Science

Swimming relies on the nearly neutral 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 based on body composition, lung inflation, muscle and fat content, centre of gravity 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 buoyancy. Because they tend to have a lower centre of gravity and higher muscle content, human males find it more difficult to float or be buoyant. See also: Hydrostatic weighing.

Since the human body is less dense than water, water can support the body’s weight 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.

Hydrodynamics is important to stroke technique for swimming faster, and swimmers who want to swim faster or exhaust less try to reduce the drag of the body’s motion through the water. To be more hydrodynamically effective, swimmers can either increase the power of their strokes or reduce water resistance. However, power must increase by a factor of three to achieve the same effect as reducing resistance.^[7] Efficient swimming by reducing water resistance involves a horizontal water position, rolling the body to reduce the breadth of the body in the water, and extending the arms as far as possible to reduce wave resistance.^[7]

Just before plunging into the pool, swimmers may perform exercises such as squatting. Squatting helps enhance a swimmer’s start by warming up the thigh muscles.^{[8][clarification needed]}

Infant swimming

Main article: Infant swimming

Human babies demonstrate an innate swimming or diving reflex from newborn until approximately ten months.^[9] Other mammals also demonstrate this phenomenon (see mammalian diving reflex). The diving response involves apnea, reflex bradycardia, and peripheral vasoconstriction; in other words, babies immersed in water spontaneously hold their breath, slow their heart rate, and reduce blood circulation to the extremities (fingers and toes).^[9] Because infants exhibit instinctual swimming behaviors, classes for babies about six months old are offered in many locations, and formal training is recommended to reinforce these abilities.^[10] This helps build muscle memory and makes strong swimmers from a young age.

Technique

See also: Swimming stroke

Swimming can be undertaken using a wide range of styles, known as ‘strokes,’ and which are used for different purposes or to distinguish between classes in competitive swimming. Using a defined stroke for propulsion through the water is unnecessary, and untrained swimmers may use a ‘doggy paddle‘ of arm and leg movements, similar to how four-legged animals swim.

Four main strokes are used in competition and recreational swimming: the front crawl, breaststroke, backstroke, and butterfly.

In non-competitive swimming, there are some additional swimming strokes, including the sidestroke. The sidestroke, toward the end of the 19th century, changed this pattern by raising one arm above the water first, then the other, and then each in turn. It is still used in lifesaving and recreational swimming.

Other strokes exist for particular reasons, such as training, school lessons, and rescue, and it is often possible to change strokes to avoid using parts of the body, either to separate specific body parts, such as swimming with only arms or legs to exercise them harder, or for amputees or those affected by paralysis.

History

Main article: History of swimming

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 BCE. Some 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 450 BC, Herodotus described a failed seaborne expedition of Mardonius with the words “…those who could not swim perished from that cause, others from the cold”.^[11]

The coastal tribes living in the volatile^{[clarification needed]} Low Countries were known as excellent swimmers by the Romans. Men and horses of the Batavi tribe could cross the Rhine without losing formation, according to Tacitus. Dio Cassius describes one surprise tactic employed by Aulus Plautius against the Celts at the Battle of the Medway:^[12]

The [British Celts] thought that Romans would not be able to cross it without a bridge, and consequently bivouacked in rather careless fashion on the opposite bank; but he sent across a detachment of [Batavii], who were accustomed to swim easily in full armour across the most turbulent streams. … Thence the Britons retired to the river Thames at a point near where it empties into the ocean and at flood-tide forms a lake. This they easily crossed because they knew where the firm ground and the easy passages in this region were to be found, but the Romans in attempting to follow them were not so successful. However, the [Batavii] swam across again and some others got over by a bridge a little way up-stream, after which they assailed the barbarians from several sides at once and cut down many of them.

The Talmud, a compendium of Jewish law written compiled c. 500 CE, requires fathers to teach their son how to swim.^[13]

In 1538, Nikolaus Wynmann, a Swiss–German professor of languages, wrote the earliest known complete book about swimming, Colymbetes, sive de arte natandi dialogus et festivus et iucundus lectu (The Swimmer, or A Dialogue on the Art of Swimming and Joyful and Pleasant to Read).^[14][11]

Competitive swimming in Europe started around 1800, mostly using the breaststroke, which started as the current breaststroke arms and the legs of the butterfly stroke. In 1873, John Arthur Trudgen introduced the trudgen to Western swimming competitions.^[15] Swimming was introduced as a competitional sporting event in the 1896 Summer Olympics in Athens, Greece.

The butterfly was developed in the 1930s and was considered a variant of the breaststroke until it was accepted as a separate style in 1953.^[16]

Purpose

There are many reasons why people swim, from 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 and muscle injuries. Professional opportunities in swimming range from competitive sports to coaching, lifeguarding, and working in aquatic therapy. Some may be gifted and choose to compete professionally and go on to claim fame.

Recreation

Many swimmers swim for recreation, with swimming consistently ranking as one of the physical activities people are most likely to participate in. Recreational swimming can also be used for exercise, relaxation, or rehabilitation.^[17] The support of the water and the reduction in impact make swimming accessible for people unable to undertake activities such as running. Swimming is one of the most relaxing activities, and water is known to calm us and help reduce stress.

Health

Swimming is primarily a cardiovascular/aerobic exercise^[18] due to the long exercise time, requiring a constant oxygen supply, except for short sprints where the muscles work anaerobically. Furthermore, swimming can help tone and strengthen muscles.^[19] Regular swimming can help in weight management and contribute to maintaining a healthy body weight. (Robinson 2022) Swimming allows sufferers of arthritis to exercise affected joints without worsening their symptoms. Swimming is often recommended for individuals with joint conditions or injuries, as the buoyancy of water reduces stress on the joints. Under the right conditions, it is also an excellent form of exercise for children and senior citizens. However, swimmers with arthritis may wish to avoid swimming breaststroke, as improper technique can exacerbate arthritic knee pain.^[20] As with most aerobic exercise, swimming reduces the harmful effects of stress. Swimming also improves health for people with cardiovascular problems and chronic illnesses. It is proven to impact the mental health of pregnant women and mothers positively. Swimming can even improve mood.^[21] Although many forms of physical activity have been shown to improve bone density and health, this is where swimming has its downfalls. Due to the low-impact nature of the sport, studies have demonstrated that bone mass acquisition will be negatively impacted, which could be an issue for adolescent athletes in particular.^[22] A 2025 study found that swimming outdoors is associated with greater levels of well-being. However, ‘wild swimming’ or open water swimming, where swimming takes place in rivers, lakes or the sea, has been found to be associated with higher well-being than swimming in outdoor pools.^[23]

Disabled swimmers

Since 2010, the Americans with Disabilities Act has required that swimming pools in the United States be accessible to disabled swimmers.^[24]

Elderly swimmers

“Water-based exercise can benefit older adults by improving quality of life and decreasing disability. It also improves or maintains the bone health of post-menopausal women.”^[25] Swimming is an ideal workout for the elderly, as it is a low-impact sport with very little risk of injury. Exercise in the water works out all muscle groups, helping with conditions such as muscular dystrophy which is common in seniors. It is also a common way to relieve pain from arthritis.

Sport

Main article: Swimming (sport)

Swimming as a sport predominantly involves participants competing to be the fastest over a given distance in a certain period of time. Competitors swim different distances in different levels of competition. For example, swimming has been an Olympic sport since 1896, and the current program includes events from 50 m to 1500 m in length, across all four main strokes and medley. During the season competitive swimmers typically train multiple times per day and week to increase endurance, strength, and preserve fitness. Furthermore when the cycle of work is completed swimmers go through a stage called taper where intensity is reduced in preparation for competition season. During taper, focus is on power and water feel.

The sport is governed internationally by World Aquatics, formerly known as FINA (Fédération Internationale de Natation) before it adopted its current name in December 2022. World Aquatics recognizes competitions of the 25 meter and 50 meter pools for International Competitions. In the United States, a pool of 25 yards in length is commonly used for competition, especially in the College Level.

Other swimming and water-related sporting disciplines include open water swimming, diving, synchronized swimming, water polo, triathlon, and the modern pentathlon.