Human swimming is the self-propulsion of a person through water or another liquid, usually for the purpose of recreation, sport, exercise, or survival. Locomotion is achieved through coordinated movement of the limbs, the body, or both. Humans are able to hold their breath underwater and undertake rudimentary locomotive swimming within weeks of birth, as an evolutionary response.
Swimming is consistently found to be among the top recreational activities undertaken by the public, and in some countries, swimming lessons are a compulsory part of the educational curriculum. As a formalized sport, swimming features in a range of local, national, and international competitions, including every modern summer Olympics, which occurs every four years.
Swimming relies on the natural buoyancy of the human body. On average, the body has a relative density of 0.98 compared to water, which causes the body to float. However, buoyancy varies on the basis of both body composition and the salinity of the water. Higher levels of body fat and saltier water both lower the relative density of the body and increase its floatation.
Since the human body is only slightly less dense than water, water supports the weight of the body during swimming. As a result, swimming is "low-impact" compared to land activities such as running. The density and viscosity of water also create resistance for objects moving through the water. Swimming strokes use this resistance to create propulsion, but this same resistance also generates drag on the body.
This means that hydrodynamics are an important factor in stroke technique in terms of swimming faster, and swimmers wishing to swim faster, or wishing to tire less, will try to reduce the drag caused by the body's motion through the water. In order to be more hydrodynamic, swimmers can either increase the power of their strokes or reduce their water resistance, although increasing power to overcome resistance needs to increase by a factor of three to achieve the same effect as reducing resistance.
Efficient swimming by reducing water resistance involves having a horizontal water position, rolling the body in order to reduce the breadth of the body in the water, and extending the arms as far as possible in order to reduce wave resistance.
Human babies demonstrate an innate swimming or diving reflex from newborn until the age of approximately 6 months. Other mammals also demonstrate this phenomenon (see mammalian diving reflex). The diving response involves apnoea, reflex bradycardia, and peripheral vasoconstriction; in other words a baby immersed in water will spontaneously hold his or her breath, slow his/her heartrate, and reduce blood circulation to the extremities such as fingers and toes.
Swimming can be undertaken using a wide range of different styles, known as 'strokes,' and these strokes are used for different purposes, or to distinguish between classes in competitive swimming. It is not necessary to use a defined stroke for propulsion through the water, and untrained swimmers may use a 'doggy paddle' of arm and leg movements, similar to the way four-legged animals swim.
There are four main strokes used in competition and recreation swimming: the front crawl, the breaststroke, the backstroke and the butterfly. Competitive swimming in Europe started around 1800, mostly using the breaststroke. In 1873 John Arthur Trudgen introduced the trudgen to Western swimming competitions, after copying the front crawl used by Native Americans, but substituting a scissor kick for the traditional flutter kick in order to reduce splashing. The butterfly stroke was developed in the 1930s and was considered a variant of the breaststroke until it was accepted as a separate style in 1952.
Other strokes exist for specific purposes, such as training or rescue, and it is also possible to adapt strokes to avoid using parts of the body, either to isolate certain body parts, such as swimming with arms only or legs only to train them harder, or for use by amputees or those suffering from paralysis.
Swimming has been recorded since prehistoric times, and the earliest records of swimming date back to Stone Age paintings from around 7,000 years ago. Written references date from 2000 BC. Some of the earliest references include the Epic of Gilgamesh, the Iliad, the Odyssey, the Bible (Ezekiel 47:5, Acts 27:42, Isaiah 25:11), Beowulf, and other sagas. In 1538, Nikolaus Wynmann, a German professor of languages, wrote the first swimming book, The Swimmer or A Dialogue on the Art of Swimming (Der Schwimmer oder ein Zweigespräch über die Schwimmkunst).
There are many reasons why people swim, from swimming as a recreational pursuit to swimming as a necessary part of a job or other activity. Swimming may also be used to rehabilitate injuries, especially various cardiovascular injuries and muscle injuries.
Many swimmers swim for recreation, with swimming consistently ranking as one of the physical activities people are most likely to take part in. Recreational swimming can also be used for exercise, relaxation, or rehabilitation. The support of the water, and the reduction in impact, makes swimming accessible for people who are unable to undertake activities such as running.
Swimming is primarily a cardiovascular/aerobic exercise due to the 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, swimming is believed to reduce the harmful effects of stress. Swimming can also improve posture.
Swimming as a sport predominantly involves competition among participants to be the fastest over a given distance under self-propulsion. Different distances are swum in different levels of competition. For example, swimming has been an Olympic sport since 1896, and the current program includes events from 50m to 1500m in length, across all four main strokes and medley.
The sport is governed internationally by the Fédération Internationale de Natation (FINA), and competition pools for FINA events are 25 or 50 meters in length. In the United States of America, USA Swimming is the governing body and a pool 25 yards in length is commonly used for competition.
Other swimming and water-related sporting disciplines including diving, synchronized swimming and water polo, as well as sports which include a swimming element, such as the triathlon and the modern pentathlon.
Swimming is used to rescue people in the water who are in distress, including exhausted swimmers, non-swimmers who have accidentally entered the water, and others who have come to harm on the water. Lifeguards or volunteer lifesavers are deployed at many pools and beaches worldwide to fulfill this purpose, and they, as well as rescue swimmers, may use specific swimming styles for rescue purposes.
Swimming is also used in marine biology to observe plants and animals in their natural habitat. Other sciences use swimming, for example Konrad Lorenz swam with geese as part of his studies of animal behavior.
Swimming also has military purposes. Military swimming is usually done by special forces, such as Navy SEALs. Swimming is used to approach a location, gather intelligence, engage in sabotage or combat, and subsequently depart. This may also include airborne insertion into water or exiting a submarine while it is submerged. Due to regular exposure to large bodies of water, all recruits in the United States Navy, Marine Corps, and Coast Guard are required to complete basic swimming or water survival training.
Swimming is also a professional sport. Companies sponsor swimmers who have the skills to compete at the international level. Many swimmers compete competitively in order to represent their home country in the Olympics. Cash awards are also given at many of the major competitions for breaking records. Professional swimmers may also earn a living as entertainers, performing in water ballets.
Locomation by swimming over brief distances is frequent when alternatives are precluded. There have been cases of political refugees swimming in the Baltic Sea and of people jumping in the water and swimming ashore from vessels not intended to reach land where they planned to go. Swimming travel is central to the plot of the motion picture "Welcome". US president John F. Kennedy led his sailors swimming island to island after his torpedo boat was sunk in World War II, and his senator brother Ted Kennedy claimed to have left Chappaquiddick Island by swimming.
There are many risks associated with voluntary or involuntary human presence in water, which may result in death directly or through drowning asphyxiation. Swimming is both the goal of much voluntary presence, and the prime means of regaining land in accidental situations.
Most recorded water deaths fall into these categories:
- Panic where the inexperienced swimmer or non swimmer becomes mentally overwhelmed by the circumstances of their immersion, leading to sinking and drowning. Occasionally panic can kill through hyperventilation even in very shallow water.
- Exhaustion where the person is unable to sustain efforts to swim or tread water, often leading to death through drowning.
An adult with fully developed and extended lungs has generally positive or at least neutral buoyancy, and can float with modest effort when calm and in still water. A small child has negative buoyancy and will either sink rapidly or have to make a sustained effort to stay near the surface.
- Hypothermia where the person loses critical core temperature, leading to unconsciousness or heart failure.
- Dehydration from prolonged exposure to hypertonic salt water, less frequently salt water aspiration syndrome where inhaled salt water creates foam in the lungs that restricts breathing.
Hypothermia and dehydration also kill directly, without causing drowning, even when the person wears a life vest.
- Blunt trauma in fast moving flood or river water.
Less common are
- Other adverse effects:
- Exostosis is an abnormal bony overgrowth narrowing the ear canal due to frequent, long-term splashing or filling of cold water into the ear canal, also known as surfer's ear.
- Infection due to water-borne bacteria, viruses, or parasites.
- Chlorine inhalation (in swimming pools).
- Heart attacks while swimming (the primary cause of sudden death among triathlon participants, occurring at the rate of 1 to 2 per 100,000 participations.)
- Adverse encounters with aquatic life:
- Stings from sea lice, jellyfish, fish, seashells, and some species of coral.
- Puncture wounds caused by crabs, lobsters, sea urchins, zebra mussels, stingrays, flying fish, sea birds, and rubbish.
- Hemorrhaging bites from fish, marine mammals, and marine reptiles, occasionally resulting from predation.
- Venomous bites from sea snakes and certain species of octopus.
- Electrocution or mild shock from electric eels and electric rays.
Around any pool area, safety equipment is often considered important and is a zoning requirement for most residential pools in the United States. Supervision by personnel trained in rescue techniques is required at most competitive swimming meets and public pools.
In Sweden, Denmark, Norway, Estonia and Finland, the curriculum for the fifth grade (fourth grade in Estonia) states that all children should learn how to swim as well as how to handle emergencies near water. Most commonly, children are expected to be able to swim 200 metres (660 ft) – of which at least 50 metres (160 ft) on their back – after first falling into deep water and getting their head under water. Even though about 95 percent of Swedish school children know how to swim, drowning remains the third most common cause of death among children.
In both the Netherlands and Belgium swimming lessons under school time (schoolzwemmen, school swimming) are supported by the government. Most schools provide swimming lessons. There is a long tradition of swimming lessons in the Netherlands and Belgium, the Dutch translation for the breaststroke swimming style is even schoolslag (schoolstroke). The children learn a variant of the breaststroke, which is technically not entirely correct. In France, swimming is a compulsory part of the curriculum for primary schools. Children usually spend one semester per year learning swimming during CE1/CE2/CM1 (2nd, 3rd and 4th grade).
In many places, swimming lessons are provided by local swimming pools, both those run by the local authority and by private leisure companies. Many schools also include swimming lessons into their Physical Education curricula, provided either in the schools' own pool, or in the nearest public pool.
In the UK, the "Top-ups scheme" calls for school children who cannot swim by the age of 11 to receive intensive daily lessons. These children who have not reached Great Britain's National Curriculum standard of swimming 25 metres by the time they leave primary school will be given a half-hour lesson every day for two weeks during term-time.
In Canada and Mexico there has been a call for swimming to be included in the public school curriculum.
In USA there is the Infant Swimming Resource (ISR) initiative that provides lessons for infant children, to cope with emergency situation when they have fallen into water. They are taught how to roll-back-to-float (hold their breath underwater, to roll onto their back, to float unassisted, rest and breathe until help arrives).
Clothing and equipment
Standard everyday clothing is usually impractical for swimming and is unsafe under some circumstances. Most cultures today expect swimsuits to be worn for aquatic activities.
Men's swimsuits commonly resemble shorts, or briefs. Casual men's swimsuits (for example, boardshorts) are rarely skintight, unlike competitive swimwear, like jammers or diveskins. In most cases, boys and men swim with their upper body exposed, except in countries where custom or law prohibits it in a public setting, or for practical reasons such as sun protection.
Modern women's swimsuits are generally skintight, covering the pubic region and the breasts (See bikini). Women's swimwear may also cover the midriff as well. Women's swimwear is often a fashion statement, and whether it is modest or not is a subject of debate by many groups, religious and secular.
Competitive swimwear is built so that the wearer can swim faster and more efficiently. Modern competitive swimwear is skintight and lightweight. There are many kinds of competitive swimwear for each gender. It is used in aquatic competitions, such as water polo, swim racing, diving, and rowing.
Wetsuits provide both thermal insulation and floatation. Many swimmers lack buoyancy in the leg. The wetsuit reduces density, and therefore improves buoyancy while swimming. It provides insulation by absorbing some of the surrounding water, which then heats up when in direct contact with skin. The wetsuit is the usual choice for those who swim in cold water for long periods of time, as it reduces susceptibility to hypothermia.
Some people also choose to wear no clothing while swimming. This is known as skinny dipping. It was common for males to swim naked in a public setting up to the early 20th century. Today, skinny dipping can be a rebellious activity, or merely a casual one.
- Ear plugs can prevent water from getting in the ears.
- Noseclips can prevent water from getting in the nose. However, this is generally only used for synchronised swimming. Using noseclips in competitive swimming can cause a disadvantage to most swimmers. It is for this reason that noseclips are only used for synchronised swimming and recreational swimming.
- Goggles protect the eyes from chlorinated water, and can improve underwater visibility. Tinted goggles protect the eyes from sunlight that reflects from the bottom of the pool.
- Swim caps keep the body streamlined and protect the hair from chlorinated water.
- Kickboards are used to keep the upper body afloat while exercising the lower body.
- Pull buoys are used to keep the lower body afloat while exercising the upper body.
- Swimfins are used to elongate the kick and improve technique and speed. Fins also build upper calf muscles.
- Hand paddles are used to increase resistance during arm movements, with the goal of improving technique and power.
- Safety fencing and equipment is mandatory at public pools and a zoning requirement at most residential pools in the United States.
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- Drowning-Prevention.org, Drowning Prevention and Water Safety Information from Seattle Children's Hospital and the Washington State Drowning Prevention Network
- Physsportsmed.com, Swimming Injuries and Illnesses
- Swimmingstrokes.info, Overview of 150 historical and less known swimming-strokes