Swimming describes any method by which living creatures move themselves through water apart from walking on the bottom. This article concentrates on human swimming, 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.

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.

History

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 25 m, 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 restrictions 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 metres format. Short course means that each length is 25 yards or metres. There are also world championships held in the short course metres format, however, it is not as publicised as the traditional long course (50 metres per length) world championships. The Olympic Games are competed exclusively in the long course metres format. World Championships are held each year, including both the traditional long course metres format and the less popular short course metres 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 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 3885 km by only sleeping 5 hours a day. 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)

Timing

Today swimming uses a electric touch pad to register touching the end of the lane and finishing. This was invented by Bill Parkinson of the University of Michigan, and entered use in 1957. They took a while to take over from the previous human judging, but a scandal at the 1960 Rome Olympics, when an American swimmer (Lance Larson) clearly won, but had been judged not to, resulted in an uproar and the uptake of touch pads. A discussion of the history of touch pads.

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

The most common reason for swimming is probably recreation, where the swimmer enters the water merely for enjoyment. Swimming is a good way to relax. 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

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.

Swimming may be good for asthma sufferers.

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 include the following:

• Drowning, inhalation arising from:
  • Adverse water conditions swamping or overwhelming the swimmer or causing water inhalation.
  • Negative buoyancy when attached to a heavy object or entrapment e.g. in a sinking ship.
  • Actions of others pushing under water accidentally in play or intentionally.
  • Exhaustion or unconsciousness.
  • Incapacitation through shallow water blackout, heart attacks, carotid syncope or stroke.
  • Incompetence, swimmer's ability does not meet the conditions.

• Adverse effects of immersion
  • Secondary drowning, where inhaled salt water creates a foam in the lungs that restricts breathing.
  • Salt Water Aspiration Syndrome, SWAS.
  • Thermal shock after jumping into water can cause the heart to stop.
  • Abnormal growth in the ear canal due to the frequent, long-term splashing of water into the ear canal.
  • Wrinkled skin on the fingers, palms of the hands, and the soles of the feet after long immersion; this disappears quickly without any negative effect.
  • Injuries may heal slower if submerged in water.

• Exposure to chemicals
  • Chlorine in the eyes; in chlorinated swimming pools the chlorine may burn the eyes, stopping shortly after leaving the water but may be persistent and serious. Other disinfection techniques using, for example, ozone can avoid this effect.
  • Chlorine inhalation; breathing small quantities of chlorine gas 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 after repeated long exposure, turning blonde hair green and turning teeth brown.

• Infection
  • Water is an excellent environment for many bacteria, parasites, fungi and viruses affecting humans depending on water quality.
  • Skin infections from both swimming and shower rooms can cause athlete's foot (boat bug). The easiest way to avoid this is drying the space between the toes after swimming.
  • Gastric infections, microscopic parasites such as cryptosporidium can be resistant to chlorine and can cause diarrheal illness when swimmers swallow pool water.
  • Ear infections, otitis media, (otitis externa).
  • Legionnaires' disease may have been transmitted by 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.

• Swimmers'own actions
  • Overuse injury; competitive 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.
  • Hyperventilation in a bid to extend underwater breath-hold times lowers blood carbon dioxide resulting in suppression of the urge to breath and consequent loss of consciousness towards the end of the dive, see shallow water blackout for the mechanism.

• Adverse water and weather conditions
  • Currents, including tides and rivers can cause exhaustion and can move a swimmer away from safety or pull swimmers under water.
  • Wind causes 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.
  • Lightning strike; an outdoor swimmer can be struck by lightning during a thunderstorm, it doesn't have to strike the swimmer at all, just a part of the adjacent poolstructure or boat but is attracted tothe highest point available such as the head of a swimmer.
  • Sunburn; reflections in the water can increase the severity of UV radiation exacerbated by lack of clothing protection during swimming especially those areas usually covered (around the rims of the bathing suit) or in the shade (the back of the knees. In the long term this contributes to the risk of skin cancer and disfigurement.

• Objects in the water.
  • Propellor damage is a major cause of accident, either by being run over by a boat or entaglement on climbing into a boat.
  • Collision with another swimmer, the pool walls, rocks or boats.
  • Diving into a submerged object, or the bottom, often in turbid water.
  • Snagging on underwater objects, particulary submerged branches or wrecks.
  • Stepping on sharp objects such as broken glass.

• Dangerous aquatic life
  • Stings, jellyfish and some corals.
  • Piercings, sea urchins.
  • Bites, sharks and other fish, snakes, lobster or crabs.
  • Electrocution, electric rays, electric eels.

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. Other types of swimwear include Speedos.

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