Swimmers and Swim Strength Training

By Mat Luebbers

Sport specific work is the best way to get better at that sport; if you want to be a better swimmer, then swim! But how can you make additional gains when you have maximized your swim time? One way is to add dryland swim work - flexibility exercises, plyometric work, swimming while wearing weights, and resistance training are some of the options. One example of resistance training is weight work aimed at adding strength and speed to your stroke.

What muscles are used in swimming? Almost all of them, from the top of your head through your toes. To maximize your time, this program will emphasis the major groups that should give your swimming some extra strength. This type of dryland work can help endurance, but other types of work, such as swim trainers (like the Vasa Trainer and the DrySwim Trainer and Exerciser) or stretch cords are better at this based on lower resistance and higher repetitions.

These are also a valuable part of any swimming program.

This is a basic plan designed to increase muscle strength. It can be more refined based on a particular need or a season plan. It may need to be modified based on what equipment you have available. You will use the routine two to three times each week, progressing through each phase. The first few sessions in each phase establish starting points for the rest of the sessions. The final phase is for the last four to five weeks before your biggest competition; you should stop lifting weights 10 days before the first day of the competition. To make gains, you are breaking down your muscles, then letting them rebuild. To give them the time to rebuild, do not lift two days in a row. To help prevent injury, do not "lift to failure"; always end feeling like you could do a few more.

Warm up before you begin any of the routines. Spend 10 to 20 minutes building your heart rate to increase blood flow, body temperature, and general range of motion; Place your general stretching routine after completing the weight routine, but you could do a short stretch for the muscle groups just used while you recover between exercises. Some warm-up ideas are stationary cycling, jogging, rowing, or jumping rope.

Keeping a log book is vital. Record the date, time, phase, lifts (including sets and repetitions), amount of weight for each lift, and other comments for the day, like general feeling about the workout. You will use this information throughout the program to track your progress.

An additional area to be aware of is muscle balance (thanks for the reminder, Mikey 810). Swimmers can do some simple shoulder exercises to maintain strength balance in the rotator cuff/shoulder girdle area every day with stretch cords or barbells if desired; this can help prevent shoulder injury.

The exercises used in this program are: Squats, Leg Press, Leg Extension, Leg Curl, Lat Pull-down, Seated Rowing, Bent-over Rowing, Lateral Raise, Shoulder Press, Bench Press, Dumbbell Curl, Push-up, Abdominal Work and Assorted Stretches.

This workout program uses three different phases. The first phase is to either get you started or to build strength. The second phase is to take your strength gains and build on them. The third phase is for the last three to four weeks before your biggest competition, and you should stop the routine 7 - 14 days before the first day of the competition. You are going to maintain most of your strength gains, build more muscular power, and begin to reduce the stress to your muscles so they are fully recovered by your big event.

Remember to start light and gradually increase the weights; slow progress is the key to good strength gains without injury! Keep that log book, hit the weights, and feel yourself get stronger in the pool.

Swim On!

Source : About.com

Who Needs Water: Improving Swimming Through Dry-Land Fitness

by Dan Frost

I started exploring the subject of dry-land exercises for swimmers a few months ago, mostly driven by pure necessity. You see, I am a U.S. Navy flight officer spending six months aboard an aircraft carrier about 6000 miles from home, and far enough away from any swimming pool. My goal is to come back from my deployment able to swim as well as I did before leaving. My problem is trying to do that without much opportunity to actually swim.

The value of other exercises and physical activities in improving swimming performance seemed to me to be a source of great debate. I have heard people say things like "The only way to being a better swimmer is to swim (faster)," but I know that all of the college swim teams do various exercises away from the pool. Nonetheless, many experts agree that there are certain dry-land exercises which can improve your swimming.

Terry Laughlin, famous for his Total Immersion swim camps, has what he calls his "Rule of 70." His principle being that 70 percent of swimming performance comes from swimming technique and skill; the ability to efficiently propel through water. The remainder (I assume) is fitness. It is important to recognize that there are two distinct facets of swimming performance: Fitness and skill.

I think of the skills of swimming as perishable, in that they tend to fade away without practice. In many ways, it is like learning to ride a bicycle or landing a plane on an aircraft carrier. Once you learn how to do it, you do not forget, but you do not perform either task well if you have not practiced for a while. We can only practice swimming skills in the water. However, remember that skill is only a part of swimming well. Improving swimming fitness can be done both in and out of the water.

According to coach Ernest Maglischo in his book Swimming Even Faster (pg. 69-71), he states that "The major adaptations [in swim training] ... take place in the muscular system. Adaptations in the respiratory and circulatory systems, while probably contributing to improvements in performance, are not as important as those that are produced in the muscles." Here he explains that there are Central training effects which improve the cardiovascular system through various forms of exercise, and Peripheral training effects improving only the specific muscle fibers exercised.

Exercises away from the pool can help our swimming, particularly if they provide the peripheral training effects. That is, they must work, or specifically train, the same muscles used in swimming. Other exercises that do not provide peripheral training effects (e.g. running) provide central effects that help to improve general conditioning. College swimming teams routinely advocate general conditioning workouts in the pre-season and early season in order to get the body in shape before the long swimming workouts begin in earnest.

There are four different types of dry-land activities that can help your swimming: Stretching, Abdominal Exercises, Weight Training, and General Exercises.

Stretching is an activity that can be done practically anytime. Your ability to convert your mechanical energy into propulsion in the water depends in part on your flexibility, and thus your ability to move water faster and in the proper direction. Proper stretching also helps to keep your muscles warm and limber, reducing the chances for injury. Many books on swimming have chapters on proper stretching techniques (it can be dangerous if overdone). This is one task that I have found easy to do while on the carrier.

I particularly note Abdominal Exercises apart from resistance/weight training in general for two reasons. One reason is that the "abs" are a key aspect of swimming, being the source of power for proper body rotation, propulsion through the legs, and turning. The other is that no special apparatus or machine is required to do these exercises. I recommend performing exercises that are "spine-safe" in that they do not place undue stress on the spine and lower back. Instead of full sit-ups, use crunching movements instead. A company called Health for Life publishes a small manual called Legendary Abs II that I recommend because I have seen college programs like Stanford University pick up on the same exercises. I too have no problem doing these exercises aboard ship.

Many advocates of Weight Training advocate "circuit training" among various exercise stations. They also recommend specifically targeting the muscles like shoulders, back and arms for the peripheral training effects. Jane Moore, in her April president's letter to the WetSet, also advocated resistance training to combat the effects of aging. Again, many swimming books have sections on weight training, although not all agree on the specific exercises that should be employed. Maglischo, for example (p. 644), recommends against push-ups, military presses and dips because of the strain these exercises exert within the shoulder. If you can find a good fitness club or gym with a weight training room, there is usually a certified trainer there who can advise you on starting a beneficial program. Also, it is a good idea to lift after swimming if you choose to do both on the same day. I am fortunate enough to have two small weight rooms aboard my carrier, but rarely use them because I must share the facilities with 5000 other sailors. When I do get into the gyms, I use the machines for triceps presses, lat pulldowns, chest presses and leg curls.

There are a number of other exercises that I do aboard ship which should help my swimming to some degree. I have a pair of stretch cords that I use for resistance training either with swimming stroke movements or with pressing/pulling movements. Jogging on the flight deck or riding stationary bikes help with cardiovascular fitness and leg strength. Other fitness exercises often mentioned for improving swimming include the use of dry swim trainers or swim benches and medicine balls. Also mentioned are plyometric exercises utilizing powerful jumping movements.

Hopefully, these ideas will help you become a better swimmer as well as a more rounded athlete. Personally, I can't wait to get home and find out for myself if they work (My coach already wrote me to say that she'll be having 3000 meter workouts with 3x400IM descending at 5:00 A.M. when I return).

About the Author

Dan Frost is past vice-president of the Masters Aquatics Coaching Association. Taken from Masters Aquatic Coaches Association, and reprinted from the Wet Set, July 1996)

Source : Alexandria Masters Swimming

Swimming Machine

A swimming machine is a resistance swimming apparatus, often self-contained, enabling the swimmer to swim in place. This may be accomplished either by accelerating the water past the swimmer or by supporting the swimmer, either in water or on dry land. The first type, known as a countercurrent swimming machine, usually consists of a water tank at least twice as long and about one and a half times as wide as an average person with the limbs extended. The swimmer swims unrestrained against an adjustable stream of water set in motion by means of mechanical devices, such as jets, propellers or paddle wheels.

Countercurrent swimming machines made their appearance in the 1970s, initially in the form of pump-driven jetted streams, which caused a certain amount of turbulence and an un-natural swimming environment. They were followed up in the 1980s by propeller- and paddle-wheel driven machines. These provided a smoother stream of water. Many users find them relatively easy to swim in, though some are bothered by the considerable chop – inherent to these small pools, especially when performing symmetrical strokes such as the breaststroke or the butterfly. These machines are also criticized for being expensive, noisy, and wasteful of energy. (A typical machine requires special power connections delivering 3 to 4 kW for the pressure-driven machines, and 6.5 to 11 kW for the volume-driven machines, aside from any power needed to heat and filter the water--usually an additional 5 kW for an electric heater and around 1.5 kW for a pool pump and filter.)

Two types of exercise machines make up the second group. Hybrid systems - self-contained micropools similar to the counter-current type but using a flexible tether to keep the swimmer in place are one type. These systems, being human powered, need neither machinery or electricity but have to be carefully designed to suppress wave formation. The second type of swimming machine allows a person to remain on dry land while simulating certain swimming strokes. Machines of the latter type however can not compensate for the weight of the body and the limbs and thus deprive the user of the benefits of exercise in an aquatic environment. However, the higher effort required by such machines, in the absence of the metabolic effects of immersing the body in water, makes these devices more effective than true swimming if one's purpose is to achieve weight reduction. Similar in purpose, but not qualifying as swimming machines since they require access to a swimming pool, are various tether systems.

Pressure-Driven Machines

These systems depend on one or more pumps. The best ones are engineered to maximize the volume of water delivered, at the expense of high head which here is not needed as the water need not be lifted, only set in motion. Discharge rates of 13 L/s (200 US gal/min) and more are possible, from motors of three or four horsepower (2 or 3 kW). One of the earliest models on the market - introduced in 1973 - was the Badujet which is available only in the form of a bare propulsion system, to be installed into either an existing or newly-built pool.

Also in this category are a number of swim spas, usually fiberglass shells equipped with several pool pumps to set the water in motion. Seen as more convenient since they come pre-assembled, the quality of the swim has been criticized as being somewhat turbulent, as the strength of the current comes from the speed and pressure of the discharged water, rather than its volume.

Volume-Driven Machines

In the 1980s a new type of machine made its appearance. In an attempt to correct problems of turbulence and resulting discomfort from swimming against a jet of water, systems were devised to set the water in motion in a smoother fashion. The first, in 1984, was the SwimEx, developed by Stan Charren together with two MIT-trained engineers. This machine, consisting of a fiberglass pool with the machinery housed in an adjacent compartment, sets the water in motion by means of a paddle-wheel, thus generating a steady stream of water as wide as the swimming pool itself.

In the late 1980s the Endless Pool® was developed by James Murdock, in an attempt to build a less-expensive alternative to the SwimEx. This machine places the water-moving equipment - a large propeller encased in a stainless steel box and powered by a remote hydraulic pump, and its stainless steel water circulation tunnels - inside the body of a vinyl-lined metal pool. Its stream of water is narrower than that of the SwimEx, though the swimming experience is comparable. A couple of copy-cat systems have sprung up since its introduction.

Around the same time, the Swim Gym, a propeller-driven propulsion system developed by engineer Peter Davidson became available commercially. This machine is encased within a large (10" diameter) PVC tee which is then incorporated into the concrete wall of a swimming pool. It delivers a current equivalent to that produced by the Endless Pool.

Hybrid Systems

A number of "still-water" mini-pools have been built over the years, designed to be used in conjunction with various resistance-swimming tether systems. These human-powered devices combine the self-contained aspect of counter-current swimming machines with the low cost and simplicity and freedom of movement of tether systems used in athletic training. They have major cost and energy-use advantages over mechanical swimming machines. They are valuable for aerobic exercise, endurance and strength training, and for stroke practice. However, they cannot replicate open water conditions, in which the water courses at speed past the swimmer, so that for competition training their use has to be combined with open-water practice. One example of such a device is the Swimergy Swim System, which also makes use of wave-reduction technology.

Dry-Land Swim Training Machines or Swim Benches

Since the 1800s, a number of dry-land swimming simulators have been designed to hold a person in a position in which swimming motions could be carried out. The earlier swim training devices were devised for swimming instruction, while later machines were built for the purpose of physical exercise. The Vasa Trainer, Vasa Ergometer and DrySwim Trainer and Exerciser are examples of the latter type. These machines of course are completely silent and require no electricity.

The Vasa Trainer, introduced in 1988, is a sport-specific, strength training machine. You can do over 200 exercises for strength, endurance, power, and rehabilitation, making the Vasa Trainer one of the most versatile exercise machines available today. It works by lifting your body weight up the inclined monorail and then lowering it back down. It has many slope incline settings as well as several other options for changing resistance. It allows swimmers (and surfers, triathletes, physical therapists) to simulate swim strokes to improve technique while increasing functional strength.

The Vasa Ergometer was introduced in 2004. The "erg" allows athletes to simulate swim strokes with variable wind resistance that can be adjusted to feel like a fast or slow current. You can vary the resistance, your stroke rate and your stroke power to fine tune each workout - from light, range of motion, rehab work to swim-set simulations to race intensity simulations to maximum power intervals. An electronic performance monitor that provides precise feedback for: time; distance; pace; stroke rate; right & left arm force; and watts. If one side is weaker than the other, the monitor displays it. It is ideal for doing repeatable training workouts, performance testing, or even indoor racing without getting wet. This latter point is important and useful for those people who have allergies, skin problems or respiratory ailments caused by swimming in harsh pool environments.

The DrySwim Trainer and Exerciser, invented by Swim Coach James Davis and Chief Engineer Paul Dowd, is the first truly ergonomicly designed exercise machine for swimmers. The DrySwim Trainer conforms to the natural and desired body rotation to maintain a steady pace while conserving energy and swimming with “the body” and not just the “arms and legs”. There is nothing that you can do in the water that you can't do on the DrySwimTrainer. You can train distance or sprints. You can do long workouts or short ones. You can do drills including "the catch up" or "single arm drills". In fact, swimming on The DrySwim Trainer burns more fat then swimming the same workout in the water.

Source : Wikipedia

Dry Swim Trainer : The Next Best Thing to Water

The history of Swim Machines and Dry Swim Trainers is a rich one. Since the 1800s, a number of dry swim trainers or simulators have been designed to hold a person in a position in which swimming motions could be carried out. The earlier devices were devised for swimming instruction, while later machines were built for the purpose of physical exercise. Swim machine inventors had many early dry swim trainer models before inventing ones that really work. And so, efficient freestyle swim training can now be accomplished in a totally dry home or health club setting.

Today, a quick glance at most swimming magazines will reveal ads for these dry swim trainers. Their use to clubs and competitive swimmers is very much a topic of current debate in sports science. Although swimming strokes each involve a unique, integrated pattern of neuro-muscular and joint actions, the body position and movements involved in dry swim trainer exercise suggest that this type of training may effectively imitate actual swimming. The potential advantage over true swimming, of course, is the possibility of increasing resistance to movement in excess of that usually encountered. Thus the overload principle of training can be allowed to take effect - the artificially increased training stimulus should hopefully result in greater power gains. Another use may be in observing an individual swimmer's stroke pattern so that immediate instruction and feedback can be given. Those who can afford to purchase a dry swim trainer can also have a computer-interfaced system for analysis of power output and movement pattern on-screen.

A recent study, from the same laboratory in Japan that carried out the work on hand paddles, has compared the peak oxygen uptake between dry swim trainer exercise and arm-stroke-only swimming. The authors had correctly identified a gap in the research where no one had yet determined whether the two forms of exercise actually required similar amounts of oxygen under maximal conditions.

The researchers found that the use of these ergonomic exercise machine for swimmers, when performed at the maximum intensity possible, required over 20 per cent less oxygen than arm-stroke-only swimming. A possible reason for this appears when one considers that oxygen requirements are very highly related to the size of the muscle mass involved in the exercise - in other words, does dry swim trainer exercise use less muscle? Most dry swim trainers require the user to work against a resistance while pulling the arm to the rear position, but during the recovery little or no resistance is felt, or the arm may even be drawn forward. However, during actual swimming, voluntary recovery must take place with some considerable physical effort, which ultimately has an oxygen cost associated with it.

An additional reason may be that the torso is completely supported on most dry swim trainers. The dry swim trainer conforms to the natural and desired body rotation to maintain a steady pace while conserving energy and swimming with “the body” and not just the “arms and legs”,
whereas during swimming the postural muscles of the upper body must be recruited to both maintain optimum horizontal positioning and initiate rotation around the head-feet axis.

In summary, this very recent research suggests that the cardiovascular stress induced during dry swim trainer exercise is not comparable to that met in arm-stroke-only swimming. Thus, if the perceived advantage of dry swim trainer exercise exists, it should certainly be combined with significant amounts of traditional training to ensure a proper training stimulus (Ogita and Taniguchi, 'The comparison of peak oxygen uptake between swim-bench exercise and arm stroke', European Journal of Applied Physiology, 1995, vol.71, pp 295-300).

Source : Peak Performance

Where Swimming Started

Drawings from the Stone Age were found in "the cave of swimmers" near Sura in the southwestern part of Egypt. Written references date back up to 2000 B.C. In 1538 Nicolas Wynman, German professor of languages, wrote the first swimming book. 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 1896 Summer Olympics games in Athens. In 1900 backstroke was included as an Olympic Event. In 1902 the trudgen was improved by Richard Cavill, using the flutter kick. In 1908, the world swimming association Federation Internationale de Natation was formed. Butterfly was first a variant of Breaststroke, until it was accepted as a separate style in 1952.

Technique

The human body is composed primarily of water, and it has a very similar density to water. Roughly, 70% of the body is water; while the lungs are filled with the air, the body 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. This propelling is accomplished by using the hands and forearms as paddles, and by kicking the legs to push water away from the body (though kicking accounts for relatively little overall). Since salt water (e.g., the ocean) is denser than fresh water (e.g., most swimming pools), less effort is required to stay afloat in salt water than in fresh water.

A number of swimming styles have been developed based on the implementation of some or all of the following principles: The torso and the legs should be kept as parallel as possible 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.

Recent research has shown that hand force applied to the water is really generated by the rotation of the hips, and not by the muscles of the arm. The muscles that pull the arm through the water are attached within one inch of the top of the arm. With a 21" arm, the lever ratio is 1:20, which means that a 100 lbs. of pull by the shoulder muscles produces only 5 lbs. of force at the hand as it pushes back against the water. The torque generated by the larger, stronger hip muscles, on the other hand, whips the hands through the water, much like golfers or batters whip their clubs and bats through the air with a fast turn of the hips. Elite swimmers who were able to make modest increases in the acceleration of their hips doubled their peak hand force output.

The time spent on the side should be maximized so the shoulders do not break the water-line and do not produce bow waves. 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 the back to the front should be in the air for as much time during the recovery stroke as possible, and in the water, oriented as hydrodynamically 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 (which increases with the cube of the speed) of an equal amount of torso frontal area. Rotating your shoulders also adds power to one's pull by using abdominal muscles to help pull the arm through the water.

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.

Another technique that can help an athlete swim at a higher performance level is proper breathing techniques. Breathing correctly can make you swim faster and make it harder for you to be fatigued. Competitive swimmers take in one breath and gradually let it out over three to four strokes. As the race progresses and the swimmer becomes tired, less oxygen from those breaths reach his muscles. You can practice and teach your body how to run on less than normal levels of oxygen. Take a deep breath at one side of a pool, submerge yourself fully, and kick like a dolphin. Try to simulate a torpedo. Try crossing the pool with one breath, and once you can do that extend the distance. Another way you can practice endurance is by taking a breath and letting it out over six strokes (while freestyle swimming).

Skeletal animation and computational fluid dynamics allow simulation of swimmers. This allows to quantify forces on joints and muscles, and, if multiple simulations are employed, to compare different styles or individuals. By means of computer graphics or motion capture the simulation can be compared to real swimmers. While this removes many doubts, it is still guess work needed to create new styles, it is a didactic challenge to formulate a manual for swimmers, and the feel of the water is still needed to close a control loop so that the swimming styles does not drift away afterwards

Competitive swimming

The goal of competitive swimming is to be the fastest to swim a given distance. Competitive swimming became popular in the nineteenth century, and currently comprises 34 events - 17 male events and 17 female events. Swimming is a popular event at the Summer Olympic Games, where male and female athletes compete in 13 of the recognized events each. Olympic events are held in a 50 meter pool. Competitive swimming's international governing body is FINA (Fédération Internationale de Natation), the International Swimming Federation.

The four competitive strokes are the butterfly, backstroke, breaststroke, and freestyle (frontcrawl). Also, there are different times to get to different levels in these strokes. These strokes can be swum individually or together in an individual medley.

Recreational swimming

The most common purpose for swimming is recreation. Recreational swimming is considered by many a good way to relax, while enjoying a good full-body workout. Several swimming styles are suitable for recreational swimming; most recreational swimmers prefer a style that keeps their head out of the water and has an underwater arm recovery. Breaststroke, side stroke, and 'dog paddle', are the most common strokes utilized in recreational swimming, but the out-of-water arm recovery of freestyle or butterfly gives rise to better exploitation of the difference in resistance between air and water.

The butterfly stroke, which consists of out-of-water recovery with even symmetry in body movements, is most suited to rough water swimming. For example, in a record-setting example of endurance swimming, Vicki Keith crossed the rough waters of Lake Ontario using butterfly. Most recreational swimming takes place in pools, where the water is calm. Therefore freestyle (which does not work as well in rough water) is suitable.

Occupational swimming

Some occupations require the workers to swim. 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 by lifeguards or members of the Coast Guard. The training of these techniques has also evolved into competitions such as surf lifesaving.

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. 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, such as 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.

Swimming has become a professional sport as well. Companies such as Speedo and Tyr Sports, Inc. sponsor swimmers just as Nike sponsors basketball players (Nike also sponsors swimmers). Cash awards are also given at many of the major competitions for breaking records.

Ocean swimming

Ocean swimming is the sport of swimming and racing in the sea. Ocean swimming is popular in Australia, America and the Pacific Islands. Famous swims include the Alcatraz challenge which is a swim from Alcatraz island to the mainland.

Swimming for exercise

Swimming is an excellent 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. Therefore, swimming is frequently used as an exercise in rehabilitation after injuries or for those with disabilities.

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 swimming in a confined space for athletic or therapeutic reasons. Resistance swimming can be done either against a stream of moving water (often termed a swimming machine) or by holding the swimmer stationary with elastic attachments.

Swimming is primarily an 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 it is believed to reduce the harmful effects of stress.

Source : Wikipedia

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