect
Insect flight

Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities....
s, pterosaur
Pterosaur

Pterosaurs were flying reptiles of the clade or Order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight....
s, bird
Bird flight

Flight is the main mode of animal locomotion used by most of the world's bird species. Flight assists birds while feeding, breeding and avoiding predation....
s, and bat
Bat

Bats are mammals in the order Chiroptera. The forelimbs of all bats are developed as wings, making them the only mammals naturally capable of sustained flight ....
s. Gliding has evolved on many more occasions. The advantage gliding provides to arboreal
Arboreal

Arboreal is a word meaning "related to or resembling trees". Its meaning comes from the Latin arbor, meaning tree.In biology, an arboreal animal is one which inhabits or spends large amounts of time in trees or Shrubes....
 animals provides a bridge for the evolution of flight.

On a substrate


Terrestrial
Forms of locomotion on land include walking, running, hopping or jumping
Jumping

Jumping or leaping is a form of locomotion or movement in which an organism propels itself through the air along a ballistic trajectory....
, and crawling or slithering. Here friction and buoyancy are not longer an issue, but a strong skeletal and muscular framework are required in most terrestrial animals for structural support. Each step also requires much energy to overcome inertia
Inertia

File:192447main 017 law of inertia.oggInertia is the resistance of an object to a change in its state of motion. The principle of inertia is one of the fundamental principles of classical physics which are used to describe the Motion of matter and how it is affected by applied forces....
, and animals can store elastic potential energy in their tendon
Tendon

A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension . Tendons are similar to ligaments except that ligaments join one bone to another....
s to help overcome this. Balance
Equilibrioception

Equilibrioception or sense of balance is one of the physiology senses. It helps prevent humans and animals from falling over when walking or standing still....
 is also required for movement on land. Human infant
Infant

An infant or baby is the term used to refer to the young offspring of humans....
s learn to crawl
Crawling

Crawling is a form of animal locomotion generally involving slow movement along the ground, such as that seen in snakes, snails and earthworms....
 first before they are able to stand on two feet, which requires good coordination as well as physical development. Humans are bipedal animals, standing on two feet and keeping one on the ground at all times while walking
Walking

Walking is the main form of animal locomotion on Earth, distinguished from running and crawling . When carried out in shallow waters, it is usually described as wading and when performed over a steeply rising object or an obstacle it becomes scrambling or climbing....
. When running
Running

Running is a means for an Terrestrial locomotion in animals on foot. It is defined in sporting terms as a gait in which at some point all feet are off the ground at the same time....
, only one foot is on the ground at any one time at most, and both leave the ground briefly. At higher speeds momentum
Momentum

In classical mechanics, momentum is the product of the mass and velocity of an object . For more accurate measures of momentum, see the section Momentum#Modern definitions of momentum on this page....
 helps keep the body upright, so more energy can be used in movement. The number of legs an animal has varies greatly, resulting in differences in locomotion. Many familiar mammals have four legs; insects have six, while spider
Spider

Spiders are air-breathing chelicerate arthropods that have eight legs, and chelicerae modified into fangs that inject venom. In their bodies the usual arthropod segments are fused into two Tagma , the cephalothorax and abdomen, joined by a small, cylindrical pedicel....
s have eight. Centipedes and millipedes have many sets of legs. Some have none at all, relying on other modes of locomotion.

Other animals move in terrestrial habitats without the aid of legs. Earthworm
Earthworm

Earthworm is the common name for the largest members of Oligochaeta in the phylum Annelida. The earthworm is the most known worm in America, and other countries....
s crawl by a peristalsis
Peristalsis

Peristalsis is the rhythmic contraction of smooth muscles to propel contents through the digestive tract. The word is derived from New Latin and comes from the Greek language peristaltikos, peristaltic, from peristellein, "to wrap around," and stellein, "to place."...
, the same rhythmic contractions that propel food through the digestive tract. Snakes move using several different modes of locomotion
Snake

Snakes are elongate legless carnivore reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears....
, depending upon substrate type and desired speed. Some animals even roll
Rotation in living systems

Rotation in living systems encompasses two modes of locomotion: rolling, and rotation about a fixed axle in the manner of a wheel or propeller. While many living systems terrestrial locomotion by means of rolling rotation, and despite the fact that the wheel has played an integral role in Transport of vehicles designed by humans, wheels do not ap...
, though typically not as a primary means of locomotion.

Some animals are specialized for moving on non-horizontal surfaces. One common habitat for such climbing animals
Climbing animals

There are a diverse range of climbing animals; animals that spend much of their time moving on steep, vertical, or overhanging surfaces and have appropriate adaptations for such scansorial locomotion....
 is in trees, for example the gibbon
Gibbon

Gibbons are the small apes in the family Hylobatidae. The family is divided into four genus based on their diploid chromosome number: Hylobates , Hoolock , Nomascus , and Symphalangus ....
 is specialized for arboreal
Arboreal

Arboreal is a word meaning "related to or resembling trees". Its meaning comes from the Latin arbor, meaning tree.In biology, an arboreal animal is one which inhabits or spends large amounts of time in trees or Shrubes....
 movement , traveling rapidly by brachiation
Brachiation

Brachiation is a form of arboreal locomotion in which primates swing from tree limb to tree limb using only their arms....
. Another case is animals like the snow leopard
Snow Leopard

The snow leopard , sometimes known as "ounce," is a moderately large Felidae native to the mountain ranges of Central Asia. The classification of this species has been subject to change and its exact taxonomy position is still unclear....
 living on steep rock faces such as are found in mountain
Mountain

A mountain is a landform that stretches above the surrounding land in a limited area usually in the form of a peak. A mountain is generally steeper than a hill....
s. Some light animals are able to climb up smooth sheer surfaces or hang upside down by adhesion
Adhesion

Adhesion is the tendency of certain dissimilar molecules to cling together due to attractive forces....
. Many insects can do this, though much larger animals such as gecko
Gecko

Geckos are small to average sized lizards belonging to the family Gekkonidae which are found in warm climates throughout the world. Geckos are unique among lizards in their vocalizations, making chirping sounds in social interactions with other geckos....
s can also perform similar feats.

On water
While animals like ducks can swim in water by floating, some small animals move across it without breaking through the surface. This surface locomotion takes advantage of the surface tension
Surface tension

Surface tension is an attractive property of the surface of a liquid. It is what causes the surface portion of liquid to be attracted to another surface, such as that of another portion of liquid ....
 of water. Animals that move in such a way include the water strider
Water strider

The family Gerridae contains insects commonly known as water striders, water bugs, magic bugs, pond skaters, skaters, skimmers, water scooters, water skaters, water skeeters, water skimmers or water skippers....
. Water striders have legs that are hydrophobic, preventing them from interfering with the structure of water. Another form of locomotion (in which the surface layer is broken) is used by the Basilisk lizard.

Energetics

The energetics
Bioenergetics

Bioenergetics is the subject of a field of biochemistry that concerns energy flow through living systems. This is an active area of Biology research that includes the study of thousands of different Cell processes such as cellular respiration and the many other metabolism processes that can lead to production and utilization of energy in for...
 of locomotion involves the energy expenditure by animals in moving. Energy consumed in locomotion is not available for other efforts, so animals typically have evolved to use the minimum energy possible during movement. However, in the case of certain behaviors, such as locomotion to escape a predator, performance (such as speed or maneuverability) is more crucial, and such movements may be energetically expensive. Furthermore, animals may use energetically expensive methods of locomotion when environmental conditions (such as being within a tunnel) preclude other modes.

The most common metric of energy use during locomotion is net cost of transport, defined as the calories needed above baseline metabolism to move a given distance, per unit body mass. For aerobic locomotion, most animals have a nearly constant cost of transport - moving a given distance requires the same caloric expenditure, regardless of speed. This constancy is usually accomplished by changes in gait
Gait

Gait is the pattern of movement of the limbs of terrestrial animals during locomotion. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency....
. The net cost of transport of swimming is lowest, followed by flight, with terrestrial limbed locomotion being the most expensive per unit distance. However, because of the speeds involved, flight requires the most energy per unit time. This does not mean that an animal that normally moves by running would be a more efficient swimmer, however; these comparisons assume an animal is specialized for that form of motion. Another consideration here is body mass—heavier animals, though using more total energy, require less energy per unit mass to move. Physiologists
Physiology

Physiology is the study of the mechanical, physical, and biochemical functions of living organisms. Physiology has traditionally been divided between plant physiology and animal and all living things physiology but the principles of physiology are universal, no matter what particular organism is being studied....
 generally measure energy use by the amount of oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
 consumed, or the amount of carbon dioxide
Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
 produced, in an animal's respiration
Respiration (physiology)

In animal physiology, respiration is the transport of Oxygen from the outside air to the cells within Tissue s and the transport of carbon dioxide in the opposite direction....
.

Methods used

Several diverse methods are used to study animal locomotion, addressing various different questions.

Kinematics is the study of the patterns of movement, and is usually accomplished by videotaping an animal's movement (possibly at over 2000 frames per second for high-speed movement) then digitally tracking markers placed on the animal. From this information, one can determine velocity, acceleration, joint angles, and the timing of kinematic events relative to one another, which can quantify ecologically relevant abilities (how fast an animal can run, how steep of a slope it can climb) or can aid in formulating further hypotheses about the movement.

Electromyography
Electromyography

Electromyography is a technique for evaluating and recording the activation signal of muscles. EMG is performed using an medical instrument called an electromyograph, to produce a record called an electromyogram....
 (EMG) is a method of detecting the electrical activity that occurs when muscles are activated, thus determining which muscles are used when in a given movement. This can be accomplished either by surface electrodes (usually in large animals) or implanted electrodes (often wires thinner than a human hair). Furthermore, the intensity of electrical activity can correlate to the level of muscle activity, with greater activity implying (though not definitively showing) greater force.

Force plates are platforms, usually part of a trackway, which can measure the magnitude and direction of forces of an animal's step. If used with kinematics and a sufficiently detailed model of anatomy, inverse dynamics solutions can determine the forces not just at the contact with the ground, but at each joint in the limb.

Sonomicrometry
Sonomicrometry

Sonomicrometry is the measurement of distances between targets from the differences in time of their detection in an Acoustics. Typically, Echogenicity reflectors will be embedded in a material and the material will be insonified with a transducer....
 uses a pair of peizo-electric crystals implanted in a muscle or tendon to continuously measure the length of a muscle or tendon. This is useful because surface kinematics may be off due to skin movement, and if an elastic tendon is in series with the muscle, the muscle length may not be accurately reflected by the joint angle.

Tendon force buckles measure the actual force produced by a single muscle by measuring the strain of a tendon. After the experiment, the tendon's elastic modulus is determined, and this allows scientists to determine the exact force a given muscle produces. However, this can only be used on muscles with long tendons.

Particle image velocimetry
Particle image velocimetry

Particle image velocimetry is an optical method used to obtain instantaneous velocity measurements and related properties in fluids. The fluid is seeded with tracer Particle s which, for the purposes of PIV, are generally assumed to faithfully follow the flow Dynamics ....
 is used in aquatic systems to measure the flow of fluid around and past a moving aquatic organism, allowing fluid dynamics calculations to determine pressure gradients, speeds, etc.

Fluoroscopy
Fluoroscopy

Fluoroscopy is an imaging technique commonly used by physicians to obtain real-time moving images of the internal structures of a patient through the use of a fluoroscope....
 allows real-time X-ray video, for precise kinematics of moving bones. Markers which are opaque to X-rays can allow simultaneous tracking of muscle length.

All of the methods can be combined - studies frequently combine EMG and kinematics to determine "motor pattern", the series of electrical and kinematic events which produce a given movement.

See also


  • Feather
    Feather

    Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds. They are considered the most complex integumentary structures found in vertebrates....
  • Joint
    Joint

    A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally....
  • Kinesis
    Kinesis

    Kinesis, like a taxis, is a movement or activity of a cell or an organism in response to a stimulus . However, unlike taxis, the response to the stimulus provided is non-directional....
  • Taxis
    Taxis

    A taxis is an innate behaviour response by an organism to a directional Stimulus . A taxis differs from a tropism in that the organism has motility and demonstrates guided movement towards or away from the stimulus ....


Further reading

  • McNeill Alexander, Robert. (2003) Principles of Animal Locomotion. Princeton University Press, Princeton, N.J. ISBN 0691086788


External links