Muscles are the machinery that allows motion, not only of the limbs but of the whole body, including adjustment of the eyes to bright or dark environments, tuning of the eardrum, speech, swallowing, beating of the heart, regulation of blood pressure, motion of the intestines to allow digestion and many other functions. Every motion of the body is performed by muscles of one type or another. Muscles are usually divided into three types: skeletal, the muscle that forms the structure of the body; cardiac, which makes up the heart; and smooth, which makes up the structure of blood vessels, intestines, bladder, uterus and other organs.
Of the three, skeletal muscle represents the largest mass. Problems with skeletal muscles while diving usually center around fatigue, cramps and blunt injury. Failure of the leg muscles to function properly can cause difficulty swimming. The sensation of fatigue often leads to panic when a diver realizes the leg muscles are not capable of handling an unsafe situation.
Skeletal muscle uses both carbohydrate (in the form of glucose, a sugar molecule) and fat (in the form of fatty acids, the building block of fats) for fuel and is capable of functioning with or without oxygen. In the absence of oxygen, metabolism produces lactic acid and consumes glucose stores. When a muscle works without oxygen, the situation is labeled anaerobic. Working without oxygen produces lactic acid and is highly inefficient (12 times more energy is obtained from a molecule of glucose when oxygen is used) but, when rapid activity is needed, there may not be time to wait for oxygen to reach the muscle. When oxygen supply is inadequate, only glucose can be used to produce energy and it can be rapidly depleted. Muscles have adapted to this frequent imbalance between energy demand and supply by switching between fat and carbohydrate metabolism, based on oxygen availability.
At the beginning of exercise, muscles usually work anaerobically and produce lactic acid until circulation catches up and supplies enough blood to provide adequate oxygen. As exercise continues at a steady pace, the muscle begins to utilize more fat for energy, thus sparing the stores of carbohydrate held. If exercise is extreme, the muscles cannot get adequate oxygen and revert to anaerobic metabolism. The lactic acid produced by anaerobic metabolism eventually blocks the metabolism and the muscles develop severe spasms, felt as cramps. If enough oxygen is available, glucose is metabolized to carbon dioxide. Muscle fatigue occurs when the glucose stores are consumed and the muscle needs to work without oxygen (anaerobically).
Muscle fatigue and cramps can occur when the workload is too high to prevent anaerobic metabolism, when the blood supply is inadequate and when there is an abnormality that prevents normal metabolism. There are toxic substances that can impair muscle metabolism, the most common of which is alcohol.
By far, the most common cause of cramps is overuse of a muscle, for example, when a set of fins is too large. Fatigue of the leg muscles occurs when a diver tries to swim against a strong current and exceeds the limits of oxygen delivery; runners call this phenomenon 'the wall.' Inadequate blood supply can occur when extreme cold constricts the blood vessels or when disease of the vessels limits blood supply.
It is possible to improve the ability of muscles to withstand high levels of exercise by conditioning. Well-conditioned muscles adapt to high exercise states by increasing their ability to metabolize oxygen and by using more fat than carbohydrate during exercise. The conditioned muscle can reach higher workloads before becoming anaerobic, thus allowing steady exercise at a higher rate than an untrained muscle. The adaptation of muscle to exercise explains why swimming at a high workload can be tolerated better by a well-conditioned swimmer. The well-conditioned swimmer is less likely to get a muscle cramp, so avoiding fatigue and cramps is best accomplished by conditioning.
There are a few other causes of cramps that should be mentioned. When the level of potassium in the blood is low, cramps can occur. This is usually found in individuals taking diuretic medications and is rare in healthy people on no medication. Low levels of calcium in the blood can also cause cramps. Occasionally, the level of potassium and sodium in the blood are affected by severe sweating. In some individuals who work in hot environments and sweat profusely, cramps are often found accompanying a more severe condition of dehydration and heat exhaustion. Rarely, an individual inherits an abnormality in muscle metabolism. This is present from birth and most people are aware of it because they have muscle cramps throughout life.
To avoid cramps or muscle fatigue, avoid strong currents, follow a conditioning program to improve muscle capacity, avoid dehydration, hyperventilation and cold, avoid alcohol, maintain the health of your blood vessels by not smoking and by keeping blood pressure and cholesterol normal.
U/W Photography Competition in the Turks and Caicos: Divers/photographers visiting the Turks and Caicos Islands anytime up until October may enter the First World Open Underwater Photography Competition. It has two classes, one for professionals and another for amateurs. Winning entries will be reproduced by the Government of the Turks and Caicos as a set of commemorative postage stamps. Each stamp will bear the name and country of the photographer who took the picture.
Twelve honorable mention photographs will be published as a calendar. $10,000 in cash awards and up to $50,000 in additional prizes, including international dive travel, equipment and diving services, will be awarded to winners.
Photographers may submit up to five photographs and may work individually or as a team but prizes will only be awarded to individuals.
A selection committee will name the semi-finalists, then an international panel of judges will choose the eight winning photographs, four from amateur photographers and four from professionals.
Entries are due at the end of October; the prizes will be awarded in December.
Participants can obtain an entry form from the Turks and Caicos Tourist Board, by calling IDM International at (412) 487-1375 or from any dive operator on-island. Entrants must submit the form along with a $35 handling fee. In return, they will receive an information package and an official ID card that allows special discounts on air travel, diving services and hotels.
For further information or an entry form, contact Ralph Higgs, Turks and Caicos Tourist Board, Turks and Caicos Islands, British West Indies; (809) 946-2321, fax (809) 946-2733 or e-mail under cphoto@terraport. Visit the Underwater Photography Competition Web site at http://www.underwaterphoto.com.