Why You Float At All
Swimming works because of a very narrow margin. On average the human body has a relative density of 0.98 compared with water, which means it is just slightly lighter, and so it floats.
That margin is thin enough to be changed by all sorts of things: body composition, how inflated your lungs are, how much muscle and fat you carry, where your centre of gravity sits, and how salty the water is. More body fat and saltier water both lower your relative density and make you more buoyant.
This produces a difference that has nothing to do with skill. Because they tend to have a lower centre of gravity and higher muscle content, human males find it harder to float.
The same near-neutral buoyancy is why swimming is described as low-impact compared with land activities such as running. The water is carrying your weight, so your joints are not.
Fighting the Water You Are Pushing Against
Water is dense and viscous, and that creates resistance to anything moving through it. Swimming strokes use that resistance to generate propulsion, which means the same property that pushes you forward also holds you back as drag.
Every swimmer is managing both sides of that trade at once.
There are two ways to go faster: increase the power of your strokes, or reduce the resistance you are fighting. The arithmetic strongly favours the second. Power has to increase by a factor of three to achieve the same effect as reducing resistance.
That is why technique beats effort in the water to a degree it rarely does on land. Swimming efficiently means holding a horizontal position, rolling the body to reduce how wide you are as you move through the water, and extending the arms as far as possible. Hydrodynamics, in other words, is not a refinement on top of swimming. It is most of the sport.
Four Strokes, One of Them Fastest
Swimming is the self-propulsion of a person through water, achieved by coordinating limb and body movements to produce buoyancy and forward thrust.
It is a whole body exercise, requiring endurance, skill and efficient technique to get the most speed for the least energy. The repeated motions that move you forward are called strokes.
There are four main ones, and they are not equal. The front crawl, also known as freestyle, is widely regarded as the fastest. The others are practised for particular purposes, including training and competition, rather than because they are quicker.
As a formal sport, swimming appears in local, national and international competition, and it has featured in every modern Summer Olympics without exception. It is also consistently among the most popular public recreational activities anywhere, and in some countries swimming lessons are a compulsory part of the school curriculum, which is true of very few other sports.
The Sport With a Death Rate
Swimming carries risks that most sports do not, and they come from the environment rather than the activity.
A swimmer can be incapacitated by panic and by exhaustion, and both are potential causes of death by drowning. Other dangers come from exposure to infection, or from hostile aquatic wildlife. This is the reason most facilities employ a lifeguard specifically to watch for signs of distress, a role with no real equivalent in most other sports.
Set against that, the health case is unusually strong. Swimming strengthens cardiovascular health, builds muscle strength and increases flexibility, and because the water carries your weight it suits people of all ages and fitness levels.
The equipment list is short and optional: goggles, flotation devices, swim fins, paddles and snorkels can each enhance the experience or the performance, but none of them are required. Swimwear itself varies by local culture, with some swimmers wearing everyday clothes or nothing at all.
