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Diving

Diving

Diving has several meanings:- #Jumping or falling deliberately, often acrobatically, into water. This, and also completely unequipped swimming underwater, is described on this page. See also Underwater swimming. #Going underwater with or without breathing apparatus. When done for sport, this is sometimes called subaquatics. See:- #
- Snorkelling and free diving: swimming underwater without breathing apparatus. #
- Scuba diving and surface supplied diving: swimming or walking underwater with breathing apparatus. Humans are not the only ones to dive (in sense 1). Some species of amphibious animals such as marine mammals and some seabirds dive to catch their prey underwater. When dealing with equipment such as submarines and underwater remotely operated vehicles, the act of descending into the water is called diving and the command for the descent, especially in battle, is "dive." Scuba divers sometimes jump into water feet first from some height above the water (e.g. from a large boat or from a pier. Do not jump in head first if you are wearing any sort of scuba equipment or snorkelling equipment. In particular, an open-circuit scuba banging about on the back is big and hard and heavy and during a headfirst dive (in sense 1) may sprain or break the back or neck. Use one hand to hold your mask on. ---- Sometimes the term jumping is used to disambiguate, e.g. simply for the thrill of entering the water from a high cement tower, we might say that the children jump off the tower, to describe the airborne experience, as well as the impact with the water, but not emphasizing the dive down below the surface of the water, since the intent of jumping off the cement tower is not really to dive down under the water, and in fact the depth of diving into the water is an undesirable effect that can cause barotrauma. Ideally for recreational fun, one would like to jump from a high tower, but not dive too deep after impact.

Competitive diving

barotrauma When people dive in sense 1, they deliberately enter a body of water by jumping in, usually in a streamlined posture on entry with arms stretched forwards parallel to straightened legs and torso, typically palms-first, to create a "shadow" for the head. Competitive divers enter the water by diving from a set height above a pool. Dives are performed either from springboards, which are long flexible planks (once made of wood, now made of aluminum alloy) that bend as the divers jump on the end of the board to gain height and rotation before diving by converting potential into kinetic energy; or from rigid platforms of greater height, normally composed of concrete. In elite competition, there are two springboard height competitions, at 1 meter and 3 meters; and a platform competition at 10 meters, but in olympic competition there is only the 3 meter springboard and the 10 meter platform. Such divers may perform a variety of dives, making somersaults and twists in various orientations and from different starting positions (see Components of a Dive below). Divers are judged on whether they completed all aspects of the dive, the conformance of their body to the requirements of the nominated dive, and the amount of splash created by their entry to the water (less being better). The raw score is then multiplied by a difficulty factor, derived from the number of movements attempted. The diver with the highest total score after a sequence of dives (which depend on age group and specialty in elite competition) is declared the winner. While not a particularly popular participant sport, diving is one of the more popular Olympic sports with spectators. Much current U.S. popularity is likely due in part to the success and prominence of Greg Louganis. Successful competitors possess many of the same characteristics as gymnasts, including strength, flexibility, and kinaesthetic judgment. Synchronized diving was adopted as an Olympic sport in 2000. In this event, two divers form a team and attempt to perform identical dives simultaneously. This is an impressive spectacle, and requires great coordination between the team-mates.

Components of a Dive

A dive must be composed of one of four defined positions. They are: (1) tuck position, (2) pike position, (3) layout/straight position, and (4) free position, the latter consisting of either tuck or pike position as well as straight position in succession. The free position is generally employed in combination with twisting. There may be any multiple of half-twist rotations and half somersault revolutions combined with these positions. On the springboards, dives are performed by initially rotating from one of four starting positions: (1) forward rotation, (2)backward rotation , (3)reverse/gainer rotation , or (4)inward rotation . A forward or reverse rotating dive begins with an approach and hurdle moving along the diving board. A back or inward rotating dive begins with either a standing or rocking motion by the diver standing at the tip of the board and facing backwards. On the platforms, dives may occur in the four previously mentioned directions starting from either an upright (on foot) position or from an armstand.

Dive Scoring

Ultimately, the judges' scores given on each dive are subjective. However, there are specific rules governing how a dive is supposed to be scored. The primary factors affecting the scoring are: (1) the height of the diver at the apex of the dive, with extra height resulting in a higher score, (2) the distance of the diver from the diving apparatus throughout the dive (a diver must not be dangerously close to the board/platform, but should ideally be within 2-3 feet of it), (3) the properly defined body position of the diver according to the dive being performed, including pointed toes and knees together at all times, (4) the proper amounts of rotation and revolution upon completion of the dive and entry into the water, and (5) the amount of splash created by the diver on entry, with less splash resulting in a higher score. Each dive performed has an inherent "Degree of Difficulty." This is a numerical value in the range of about 1.0 to about 4.0 that is calculated based on an agreed-upon formula. The total score for an individual dive is determined by adding three judges' scores (e.g. the median three scores) and multiplying this sum by the degree of difficulty. The score for each dive is added to give a final score, and the diver with the highest final total is the winner of the event.

Swimming underwater and diving

The ability to dive and swim underwater can be a useful emergency skill, and is an important part of watersport and navy safety training. More generally, entering water from a height is an enjoyable leisure activity, as is underwater swimming with or without breathing apparatus.

Learning to swim underwater

Assuming that you can swim on the surface, the main obstacle to diving is likely to be the psychological barrier of immersing your head. To overcome this, try hard to keep your eyes open while under the water. Don't be afraid of water getting into your eyes; although chlorinated water can sting, it is not harmful. (Salt water is less irritating.) Your eyes, nose and ears will become accustomed to immersion; plugs and goggles are advisable when there is a risk of infection, for long periods of training, or for competitive swimming.It is important to be aware of the effect of pressure on the bodies natural air spaces. In breath-hold diving even at shallow depths it crucial to equalize your ears by blowing gently against the roof of your mouth with your mouth and nose closed allowing air to move up in to your middle ear and equalize the pressure created by immersion. The crucial step in gaining underwater mobility is adopting a suitable posture. To do this, first try to reach an object on the floor of the pool (or other body of water) that is within your depth. It will be difficult to reach from an upright posture. To get your hands to the object, jump up, bend your body well forward, throw your feet in the air, and try to reach the object, head foremost. The next exercise might be to swim a few metres towards the object on the surface, and then dive for it. It is difficult at first to get the chest below the surface; but if your legs are thrown well up in the air, their weight will force your body downwards. This is surface diving (also known as a jackknife); some snorkellers and scuba divers call it duck diving. Swimming underwater should follow quite naturally given some practice. It is largely a matter of maintaining a slightly inverted posture so as to counteract the natural buoyancy of the lungs. Strokes used in surface swimming must be adapted somewhat, and some arm movements (such as the crawl) cannot be used.

Learning to dive into water

Diving in this sense is not as difficult as it looks; again the main barrier is psychological, as diving head-first into the surface seems likely to hurt. To avoid the hurt (and possibly being knocked unconscious) the hands are usually held out (preferably palms-first) to protect the head, since fingertips-first entries often do not cast a large enough "shadow" to protect the head from a high height. Jumping in and landing hands-first tends to avoid water up the nose, but feet first often involves holding the nose. However, if going feet first, the impact often loosens the grip causing water to go up the nose, as well as resulting in one punching one's self in the mouth or otherwise the hands hitting the face on impact in addition to being dislodged from their grip. One problem in learning, is that at first there is impact that causes bruises or pain, but once learning to be streamlined, another problem arises: pain in ears. The ear pain is often absent during initial learning because lack in coordination, etc., causes the body to land in a less streamlined way, so it does not go as deep. Once streamlined, the body goes deep, resulting in immediate and tremendous pain in the ears, from the impact and sudden increase in pressure. Ear plugs seem to mitigate such pain. For safety reasons, diving should always be done into deep water and without goggles, which can damage the eyes by way of sudden increase in pressure. Most eyewear makers, such as Speedo, include instructions that advise against jumping into water with the eyewear on. However, in competitive swimming, the swimmers seem to jump off the starting blocks while wearing eyewear, which seems to run contrary to the advice of the eyewear manufacturers. Competitive swimmers wear specially designed, streamlined racing goggles which are meant to be used while diving. Competitive swimmers usually wear their goggles tighter than recreational swimmers do. This is to keep them from becoming dislodged mid-race. Competitive swimmers use a shallow racing dive which doesn't usually penetrate more than a meter into the water. There is less risk to competitive swimmers of eye injuries for these reasons. It is best to start by entering some water where the surface is close to or level with the edge. Stoop down until you are nearly double, put your hands together over your head, lean over until they nearly touch the surface, and try to glide, rather than fall, into the water. With practise the height of entry can be increased. Next, you can try taking short run, and leaping head first into the water. Some pools have increasing heights, 0 m, 1 m, 3 m, 5 m,7.5 and 10 m, but others have only limited choices. For example, the Donald Summerville pool in Toronto has only 0 m, 5 m, and 10 m heights available. This means that children learning must move from 0 m to 5 m, which is a large jump in height. At 5 m, adults who are learning often climb back down after seeing the pool from the increased height, since it looks higher from above than down below. Children, however, seem to be less afraid. Children don't seem to need to wear ear plugs, or have as much problems with pain. This may be due to the volume to surface area ratio, e.g. an adult who is twice the height of a child will be eight times as heavy, but present only four times the surface area (volume varies as cube of height; surface area as square of height), resulting in deeper penetration of the water. Perhaps there is also the effect of muscles and bones having a strength that varies as the square of the length, and volume as the cube; this is why ants can fall from great heights with less damage. Therefore, it is much more difficult to learn in adulthood, if one does not learn as a child. To make a clean entry, you should keep your body, arms, and legs quite stiff, and in a straight line. Tuck your head in so that your hands break the surface in front of it.

Feet first or hands first

Hands first results in more streamlined entry, and less pain, if things work out correctly, but since the body needs to change orientation 180 degrees, things can go wrong, such as having legs bent, resulting in bruised thighs. The bruises that swell up usually go away after about 14 days or so. Once getting streamlined, then ears will hurt. Feet first is less streamlined, and also the nose is facing the "wrong" way, and water is blasted up the nose. To avoid this, one hand may be used to hold the nose. Usually the hand will be pulled off, unless it is tucked in tight. Using the other arm to hold the first arm in tight helps in this regard, since the outer arm gets yanked away at time of impact, but the inner arm sometimes remains holding the nose. Crossing the legs when going feet first tends to reduce the effective impact on the genitalia, which might otherwise be felt as referred pain in the abdomen. When going feet first there is a choice in pointing the toes, more or less. More pointed (streamlined) impacts further up (genitalia, nose, etc.), and not pointed helps to bear the brunt of the water on the feet, which are often hard and calloused from walking barefoot on gravel roads. Sometimes people wear shoes if doing feet-first entries from large heights. If going hands first, it is important to keep arms out to protect the head. Looking down at the water will likely result in a badly bruised face, but some people take that risk and quickly pull the head in just before impact. When doing so, a common mistake is to overshoot, and to pull the head in too far, bruising the top of the head. Thus it seems easiest to keep the head steady, and also this allows the shoulders to be brought in to help protect the ears when the arms are extended. Fingers should not be interlocked, or they may be broken or damaged. The most recommended way is to grab one wrist with the other hand and quickly separate the arms under water. There are several benefits to this method, such a reduction of impact speed felt by the rest of the body (less injuries), dispersion of local surface tension (less injuries, pain, splash), reduced splash and most importantly protection for the head. A good streamlined entry results in less sudden energy transfer/dissipation, and therefore less pain and bruising, except on the palms which are usually tough enough to withstand the approximately 300 pounds (136 kg) or so of impact force from a height of 10 meters (approximately 14 pounds per square inch of water column). One non-standard diving (class 1) method sometimes seen is entering the water in the fetal position bottom first, making a big splash. This is sometimes called bombing. If done from excessive height, there is a risk of the impact pressure pumping water into the anus. It also may wet people standing beside the pool. Blunt entries of this sort will also result in bruising, if done from any but the lowest towers. Another undesired entry attitude is the bellyflop. In it, the body enters the water horizontally or nearly so, belly down.

The effect of height on the dive

The following table summarizes velocity of impact, and time-in-the-air, from the various standard heights of 1 m, 3 m, 5 m, and 10 m, that are found in municipal swimming baths, as well as from greater heights. The impact velocity and time of impact vary as the square root of the height. Heights beyond 10 m are not commonly found at municipal swimming baths, but exist at "use at your own risk" places such as bridges and cliffs. Cliff jumping, a common pastime for daredevil children, often takes place at heights of 20 m to 30 m. There is a limit to how high one can jump from and survive, regardless of water depth. For example, the Golden Gate Bridge is 220 feet (66 m) high and overlooks water deep enough to not hit the bottom, but the result is (almost) certain death. Thus the 66 m jump listed below is only used for suicide, but the other heights are typical of recreational bathing. Although 66 m is a "lethal dose", children often jump from 30 m (approximately 50% lethal dose) for recreation. This can be quite dangerous (e.g. if landing badly, or hitting a branch or dead fish or other object floating on the surface). The impact can also knock him unconscious, and, in absence of lifeguards (i.e. bridge jumping or cliff jumping), can cause drowning, even if from less than the lethal height. There have been documented accounts of people walking away from dives as high as 54 m, as well as the occasional Golden Gate Bridge survivor. A risk associated with very high dives is compression of the spine, often resulting in paralysis, which happens when the feet decelerate sooner than the upper body. One should note that in heights above 30 m, there is little additional time in the air, yet the velocity upon impact increases considerably. Thus, diving from heights above 30 m offers no advantage for acrobatics or thrill-seeking, but instead greatly increases the risk of injury. Category:Diving Category:Olympic sports Category:Individual sports ja:ダイビング

Acrobatics

Acrobatics (from Greek Akros, high and bat, walking) is one of the performing arts. Acrobatics involves difficult feats of balance, agility, and coordination. Most things in this athletic category need a lot practice to do, and often need to be worked up to, doing similar but easier versions of the act first before trying the end result. performing arts
- aerial tissu
- juggling
- trapeze work
- wire-walking
- contortion
- pole climbing
- springboard diving
- tower diving
- adagio
- acrobalance
- Corde lisse
- Spanish web Gymnastics is a sport that shares many aspects with acrobatics. Category:Arts Category:performing arts Category:Circus skills

Underwater

:For other uses of the word underwater, see Underwater (disambiguation) Underwater (disambiguation) Underwater, sometimes shortened as U/W, is a term describing the realm below the surface of water where the water exists in a natural feature (called a body of water) such as an ocean, sea, lake, pond, or river. Three quarters of the planet earth is covered by water. A majority of the planet's solid surface is abyssal plain, at depths between 4000 and 5500 m (13,000 to 18,000 ft) below the surface of the oceans. The solid surface location on the planet closest to the center of the orb is the Challenger Deep, located in the Mariana Trench at a depth of 10,924 m (35,838 ft) under the sea. Although a number of human activities are conducted underwater—such as scuba diving for work or recreation, or even underwater warfare with submarines—this very extensive environment on planet earth is hostile to humans in many ways and therefore little explored. An immediate obstacle to human activity under water is the fact that human lungs cannot naturally function in this environment. Unlike the gills of fish, human lungs are adapted to the exchange of gases at atmospheric pressure, not liquids. Aside from simply having insufficient musculature to rapidly move water in and out of the lungs, a more significant problem for all air breathing animals, such as mammals and birds, is that water contains so little dissolved oxygen compared with atmospheric air. Air is around 21% O₂; water typically is less than 0.001% dissolved oxygen. The density of water also causes problems that increase dramatically with depth. The air pressure at the planet surface is 101 kilopascals (14.7 lb. per sq. inch). A comparable water pressure occurs at a depth of only 10 m (34 ft.) (9.8 m (33 ft) for sea water) Thus, at about 10 m below the surface the water exerts twice the pressure (2 atmospheres or 200 kPa absolute) on the body as air at surface level. For solid objects like our bones and muscles, this added pressure is not much of a problem; but it is a problem for any air-filled spaces like the mouth, ears, paranasal sinuses and lungs. This is because the air in those spaces reduces in volume when under pressure and so does not provide those spaces with support from the higher outside pressure. Even at a depth of 8 feet (2.5 m) underwater, an inability to equalize air pressure in the middle ear with outside water pressure can cause pain, and the tympanic membrane can rupture at depths under 10 ft (3 m). The danger of pressure damage is greatest in shallow water because the rate of pressure change is greatest at the surface of the water. For example the pressure increase between the surface and 10 m (33 ft) is 100% (100 kPa to 200 kPa), but the pressure increase from 30 m (100 ft) to 40 m (130 ft) is only 25% (400 kPa to 500 kPa). Any object immersed in water is provided with a buoyant force that counters the force of gravity, appearing to make the object less heavy. If the overall density of the object exceeds the density of water, the object sinks. If the overall density is less than the density of water, the object rises until it floats on the surface.gravity)]] With increasing depth underwater, sunlight is absorbed, and the amount of visible light diminishes. Because absorption is greater for long wavelengths (red end of the visible spectrum) than for short wavelengths (blue end of the visible spectrum), the colour spectrum is rapidly altered with increasing depth. White objects at the surface appear bluish underwater, and red objects appear dark, even black. Although light penetration will be less if water is turbid, in the very clear water of the open ocean less than 25% of the surface light reaches a depth of 10 m (33 feet). At 100 m (330 ft) the light present from the sun is about 0.5% of that at the surface. The euphotic depth is the depth at which light intensity falls to 1% of the value at the surface. This depth is dependent upon water clarity, being only a few meters underwater in a turbid estuary, but may reach 200 meters in the open ocean. At the euphotic depth, plants (such as phytoplankton) have no net energy gain from photosynthesis and thus cannot grow. At depths greater than a few hundred meters, the sun has little effect on water temperature, because the sun's energy has been absorbed by water at the surface. In the great depths of the ocean the water temperature is very cold. In fact, 75% of the water in the world ocean (the great depths) has a temperature between 0 °C and 2 °C. Water conducts heat around twenty five times more efficiently than air. Hypothermia, a potentially fatal condition, occurs when the human body's core temperature falls below 35 °C. Insulating the body's warmth from water is the main purpose of diving suits and exposure suits when used in water temperatures below 25 °C. Sound is transmitted about four times faster in water (1435 m/s) than it is in air (330 m/s). The human brain can determine the direction of sound in air by detecting small differences in the time it takes for sound waves in air to reach each of the two ears. For these reasons divers find it difficult to determine the direction of sound underwater.
- See also: Timeline of underwater technology

References

- Dueker, C. W. 1970, Medical aspects of sport diving. A.S. Barnes and Co., New York. 232 pp.
- [http://geosun1.sjsu.edu/~dreed/105/exped6/1.html The Briny Deep] – Oceanography notes at San Jose State University. Category:Diving Category:Oceanography Category:Environments

Snorkelling

Snorkeling is the practice of swimming at the surface of a body of water equipped with a mask and a short tube called a snorkel. It is a popular recreational activity, particularly at tropical resort destinations. Since snorkeling requires calm water (where there are no waves to splash into the snorkel), it is typically done in protected areas, such as lagoons. Snorkeling requires no special training, only the ability to swim and to breathe through the snorkel. However, it can be helpful to know how to expel water from the snorkel following a dive below the surface, which may allow water to enter the snorkel. The mask and snorkel are similar to those used in scuba diving, but since they are not subjected to the pressures of deep water, they can be more lightweight and comfortable. The primary attraction of snorkeling is the opportunity to observe underwater life in a natural setting. This may include coral reefs and their denizens, such as fish, octopuses, starfish, sea urchins, and mollusks. Snorkeling in sandy areas may allow sighting of rays and various flatfish. Other organisms that can be seen while snorkeling include various forms of seaweed, such as kelp; jellyfish; and sea turtles.

Popular snorkeling locations

- Hawaiian islands
- Caribbean
- Galapagos islands

Sources

Snorkelling for All, BSAC, ISBN 0091883040

External links

- [http://www.bsacsnorkelling.co.uk British Sub-Aqua Club - BSAC Snorkeling]

Swimming

Swimming is the method by which living creatures move themselves through water in a method not involving simply walking on the bottom. Swimming is a popular recreational activity and a competitive sport. There are many health benefits of swimming, but it also entails risks if basic precautions are not taken. water water

Technique

The human body is composed primarily of water, and thus has a very similar density. But since only roughly 70% of the body is water, it is slightly less dense than the surrounding water, which exerts a buoyant force on it. Thus, staying afloat requires only a slight propelling of water downward relative to the body, and transverse motion only a slight propelling of water in a direction opposite to the direction of intended motion, due to generally low hydrodynamic drag. This propelling is typically accomplished by cupping the hands and using them as paddles, and by kicking the legs to push water away from the body. With practice, technique can convert a slow or average swimmer to at least a moderately fast swimmer. Since speed converts directly into distance, the same techniques that improve speed also aid one to move farther with the same effort. The torso and the legs should be kept as much as possible parallel to the surface of the water. Dropped legs or a slanted torso dramatically increase drag. The hand should be extended forward of the head, as much as possible. This increases the average length at the water-line, substantially increasing speed. This is an effect long used by boat designers, and unconsciously used by "naturally good swimmers." The time spent on the side should be maximized because the torso is smaller front-to-back than side-to-side on most swimmers. This reduces the frontal cross-section, reducing drag further, and also increasing the ratio between the body's water-line-length and width. Similar improvements are possible by orienting the narrowest direction of head, hands, legs and arms into the water. The torso is by far the most critical. The motion of the hand, arm, and leg from back to the front should be in the air as much as possible, and in the water, oriented as perfectly as possible, because the returning appendage has to move at least twice as fast as the swimmer, and in the water generates eight times the drag (drag increases with the cube of the speed) of an equal amount of torso frontal area. The basic "catch" of the water is not nearly as critical as the above items. Most swimmers simply grab water with their hand flat, or the fingers slightly spread, and then draw it smoothly down their body. None of the above techniques require improved strength. With strength training, the hands and feet can be extended further into the water, gaining more propulsion. For beginners, increased strength brings only small improvements if the above strategies (minimising drag and lengthening water-line) are not optimal. A number of swimming styles have been developed based on the implementation of some or all of these principles. The 500 yard freestyle and the 200 yard freestyle are considered to be the best events in swimming, though the 50 yard freestyle is considered the hardest.

History

Main article: History of swimming Swimming has been known since prehistoric times. Drawings from the stone age were found in "the cave of swimmers" near Wadi Sora (or Sura) in the southwestern part of Egypt. Written references date back up to 2000 B.C., including Gilgamesh, the Iliad, the Odyssey, the Bible (Ezekiel 47:5, Acts 27:42, Isaiah 25:11), Beowulf, and other sagas. In 1538 Nicolas Wynman, German professor of languages, wrote the first swimming book "Colymbetes". Competitive swimming in Europe started around 1800, mostly using breaststroke. The front crawl, then called the trudgen was introduced in 1873 by John Arthur Trudgen, copying it from Native Americans. Swimming was part of the first modern Olympic games in 1896 in Athens. In 1902 the trudgen was improved by Richard Cavill, using the flutter kick. In 1908, the world swimming association Federation Internationale de Natation (FINA) was formed. Butterfly was first a variant of Breaststroke, until it was accepted as a separate style in 1952.

Competitive swimming

Competitive swimming is swimming with the goal to maximize performance, usually the speed of swimming. Competitive swimming became popular in the 19th century, and is an event at the Summer Olympic Games. Competitive swimming's international governing body is FINA, which includes local sub groups such as USA Swimming (USAS) and United States Masters Swimming (USMS) in the United States, Amateur Swimming Association (ASA) and Swimming Teachers Association (STA) in the United Kingdom. FINA regulates four swimming disciplines, swum over different distances.
- Freestyle refers to "any style", and in competitive swimming places no restrictions on what action the competitors use, except during the freestyle portion of medley swimming. In practice, almost all freestyle events are swum using front crawl. Events are held at distances of 50 m, 100 m, 200 m, 400 m, 800 m and 1500 m. Events are held in yards at distances of 50 y, 100 y, 200 y, 500 y, 1000 y, and 1650 y.
- Butterfly events require that the swimmer's actions retain bilateral symmetry (the left side of the body has to do the same as the right). It is commonly considered the most physically challenging of the strokes. Events are held at distances of 50 m, 100 m, and 200 m. Events are also held in yards.
- Breaststroke, from which the butterfly stroke evolved, places the additional restriction that the swimmer's hands must be pushed forward together from the breast and that the elbows must remain under the water. It is the slowest stroke in competitive swimming. Events are held at distances of 50 m, 100 m, and 200 m. This stroke, as well as butterfly requires great shoulder strength. Events are also held in yards.
- Backstroke places no symmetry restrictions, but swimmers must lie on their back at all times except during turns to perform the stroke. Backstroke is performed, in essence, as an inversion of the crawl — competitors swing their arms back over their shoulder, alternately, and pull through under the water to provide motive power, with a flutter kick. Events are held at distances of 50 m, 100 m, and 200 m. Events are also held in yards. In the US all distances are swum in short course yards for NCAA and high school competition, except during Olympic years in which the NCAA championships are held in the short course meters format. Short course means that each length is 25 yards or meters. There are also world championships held in the short course meters format, however, it is not as publicised as the traditional long course (50 meters per length) world championships. The Olympic Games are competed exclusively in the long course meters format. World Championships are held each year, including both the traditional long course meters format and the less popular short course meters format. World records are tabulated separately for each event in both formats; world records are not recognized for the short course yards format. Backstroke and Freestyle are referred to as "long-axis" strokes because the body is in a much longer position than when performing breaststroke or butterfly, which are known as "short-axis" strokes. In addition to that there are a number of combination events in competitive swimming.
- Relay, where a number of swimmers swim sequentially. Events are held at distances of 4×50 m freestyle, 4×100 m freestyle and 4×200 m freestyle.
- Individual Medley, where one swimmer swims Butterfly, Backstroke, Breaststroke, and Freestyle in this order. Events are held at distances of 100 m (short course 25 m pools only), 200 m, and 400 m.
- Medley Relay, where four swimmers swim Backstroke, Breaststroke, Butterfly, and Freestyle in this order. Events are held at distances of 4×50 m medley and 4×100 m medley. Full rules are on the [http://www.fina.org/swimrules.html rules web page] of FINA. Competitive swimming has traditionally been dominated by the United States, but recently that dominance has been challenged by Australia , where swimming is a hugely popular recreational activity, and participant and spectator sport. The success of Australian swimmers like Ian Thorpe, Michael Klim, Grant Hackett, and Kieren Perkins is reminiscent of Australia's previous golden age of swimming in the 1950s and 1960s, which saw the emergence of swimmers such as Shane Gould and Dawn Fraser. However, American swimmers, led by Michael Phelps, Natalie Coughlin, Kaitlin Sandeno, and Brendan Hansen have been holding off the Australians just like they did in the 2004 Olympics. Other countries with a great tradition in swimming are Russia (former Soviet Union: as to recent times, Alexander Popov was prominent in the fast races in the 1990s), Hungary, Poland, Germany, China (which has had a history of controversy due to probable steriod use), and Sweden. Newbies which recently had scored relevant success include Italy and Japan. There are also a number of other competitive swimming performances, for example a long distance 5 kilometer open-water event, which became part of the Olympic program in 2000, or long distance swims across the English Channel, or circumnavigating Manhattan Island. The world record for the longest nonstop swim is held by Martin Strel for swimming 504km nonstop in 2001 in the Danube River. He also swam the Mississippi River in 2002 in 66+2days, a total of 3885km. The current holder of the most world records for long distance swimming is Vicki Keith. Swimming is also a crucial part of other sports, such as water polo, synchronized swimming, modern pentathlon and triathlon. (See List of water sports)

Championships

- Swimming at the Summer Olympics (include swimming, water polo, diving and synchronised swimming)
- World Aquatics Championships (include swimming, water polo, diving and synchronised swimming)
- FINA Long Course World Championships
- FINA Short Course World Championships
- Pan Pacific Swimming Championships

Recreational swimming

Pan Pacific Swimming Championships The most common reason for swimming is probably recreation, where the swimmer enters the water merely for enjoyment. Many swimming styles are suitable for recreational swimming. Most recreational swimmers prefer a style that keeps their head out of the water and uses an underwater arm recovery, for example breaststroke, side stroke, or 'dog paddle', however, out-of-water recovery of freestyle or butterfly gives rise to better exploitation of the difference in viscosity of the two media (air and water). Butterfly, which consists of out-of-water recovery with even symmetry in body movements, is most suited to rough water swimming. For example, Vicki Keith crossed the rough waters of Lake Ontario using butterfly. Much of recreational swimming takes place in pools, where the water is calm. Therefore freestyle (which does not work as well in rough water) is suitable. However, playing around in rough water is a common source of recreation, but is sometimes dangerous due to undertow or the risk of injury from rocks on the bottom of a lake or riverbed. Swimming pools are popular venues for recreational swimming, as are beaches, lakes, swimming holes, creeks, rivers, and sometimes canals.

Occupational swimming

A number of people enter the water and swim as part of their work. For example, abalone divers or pearl divers swim and dive to obtain an economic benefit, as do spear fishermen. Swimming is used to rescue other swimmers in distress. There are a number of specialized swimming styles specially for rescue purposes (see List of swimming styles). Such techniques are studied for example by lifeguards, or members of the Coast Guard. The training of these techniques also evolved into competitions, as for example surf lifesaving. Swimming is also done for scientific research. Swimming is studied to improve the swimming performances of competitive swimmers. Swimming is also used in marine biology to observe plants and animals in their natural habitat. Other sciences may also use swimming. Konrad Lorenz for example swam with geese as part of his studies of animal behavior. Swimming also has military purposes besides the mere need to cross waters. A swimmer in the water or under the water can be difficult to detect, especially at night. Military swimming is usually done by Special forces, as for example Navy SEALS. Swimming is used to approach a location, gather intelligence, sabotage, or combat, and to depart a location. This may also include airborne insertion into water or leaving a submerged submarine through a hatch or the torpedo tubes. Special equipment and techniques are also used to engage hostiles in and under water. Swimming more recently has become a professional sport as well. Companies such as Speedo and Tyr Sports, Inc. sponsor swimmers just as Nike might sign contracts with basketball players. Also cash awards are given at many of the major competitions for breaking records. An example of a professional swimmer is Michael Phelps who has a contract with Speedo.

Swimming for exercise

Speedo Swimming is a good form of exercise. Because the density of the human body is approximately similar to that of water, the body is supported by the water and less stress is therefore placed on joints and bones. Furthermore, the resistance against movement depends heavily on the speed of the movement, allowing the fine tuning of the exercise according to one's ability. Therefore, swimming is frequently used as an exercise in rehabilitation after injuries, or for the disabled. Resistance swimming is one form of swimming exercise. It is done either for training purposes, to hold the swimmer in place for stroke analysis, or to enable one to swim in a confined space for either athletic or therapeutic reasons. Resistance swimming can be done either against a stream of water set in motion by a (usually) self-contained mechanical device (often termed a swimming machine) or by holding the swimmer stationary by means of elastic attachments. Swimming is an aerobic exercise due to the relatively long exercise time, requiring a constant oxygen supply to the muscles, except for short sprints where the muscles work anaerobically. As with most aerobic exercise it is believed to reduce the harmful effects of stress. While aerobic exercises usually burn fat and help with losing weight, this effect is limited in swimming, even though being in cold water burns more food energy to maintain body temperature. The reason that swimming does not significantly reduce weight is still poorly understood, but seems to be related to the better heat conduction of water. A number of reasons are suspected.
- First, water cools the body much faster than air, and most researchers believe that subsequently the body aims to maintain a layer of fat under the skin for insulation.
- Secondly, it is believed that appetite decreases as your body temperature increases, as for example during exercise. However, during swimming the body is cooled down almost instantly as the surrounding water is usually cooler than the body temperature, and some researchers believe that this may actually increase the appetite. This assumption is not yet proven by research.
- Thirdly, fast swimming requires a high level of effort, meaning glycogen rather than fat is burned. Prolonged exercise at lower intensity is better for fat-burning.
- Finally, some researchers also believe that the metabolism of the body increases at higher body temperature, burning more food energy. Again, during swimming the body is cooled down by the surrounding water, reducing the metabolism, and subsequently the amount of food energy burnt. This assumption is also not yet proven by research. Swimming exercises almost all muscles in the body. Usually, the arms and upper body are exercised more than the legs. In competitive swimming, excessive leg muscles can be seen as a disadvantage as they consume more oxygen, which would be needed for the muscles of the arms. However, this depends on the swimming style. While breaststroke generates significant movement with the legs, front crawl propels the body mainly with the arms. Sometimes the swimming consists of swimming laps using a conventional stroke, such as the front crawl; other forms can include different forms of exercise performed in the water, such as water aerobics.

Health risks

Swimming is considered a sport with a low risk of injury. Nevertheless there are some health risks with swimming. Most lethal risks in swimming are due to the inability to swim. It is recommended to swim in an area supervised by lifeguards and to pay attention to the water conditions. Possible health risks, ranging from potentially lethal to minor temporary inconveniences, are listed below:
- Drowning can cause injury or death.
- Drowning due to adverse water conditions which may force the body under water or force water into the body.
- Drowning due to negative buoyancy, for example due to being attached to items heavier than water, e.g. medieval armour or a concrete block around the feet, or being trapped in an item heavier than water, e.g. a sinking ship.
- Drowning due to outside influence, as for example being pushed under water by another person by accident or intentionally.
- Drowning can also be caused by the inability to swim due to exhaustion or unconsciousness or a combination thereof. Besides other health risks listed below this may be due to effects unrelated to swimming as for example heart attacks and other strokes.
- Risks due to the effect of water on the human body.
- Secondary drowning, where inhaled salt water in the lungs after a near drowning starts to create a foam in the lungs that restricts breathing.
- Thermal shock after jumping into water can cause the heart to stop.
- Spending time in the water can give a wrinkled skin on the fingers, palms of the hands, and the soles of the feet. This disappears quickly without any negative effect.
- Injuries may heal slower if submerged in water.
- Risks due to chemicals in the water.
- In chlorinated swimming pools the chlorine may burn in the eyes. This stops shortly after leaving the water. Other disinfection techniques using, for example, ozone can avoid this effect.
- Breathing small quantities of chlorine from the water surface whilst swimming for long periods of time may have an adverse effect on the lungs.
- Chlorine also has a negative cosmetic effect on hair after repeated long exposure.
- Risks due to bacteria, fungi and viruses in the water. Water is an excellent environment for many bacteria, which may affect humans. The risk and severity of infection vary with the water quality. A selection of more common infections related to swimming are:
- Swimming and showering can cause athlete's foot (boat bug). The easiest way to avoid this is drying the space between the toes after swimming.
- Swimming can cause ear infections in the ear canal (Otitis externa).
- Cases of Legionnaires' disease have been transmitted by improperly sterilized showers after swimming. Good swimming facilities heat the shower water to 60°C (140°F) once per week during closing time to disinfect the water system.
- There is no known case of transmission of AIDS through the water.
- There is no known case of pregnancy due to sperm transported through the water while swimming.
- Risks due to physical activity in the water specific to swimming.
- Competitive swimmers may have a health risk due to overuse. Butterfly swimmers for example may develop some back pain and shoulder pain after long years of training, breaststroke swimmers may develop knee pain, and front crawl and backstroke swimmers may develop shoulder pain.
- Long term swimmers may occasionally get some abnormal growth in the ear canal due to the frequent splashing of water in the ear canal.
- Shallow water blackout is a condition where holding the breath causes a sudden unconsciousness due to oxygen starvation (Asphyxia).
- Exhaustion due to long swims or bad physical shape can cause drowning.
- Risks due to water and weather conditions.
- An outdoor swimmer can be hit by lightning during a thunderstorm. Lightning will usually hit the highest point available, as for example the head of a swimmer on a flat water surface.
- Strong winds can cause waves and can blow a swimmer away from land.
- Hypothermia due to cold water can cause rapid exhaustion and unconsciousness depending on the water temperature and the body conditions.
- Currents, including tides and rivers can cause exhaustion and can move a swimmer away from safety or pull swimmers under water.
- Due to the reflections in the water, the effect of the sun is more severe than on land, causing sunburn. Furthermore, swimming is usually done while exposing most of the body to sunlight, especially some areas usually covered (around the rims of the bathing suit) or in the shade (the back of the knees). In the long term this may increase the risk of cancer and decrease the aesthetics of the skin.
- Risks due to other objects in the water.
- A collision with another swimmer or other object as for example the wall of a pool, rocks, and boats, especially the propellers thereof, may result in injuries. Severe injuries are possible after hitting an object while diving into the water. Injuries can also be caused by stepping on sharp objects, e.g. broken glass.
- Dangerous marine life can attack swimmers in self defense or for prey, often in combination with a poison.
- Marine life that sting, e.g. jellyfish and some corals.
- Marine life that pierce, e.g. sea urchins.
- Marine life that bites, e.g. sharks and other fish, snakes, or lobster and crabs.

Clothing

The desire or cultural demand of modesty together with the awkwardness or unsuitability of conventional clothing in the water led to the development of the swimsuit (and in Victorian times, the bathing machine). Men's swimsuits tend to be trunks, surf or boardshorts, competition briefs, cut-offs, or jeans. Women's swimsuits are generally either one-piece swimsuits of traditional or competitive style (such as the racerback) or bikinis. Also there is the monokini, in case the coverage of the breasts is neither required nor desired. Bodyskins are special whole body swimsuits for competitive swimming, designed to reduce skin drag. (See Competitive swimwear) Swimwear manufacturers/suppliers include Speedo, Tyr Sports, Inc., Arena, Nike, Inc., and Adidas. Nude swimming is done:
- at nudist areas
- in Denmark, all beaches are clothing-optional unless marked otherwise
- during nudist hours in some swimming pools
- at (usually small) swimming pools in saunas
- without being formally allowed, at quiet places and hours; also called skinny dipping
- at private swimming pools and beaches, not visible to outsiders

Historical Bibliography

- Maniscalco F., Il nuoto nel mondo greco romano, Naples 1993.
- Mehl H., Antike Schwimmkunst, Munchen 1927.

Scuba diving

Scuba diving is the use of independent breathing equipment to stay underwater for long periods of time for recreational diving and professional diving. Generally the diver swims underwater, but walking and the use of diver propulsion vehicles is possible while breathing from scuba equipment. The word 'SCUBA' is an acronym for "Self Contained Underwater Breathing Apparatus", but it is grammatically acceptable to refer to 'scuba equipment' or 'scuba apparatus' in conversation. The two types of scuba equipment are the "open-circuit" Aqua-lung, developed by Jacques-Yves Cousteau and the "closed-circuit" rebreather.

History of diving

Men and women have practiced breath-hold diving for centuries. Indirect evidence comes from ancient artifacts of undersea origin found on land (e.g. mother-of-pearl ornaments), and depictions of divers in ancient drawings. In ancient Greece breath-hold divers are known to have hunted for sponges and engaged in military exploits. Of the latter, the story of Scyllis (sometimes spelled Scyllias; about 500 B.C.) is perhaps the most famous, as told by the 5th century B.C. Greek historian Herodotus (and quoted in numerous modern texts). During a naval campaign the Greek Scyllis was taken aboard ship as prisoner by the Persian King Xerxes I. When Scyllis learned that Xerxes was to attack a Greek flotilla, he seized a knife and jumped overboard. The Persians could not find him in the water and presumed he had drowned. Scyllis surfaced at night and made his way among all the ships in Xerxes's fleet, cutting each ship loose from its moorings; he used a hollow reed as snorkel to remain unobserved. Then he swam nine miles (15 kilometers) to rejoin the Greeks off Cape Artemisium. The desire to go under water has probably always existed: to hunt for food, uncover artifacts, repair ships (or sink them), and perhaps just to observe marine life. Until humans found a way to breathe underwater, however, each dive was necessarily short and frantic. One of the major hurdles of diving is to stay under water for a longer period of time. Breathing through a hollow reed allows the body to be submerged, but reeds more than two feet long do not work well; difficulty inhaling against water pressure effectively limits snorkel length. Breathing from an air-filled bag brought under water was also tried, but it failed due to rebreathing of carbon dioxide. In the 16th century people began to use diving bells supplied with air from the surface, the first effective means of staying under water for any length of time. The bell was held stationary a few feet from the surface, its bottom open to water and its top portion containing air compressed by the water pressure. A diver standing upright would have his head in the air. He could leave the bell for a minute or two to collect sponges or explore the bottom, then return for a short while until air in the bell was no longer breathable. In 16th century England and France, full diving suits made of leather were used to depths of 60 feet. Air was pumped down from the surface with the aid of manual pumps. Soon helmets were made of metal to withstand even greater water pressure and divers went deeper. By the 1830s the surface-supplied air helmet was perfected well enough to allow extensive salvage work. Starting in the 19th century, two main avenues of investigation one scientific, the other technologic - greatly accelerated underwater exploration. Scientific research was advanced by the work of Paul Bert and John Scott Haldane, from France and Scotland, respectively. Their studies helped explain effects of water pressure on the body, and also define safe limits for compressed air diving. At the same time, improvements in technology - compressed air pumps, carbon dioxide scrubbers, regulators, etc., - made it possible for people to stay underwater for long periods. Used with permission from Lawrence Martin, M.D. Web Site of Origin: [http://www.lakesidepress.com/abcindex.htm www.lakesidepress.com/abcindex.htm]. The web pages containing the scuba book are inoperative at present, and have not yet been moved to a new site. The above URL is the global or index web site. And see Timeline of underwater technology.

Diving Issues

See Diving hazards and precautions.

Equipment to allow underwater breathing

The two most common types of equipment are:
- surface supplied diving, where the diver's breathing gas (usually air) is pumped down from the surface. Standard diving dress is a historically interesting type of surface supplied diving equipment.
- scuba, where the breathing gas supply is carried by the diver.

Need to see underwater

Diving masks and diving helmets solve this problem. Occasionally commando frogmen use special contact lenses instead.

Avoiding losing body heat

Water conducts heat from the diver 25 times better than air, which can lead to hypothermia. Except in very warm water, the diver needs the thermal insulation provided by wetsuits and drysuits. See the main article: Diving suit.

Avoiding skin cuts and grazes

Diving suits also help prevent the diver's skin being damaged by rough or sharp underwater objects and marine animals and coral.

Diving longer and deeper safely

There are a number of techniques to increase the diver's ability dive deeper and longer:
- technical diving - Diving Deeper than 130 feet and/or using mixed gases.
- surface supplied diving - use of umbilical gas supply and diving helmets
- saturation diving - long-term use of underwater habitats under pressure and a gradual release of pressure, over several days, in a decompression chamber at the end of a dive

Being mobile underwater

- The diver needs to be mobile underwater. Personal mobility is enhanced by fins worn on the feet and Diver Propulsion Vehicles. Other equipment to improve mobility includes diving bells and diving shots.

Sources

The Diving Manual, BSAC, ISBN 095389192534 Dive Leading, BSAC, ISBN 0953891941 The Club 1953-2003, BSAC, ISBN 095389195X

External links

-
- [http://www.sportdiver.com Sport Diver] - Dive magazine covering dive travel adventures, scuba diving gear reviews, and PADI Diving Society events & news. Official magazine of the PADI Diving Society.
- [http://www.fishid.com/ marine life learning center] - Marine Life identification and behavior books.
- [http://www.diversalertnetwork.org/ Divers Alert Network]
- [http://www.bsac.com British Sub-Aqua Club] - BSAC Welcome
- [http://scuba.rinkes.nl/ Brief history of diving] - From antiquity to the present.
- [http://www.scuba-guide.com Scuba Diving Guide] - Information for scuba divers.
- [http://www.thescubaguide.com The Scuba Guide] - Massive directory of gear and articles for beginning scuba divers.
- [http://www.scubamonster.com/Uwe/ForumList.aspx Scuba Monster] - Scuba Usenet discussions and archive.
- [http://www.nauiww.org/ NAUI Worldwide] is the world's oldest not-for-profit membership training agency organized solely to support and promote dive safety through education.
- [http://www.padi.com PADI International] - Professional Association of Diving Instructors.
- [http://www.ukdiving.co.uk UK Diving - Diving and Scuba resource] - Large Internet resource for divers. Category:Acronyms Category:Diving ms:Scuba ja:スキューバ・ダイビング

Surface supplied diving

]] Surface supplied diving refers to divers using equipment supplied with breathing gas using an umbilical cord from the surface, often from a diving support vessel but possibly, indirectly via a diving bell. SCUBA, which is commonly used in recreational diving, is the main alternative to surface supplied diving equipment. Surface supplied diving equipment and techniques are mainly used in professional diving or military diving due to the increased cost and complexity of buying and operating the equipment. This type of equipment is used in saturation diving. Divers almost always wear diving helmets or full face diving masks when being supplied from the surface. Surface supplied divers also use the spherical helmet with brass and glass windows of the historical standard diving dress. Surface supplied diving equipment usually includes communication capability with the surface, which adds to the efficiency of the working diver. The surface supplied diver is less likely to have "out-of-air" emergencies because there is more than one source of breathing gas. Category:Diving

Swimming

Technique

History

Competitive swimming

Championships

Recreational swimming

Occupational swimming

Swimming for exercise

Health risks

Clothing

Historical Bibliography

- Maniscalco F., Il nuoto nel mondo greco romano, Naples 1993.
- Mehl H., Antike Schwimmkunst, Munchen 1927.

Walking

Walking is the main form of animal locomotion on land, distinguished from running and crawling. When executed in shallow water, it is usually described as wading and when executed vertically it becomes scrambling or climbing. The word walking is derived from the Old English walcan (to roll). Walking is generally distinguished from running in that only one foot at a time leaves contact with the ground: for humans and other bipeds running begins when both feet are off the ground with each step. (This distinction has the status of a formal requirement in competitive walking events, often resulting in disqualification even at the Olympic level.) For horses and other quadrupedal species, the running gaits may be numerous, and walking keeps three feet at a time on the ground. While not strictly bipedal, several primarily bipedal human gaits (where the long bones of the arms support at most a small fraction of the bodies' weight) are generally regarded as variants of walking. These include:
- walking on crutches (usually executed by alternating between standing on both legs, and rocking forward "on the crutches" (i.e., supported under the armpits by them);
- walking with one or two canes/walking sticks, staves, or trekking poles (reducing the load on one or both legs, or supplementing the body's normal balancing mechanisms by also pushing against the ground through at least one arm that holds a long object); and
- scrambling, using the arms (and hands or some other extension to the arms) not just as a backup to normal balance, but, as when walking on talus, to achieve states of balance that would be impossible or unstable when supported solely by the legs. For humans, walking is the main form of transportation without a vehicle or riding animal. A pedestrian is a walking person, in particular on a road (if available on the sidewalk/path/pavement).

Walking as a leisure activity

sidewalk] Many people walk as a hobby, and in our post-industrial age it is often enjoyed as a form of exercise. Fitness walkers and others may use a pedometer to count their steps. The types of walking include bushwalking, racewalking, hillwalking, volksmarching, Nordic walking and hiking on long-distance paths. In some countries walking as a hobby is known as hiking (the typical North American term), rambling (a somewhat dated British expression, but remaining in use because it is enshrined in the title of the important Ramblers' Association), or tramping (the invariable term in New Zealand). Hiking is a subtype of walking, generally used to mean walking in nature areas on specially designated routes or trails, as opposed to in urban environments; however, hiking can also refer to any long-distance walk. More obscure terms for walking include "to go by Marrow-bone stage", "to ride Shank's pony" or "to go by Walker's bus." Walking in a shopping mall is often called "trolling." The average child achieves independent walking ability between 9 and 15 months old. The world's largest