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The main aim of this article is to provide an introduction into physiological effects and variations that could be useful for specific aquatic programming.

The Effect of Water

Water is approximately 800 to 1000 times more dense than air. This increased density has several effects on the body.

Effects on energy costs - Water density places an increased "drag" across the body through wave drag, skin friction drag and pressure drag. This means that the energy yield required for swimming is greater than that of dry-land activities (over the same duration and distance). McArdle, Katch & Katch state that "the energy cost of swimming a given distance is about four times greater than running the same distance."

Effects on the cardio respiratory system - The increased density of water also affects the cardio respiratory system of the body and reduces vital capacity by around 10 percent. This decrease is thought to be caused by the increased impendence placed on respiratory muscles and higher blood redirection to the thorax. Homer and associates have also found that VO2 values - as well as heart rates - are lower (by approximately 15 percent) when swimming as compared to running. Explanations for this effect include:

Another focal point is the difference between non submerged activities, which enables "free" breathing and those, like swimming, that require a breathing cycle and in effect cause a "forced" inspiration rate.

In swimming, inspiration rate is required to comply with arm patterns, hence breathing is forced.

How this forced respiration affects the average athlete is still under examination. However, the hypoxic effects need to be remembered, especially when prescribing certain drills. (This will be discussed further on.)

Effects on thermoregulation - Cool water also affects the thermoregulation of the body and increases susceptibility to hypothermia. A study conducted by Pugh and Edholm of two ultra distance swimmers in 150 degree Celsius water showed the following results: "The larger and fatter individual showed no decrease in rectal temperature for seven hours... The lighter, leaner individual was taken from the water after half an hour when his rectal temperature had dropped from 370 to 34.50 degrees Celsius."

Effects on weight bearing - Due to the previously discussed hydrostatic pressure, immersion in water supports the weight of the body. When immerged up to the neck, the body is only required to support only eight percent of its weight. When immerged up to the xiphoid process, a male is required to support 35 percent of his body weight while a female is required to support only 28 percent. When determined from the hips (ASIS), the male supports 54 percent while the female supports 47 percent of their body weights, respectively. These weight-bearing properties explain why water is such a valuable recovery and rehabilitation aid.

Training Methods

According to Rielly et al, "the physiological principals governing the general training programs of swimmers are similar to those under lying cycling or middle distance training."

Although the underlying training principals may be the same, it should be remembered that, due to the nature of water and the fact that swimming activates a relatively smaller muscle mass than running (legs contribute to only 10 to 15 percent of forward momentum in swimming), maximal heart rates are 10 to 13 beats per minute lower in both the trained and untrained athlete. As such, they recommend that for swimming activities, the predicted maximal heart rate be lowered by approximately 13 beats per minute (prior to determining training heart rates).

In regards to the content of a technical swimming session, advice by Boomer, a swim coach at the University of Rochester New York, should be considered. He proposes that 70 percent of successful swimming comes from reduced drag and only 30 percent from hand movement. This means that the emphasis of hand technique may not be as important as that placed on streamlining and reduction of drag.

Triathletes, due to high amounts of running and cycling, usually have poor planterflexion, thereby decreasing the streamlined position of the body, according to Town & Kearney.

Training Variations

Dry-land Training - Dry-land training not only involves technique work but also resistance training. At current, the most applicable form of specific dry-land resistance training utilizes boards and pulleys to mimic the swimmers actions as closely as possible. However, as Rielly et al. state, "Dry-land training may offer some benefit, but there is no guarantee of inevitable transfer to the aquatic environment."

Speed Resisted Work - As the name implies, speed resisted work involves applying resistance to the swimmer's speed. This form of overload helps to improve muscular power but may affect technique. Examples of speed resisted methods include the following:

Speed Assisted Work - Speed assisted work enables a swimmer to exceed current race speed and has shown improvements in young swimmers. Examples of speed assisted work include the following:

wpe22.jpg (10350 bytes) Figure 1 - Variety of swimming equipment used to enhance performance.


In several instances, like initial start and turns, swimmers hold their breath for extended submerged periods. This forced breath holding manoeuvre causes an increase in CO2 and may lead to hypoxia, hypercapnia or a combination of both, commonly referred to as hyperventilation. Hypoxia is a lack of oxygen that may lead to fainting. Hypercapnia is a condition caused by an increase in CO2, which stimulates breathing. It is a combination of these two elements that commonly leads to drowning. As swimmers require a forced inspiration, oxygen flow is purposely impeded, and instructors should be wary of prescribing activities, like high repetition turn training, which involves a forced breath holding manoeuvre. This may, in extreme circumstances, lead to hypoxia and then hypercapnia.

Swim Clothing

Caps - Caps not only reduce drag but also help keep the hair dry (for those aesthetically minded). However, the hair may still be a little damp after a training session due to the trapped sweat. After use, the cap should be washed with clean water and hand dried. Talcum powder should be placed in the centre to prevent the edges from sticking together.

Goggles - With goggles, it is important to check the fit and ensure that the nosepiece does not dig into the skin. Straps that divide into two pieces at the rear hold their place better than those with just a single continuous strap; however, they also increase drag, although only slightly.

Bathers - After swimming, bathers should be washed out with fresh water (shower with them) and visually inspected for damage. Depending on the cut of the bathers, some chaffing may be experienced. For ladies, collars rubbing against the neck or a necklace can cause chaffing across the neck. If the bathers do chaff, the affected skin should be covered with Vaseline to help reduce the friction.

T-shirts - Many pools do not allow people to swim with T-shirts on. When wet, the weight of the T-shirt hinders swimming. From a safety point of view, it makes self rescue and assisted rescues more difficult. Lycra swim tops are available and can provide sun protection without the extra weight and hindrance caused by T-shirts.


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