Animal locomotion, which is the act of self-propulsion by an animal, has many manifestations, including running Running is a means of terrestrial locomotion allowing a human or an animal to move rapidly on foot. It is defined in human sporting terms as a gait in which at some point all feet are off the ground at the same time. This is in contrast to walking, where one foot is always in contact with the ground, the legs are kept mostly straight and the, jumping Jumping or leaping is a form of locomotion or movement in which an organism or non-living mechanical system propels itself through the air along a ballistic trajectory. Jumping can be distinguished from running, galloping and other gaits in which the entire body is temporarily airborne by the relatively long duration of the aerial phase and high and flying A number of animals have evolved aerial locomotion, either by powered flight or by gliding. Flying and gliding animals have evolved separately many times, without any single ancestor. Flight has evolved at least four times, in the insects, pterosaurs, birds, and bats. Gliding has evolved on many more occasions. Usually the development is to aid. Animals move for a variety of reasons, such as to find food, a mate, or a suitable microhabitat A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism. It is the natural environment in which an organism lives, or the physical environment that surrounds (influences and is utilized by) a species population.[citation needed], and to escape predators. For many animals the ability to move is essential to survival and, as a result, selective pressures have shaped the locomotion methods and mechanisms employed by moving organisms. For example, migratory animals that travel vast distances (such as the Arctic Tern The Arctic Tern is a seabird of the tern family Sternidae. This bird has a circumpolar breeding distribution covering the Arctic and sub-Arctic regions of Europe, Asia, and North America (as far south as Brittany and Massachusetts). The species is strongly migratory, seeing two summers each year as it migrates from its northern breeding grounds) typically have a locomotion mechanism that costs very little energy per unit distance, whereas non-migratory animals that must frequently move quickly to escape predators (such as frogs Frogs are amphibians in the order Anura , formerly referred to as Salientia (Latin salere (salio), "to jump"). Most frogs are characterized by long hind legs, a short body, webbed digits (fingers or toes), protruding eyes and the absence of a tail. Frogs are widely known as exceptional jumpers, and many of the anatomical characteristics) are likely to have costly but very fast locomotion. The study of animal locomotion is typically considered to be a sub-field of biomechanics.

Locomotion requires energy In physics, energy is a quantity that can be assigned to any particle, object, or system of objects as a consequence of its physical state. Different forms of energy include kinetic, potential, thermal, gravitational, sound, elastic and electromagnetic energy. The forms of energy are often named after a related force. German physicist Hermann von to overcome friction Friction is the force resisting the relative lateral motion of solid surfaces, fluid layers, or material elements in contact. Its colloquial opposite is slipperiness. Friction is usually subdivided into several varieties:, drag In fluid dynamics, drag refers to forces that oppose the relative motion of an object through a fluid (a liquid or gas). Drag forces act in a direction opposite to the oncoming flow velocity. Unlike other resistive forces such as dry friction, which is nearly independent of velocity, drag forces depend on velocity, inertia Inertia is the resistance of any physical object to a change in its state of motion. It is represented numerically by an object's mass. 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. Inertia comes from the Latin word, ", and gravity Gravitation, or gravity, is one of the four fundamental interactions of nature , in which objects with mass attract one another. In everyday life, gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped. Gravitation causes dispersed matter to coalesce, thus accounting for, though in many circumstances some of these factors are negligible. In terrestrial A terrestrial planet, telluric planet or rocky planet is a planet that is primarily composed of silicate rocks. Within the solar system, the terrestrial planets are the inner planets closest to the Sun. The terms are derived from Latin words for Earth , and an alternative definition would be that these are planets which are, in some notable 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 In physics, buoyancy is an upward acting force, caused by fluid pressure, that reduces an object's weight. If the object is either less dense than the liquid or is shaped appropriately (as in a boat), the force can keep the object afloat. This can occur only in a reference frame which either has a gravitational field or is accelerating due to a need not expend much energy maintaining vertical position, some will naturally sink and must expend energy to remain afloat. Drag may also present a problem in flight Flight is the process by which an object moves either through the air, or movement beyond earth's atmosphere , by generating lift, propulsive thrust or aerostatically using buoyancy, or by simple ballistic movement, and the aerodynamically Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with the difference being that gas dynamics applies to efficient body shapes of birds Birds are winged, bipedal, endothermic (warm-blooded), egg-laying, vertebrate animals. There are around 10,000 living species, making them the most varied of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.75 m (9 ft) Ostrich 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 The density of a material is defined as its mass per unit volume. The symbol of density is ρ . In some countries (for instance, in the United States), density is also defined as its weight per unit volume 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 are three physical laws that form the basis for classical mechanics. They have been expressed in several different ways over nearly three centuries, and can be summarised as follows: 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 A fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids or gas Gas is one of three classical states of matter. Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons are so energized that they leave their parent atoms (either water Water is a chemical substance with the chemical formula H2O. Its molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state, water vapor or steam or air The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night. Dry air contains roughly (by volume) 78.09% nitrogen, 20.9). ^[1] 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 or limit animal movement.

Introduction

Animals move through a variety of fluids, such as water, air and mud. Some, for example seals Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine mammals comprising the families Odobenidae (the walrus), Otariidae (eared seals, including sea lions and fur seals), and Phocidae (earless seals) and otters Otters are semi-aquatic fish-eating mammals. The otter subfamily Lutrinae forms part of the family Mustelidae, which also includes weasels, polecats, badgers, as well as others. With twelve species in seven genera, otters have an almost worldwide distribution. They mainly eat aquatic animals, predominantly fish and shellfish, but also other, 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 In fluid dynamics, drag refers to forces that oppose the relative motion of an object through a fluid (a liquid or gas). Drag forces act in a direction opposite to the oncoming flow velocity. Unlike other resistive forces such as dry friction, which is nearly independent of velocity, drag forces depend on velocity 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 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 its prey and the eventual absorption of the prey's tissue through consumption. The other main. A fusiform, torpedo 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 with, or in proximity to, a target. The term torpedo was originally used for a variety of devices, most of which would today be called mines. From about 1900 "-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 sharks Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs and many fishes A fish is any aquatic vertebrate animal that is covered with scales, and equipped with two sets of paired fins and several unpaired fins. Most fish are "cold-blooded", or ectothermic, allowing their body temperatures to vary as ambient temperatures change. Fish are abundant in most bodies of water. They can be found in nearly all aquatic, or up and down, as in marine mammals Marine mammals are a diverse group of 120 species of mammal that are primarily ocean-dwelling or depend on the ocean for food. They include the cetaceans , the sirenians (manatees and dugong), the pinnipeds (true seals, eared seals and walrus), and several otters (the sea otter and marine otter). The polar bear, while not aquatic, is also usually. Other animals, such as those from the class Cephalopoda A cephalopod (Greek plural Κεφαλόποδα ; "head-feet") is any member of the mollusc class Cephalopoda, characterized by bilateral body symmetry, a prominent head, and a modification of the mollusk foot, a muscular hydrostat, into the form of arms or tentacles. Teuthology, a branch of malacology, is the study of cephalopods. These, 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 The order Cetacea (pronounced /sɨˈteɪʃə/, L. cetus, whale, from Greek) includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek κῆτος (kētos),, 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 A fluid flowing past the surface of a body exerts a surface force on it. Lift is defined to be the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is defined to be the component of the surface force parallel to the 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 A fixed-wing aircraft, typically called an aeroplane, airplane or just plane, is an aircraft capable of flight using forward motion that generates lift as the wing moves through the air. Planes include jet engine and propeller driven vehicles propelled forward by thrust, as well as unpowered aircraft , which use thermals, or warm-air pockets to, the wings of which are also airfoils An airfoil or aerofoil (in British English) is the term that is sometimes used to refer to the shape of a manmade wing or the shape of the blades of a propeller, a helicopter rotor, or a turbine, but it is more commonly used as a synonym of wing, a helicopter rotor blade, or aerlion.. Unlike aircraft however, flying animals must be very light to achieve flight, the largest living flying animals being birds of around 20 kilograms.^[2] 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 The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, birds and bats do, and are capable of powered flight. The wings are similar in construction, due to the physical constraints imposed upon wing shape. Similarity can also be explained by shared ancestry, as evolution can only evolved at least four times, in the insects 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. Even our understanding of the aerodynamics of flexible, flapping wings and how insects fly is imperfect. The most obvious, pterosaurs Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period (220 to 65.5 million years ago). Pterosaurs are the earliest vertebrates known to have evolved powered flight. Their wings were formed by a membrane of skin, muscle, and other tissues stretching from the legs, birds Flight is the main mode of locomotion used by most of the world's bird species. Flight assists birds while feeding, breeding and avoiding predators, and bats Bats are flying mammals in the order Chiroptera . The forelimbs of bats are webbed and developed as wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums and colugos, glide rather than fly, and only for short distances. Bats do not flap. Gliding has evolved on many more occasions. The advantage gliding provides to arboreal Arboreal locomotion is the locomotion of animals in trees. In every habitat in which trees are present, animals have evolved to move in them. Some animals may only scale trees occasionally, while others are exclusively arboreal. These habitats pose numerous mechanical challenges to animals moving through them, leading to a variety of anatomical, 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 or leaping is a form of locomotion or movement in which an organism or non-living mechanical system propels itself through the air along a ballistic trajectory. Jumping can be distinguished from running, galloping and other gaits in which the entire body is temporarily airborne by the relatively long duration of the aerial phase and high, and crawling or slithering. Here friction and buoyancy are no longer an issue, but a strong skeletal In biology, a skeleton is a rigid framework that provides structure as well as protection in humans and many types of animals, particularly those of the phylum Chordata and of the superphylum Ecdysozoa. Exoskeletons are external, as is typical of many invertebrates; they enclose the soft tissues and organs of the body. Exoskeletons may undergo and muscular Muscle is the contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to produce force and cause motion. Muscles can cause framework are required in most terrestrial animals for structural support. Each step also requires much energy to overcome inertia Inertia is the resistance of any physical object to a change in its state of motion. It is represented numerically by an object's mass. 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. Inertia comes from the Latin word, ", and animals can store elastic potential energy Elastic energy is the energy which causes or is released by the elastic distortion of a solid or liquid in their tendons 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 and fascia as they are all made of collagen except that ligaments join one bone to another bone, and fascia connect muscles to other muscles. Tendons and muscles work together and can to help overcome this. Balance is also required for movement on land. Human infants learn to crawl 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. When running, only one foot is on the ground at any one time at most, and both leave the ground briefly. At higher speeds momentum 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 spiders 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. Earthworms crawl by a peristalsis, the same rhythmic contractions that propel food through the digestive tract. Snakes move using several different modes of locomotion, depending upon substrate type and desired speed. Some animals even roll, 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 is in trees, for example the gibbon is specialized for arboreal movement , traveling rapidly by brachiation. Another case is animals like the snow leopard living on steep rock faces such as are found in mountains. Some light animals are able to climb up smooth sheer surfaces or hang upside down by adhesion. Many insects can do this, though much larger animals such as geckos 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 of water. Animals that move in such a way include the water strider. 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.

Through a solid medium

Some animals move through solids such as soil by burrowing using claws, teeth, or other methods. A burrow is a hole or tunnel dug into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion. In loose solids such a sand some animals, such as the golden mole, are able to move more rapidly, 'swimming' through the loose substrate. Burrowing animals include moles, ground squirrels, naked mole rats, tilefish, mole crickets, and earthworms.

Energetics

The energetics 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. The net cost of transport of swimming is lowest, followed by flight, with terrestrial limbed locomotion being the most expensive per unit distance. ^[2] 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 generally measure energy use by the amount of oxygen consumed, or the amount of carbon dioxide produced, in an animal's respiration.^[2]

Methods of study

A variety of methods and equipment are used to study animal locomotion:

• Kinematics is the study of the motion of an entire animal or parts of its body. It is typically accomplished by placing visual markers at particular anatomical locations on the animal and then recording video of its movement. The video is often captured from multiple angles, with frame rates exceeding 2000 frames per second when capturing high speed movement. The location of each marker is determined for each video frame, and data from multiple views is integrated to give positions of each point through time. Computers are sometimes used to track the markers, although this task must often be performed manually. The kinematic data can be used to determine fundamental motion attributes such as velocity, acceleration, joint angles, and the sequencing and timing of kinematic events. These fundamental attributes can be used to quantify various higher level attributes, such as the physical abilities of the animal (e.g., its maximum running speed, how steep a slope it can climb), neural control of locomotion, gait, and responses to environmental variation. These, in turn, can aid in formulation of hypotheses about the animal or locomotion in general.

• Force plates are platforms, usually part of a trackway, that can be used to measure the magnitude and direction of forces of an animal's step. When 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.

• Electromyography (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.

• Sonomicrometry employs a pair of piezoelectric 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 inaccurate due to skin movement. Similarly, 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 force produced by a single muscle by measuring the strain of a tendon. After the experiment, the tendon's elastic modulus is determined and used to compute the exact force produced by the muscle. However, this can only be used on muscles with long tendons.

• Particle image velocimetry 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 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. For example, 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
• Joint
• Kinesis
• Taxis

References

1. ^ Bejan, Adrian; Marden, James H. (2006), "Constructing Animal Locomotion from New Thermodynamics Theory", American Scientist 94 (4): 342–349
2. ^ ^{a b c} Campbell, Neil A.; Reece, Jane B. (2005). Biology. Benjamin Cummings. ISBN 0-8053-7146-X.

Further reading

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

External links

• Unified Physics Theory Explains Animals' Running, Flying And Swimming

Categories: Locomotion | Zoology

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