INTO THE DEEP WITH A SPEARGUN

A UNIVERSAL DISCIPLINE OF UNDERWATER SPORT

...Summer. The blue-silver swell of the sea. Here and there snorkels glint, here and there fins flick up like dolphin fins — a spearfisher has dived into the depths after his quarry. Now he descends into the grey-blue depths, to the bottom, and slips lightly and silently from rock to rock toward a small patch of open ground where a school of fat flathead mullet is grazing. One more stealthy dash forward, one more pass through an underwater cave, and the fish is within range. He is already longing to breathe, but slowly the speargun reaches forward. The spear flashes like lightning and pierces a large rounded body with big pearly scales. A short struggle at the bottom — and the fish is in the athlete's strong hands. A wave of joy washes over him. He shoots up to the surface and greedily breathes in the sea air. He has won a tough duel...
Sport underwater shooting (SUS) is a thrilling, fascinating pursuit that demands good physical and specialised athletic training and a knowledge of many of the sea's secrets.
Sport underwater shooting is not just shooting fish but something more interesting and substantial — it is a sport, a form of multi-event competition in which shooting fish is one of the events. Admittedly, the hardest one. Like any other sport, it has established Rules and Regulations for competitions and its own sports ranking system, from third class up to Master of Sport of the USSR. The new sport has a specific system of athlete training and a set of compulsory exercises, mastering which not only gives a person the opportunity for physical improvement and spiritual development but also, like any other collective activity, places certain social obligations on them and fosters and develops a sense of comradeship.
SUS can and should be practised all year round, perfecting one's athletic skill and developing one's physical and physiological capacities. And the fact that SUS has become a recognised discipline of underwater sport is of great significance for physical culture. The Rules and Regulations for the new sport, approved by the Central Committee of DOSAAF of the USSR, provide for special exercises for underwater shooting athletes that can be performed in swimming pools. For pool competitions at any time of year, two exercises have been developed and approved: shooting at a stationary target, and shooting at a moving target after first passing through a system of underwater obstacles.
In creating these exercises, the goal was to make them sufficiently challenging and interesting as a sport to draw many thousands of young people to the pools to take up SUS. The exercises are designed so that their component elements can be used to cultivate and train specific physical and volitional qualities in the athlete, and so that performing them in pools gives a person genuine sporting satisfaction.
In other disciplines of underwater sport, Soviet athletes have no equal in the world. Our task is to ensure that Soviet underwater shooters, too, worthily represent their country's underwater sport in international waters.
To assume that sport underwater shooting is the easiest of the underwater sports would be a serious mistake. Shooting underwater is, on the contrary, the highest school of human conduct during a free dive, the highest school of understanding and using the capabilities of one's own body in the aquatic environment. Mastering SUS requires all the basic physical qualities and strength of will that are cultivated and developed in other underwater sports — speed of movement in kit No. 1 on and under the water, instant orientation, endurance and physical strength, agility, courage and composure, a sense of comradeship and collectivism, skill in handling a weapon, and a deep knowledge of the theory of underwater sport. One must also be able to use underwater equipment, including scuba gear and wetsuits, since every athlete must be capable of thoroughly studying the underwater terrain of the waters where future competitions or training will take place, and of giving emergency help to a comrade in trouble underwater.
Thus, without any exaggeration, one can say that sport underwater shooting is a universal discipline of underwater sport, cultivating the most diverse physical and spiritual abilities and qualities in a person.

MAN UNDERWATER
The underwater world has long drawn people to it. But probably from the very moment our distant ancestor first stepped into the water, he sensed and understood that the aquatic environment differs from the air, and that normal functioning in this environment is impossible for a land creature.
Even the movement of the body on the water and through the water is considerably hampered. This is because water is 775 times denser than air. Its specific gravity is 1 g/cm3. To compare the weight of water with the weight of air, just imagine that a column of air as tall as the entire thickness of the Earth's atmosphere (traces of the atmosphere have been detected at altitudes of more than 1000 km) weighs (presses on the body) as much as" a column of water only 10 m high. The density and specific gravity of water determine the force with which it acts on a body immersed in it. This is called hydrostatic pressure.
When diving, the body of an athlete-diver experiences dynamic (constantly changing) hydrostatic water pressure, which causes certain physical and physiological changes in the human body. That is, water pressure has a direct, mechanical, and an indirect, biological, effect on the human body.
Despite its considerable magnitude, hydrostatic pressure is not dangerous to the human body, because our body consists of almost 70% fluid, which, as is well known, is practically incompressible and responds to the water pressure with an equal counterpressure. However, the human body has cavities filled with air, which is subject to compression and a decrease in volume under pressure according to the Boyle-Mariotte law. These are the lungs, the middle ear cavity, the maxillary sinuses and frontal sinuses, and sections of the intestine. The largest volume of air is held in the lungs, which serve as the "compensating reservoir". In a healthy person, the paranasal sinuses and the middle ear are connected to the lungs by air-conducting channels and passages. During a dive with a supply of air in the lungs, the lungs are compressed under the increasing pressure of the surrounding water (by 0.1 atm for every meter of depth), and the air in them at each given moment

Fig. 1
is under a pressure equal to the pressure of the surrounding water. Through the air-conducting passages, the rising pressure, in the form of a certain amount of compressed air, also penetrates all the other cavities. Into the middle ear, in particular, compressed air from the lungs enters through the Eustachian tubes.
Every diver has felt pain in the ears when descending, and this often scares a beginner away for a long time from any further attempts to dive more or less deep. It is the result of water pressure on the eardrums.
The whole point is that the Eustachian tubes are normally closed. To move additional air into the middle ear, it has to be forcibly "blown" through the Eustachian tubes. The mechanics here are simple: the water pressure bends the eardrum inward (Fig. 1,a), while the air that has come from the lungs and compensates the volume of the middle ear cavity creates a counterpressure equal to the hydrostatic pressure, and the eardrum returns to its normal position (Fig. 1,b).
Ways of "clearing" the ears are individual. For some divers it is enough to swallow, others exhale a little air into the mask, and a third group, the majority, have to pinch their nostrils through the mask, pressing its lower edge against the nose, while exhaling forcefully through the nose to push air into the ears. In very few people do the Eustachian tubes let air through freely; for them the pressure equalizes on its own, with no extra effort at all.
If you do not "clear" in time and keep descending, overcoming the pain, the eardrum will be pushed inward. If, however, you cut off the water's access and pressure on the eardrum from outside (by making, say, hard caps for the ears), then during the descent air under increased pressure from the lungs will enter the middle ear cavity, and the eardrum may then be ruptured by pressure from within. A ruptured eardrum is possible only in beginners, out of basic ignorance or recklessness, from ignoring the warning signs of pain. When you have a cold, which often happens in the first days at the sea, the mucous membrane of the Eustachian tubes swells and their patency drops sharply; diving in that case is not allowed.
If you feel you cannot "clear" during a dive, surface immediately and try doing it at the surface. If it works, repeat the dive. If your ears will not "clear", diving must be stopped until the patency of the Eustachian tubes is fully restored.
...If the eardrum has burst nonetheless, meaning an ear barotrauma has occurred, you must get out of the water immediately, wipe away any blood, limiting yourself to the outer ear and not going into the ear canal, apply a dry sterile dressing, and gargle with warm water with 3-4 drops of iodine per 1/2 glass or with a weak potassium permanganate solution. Do not blow your nose. See a doctor immediately. Usually, if no infection has got into the wound, the eardrum heals in a week and a half to two weeks. But infectious complications are not all that rare. Remember that through carelessness and ignorance you can not only lose a significant percentage of your hearing but also part with the underwater world forever!
The external air cavity for a diver is the space under the mask. The air under the mask is also subject to compression. Here the resistance of the rubber the mask is made of does not let the air compress to the necessary volume and reach a pressure equal to the surrounding one. At some point during the descent there is not enough air under the mask, and the pressure there becomes lower than in the surrounding water and in the tissues of the face. The mask starts to suck onto the face, much like a medical cupping glass. This can cause hemorrhages in the subcutaneous tissue, rupture of the tiniest blood vessels in the eyes, and nosebleeds. It is easy to avoid: at the very first sensation of vacuum you just need to add, to "blow" air into the mask through your nose. That is exactly why sealed goggles that do not cover the nose are unsuitable for deep diving.
A spearfisher should remember, however, that the larger the viewing glass of the mask and the larger the volume of the space under the mask, the more compensating air from the lungs will be needed to equalize the pressure there. When diving to depths of just around 10 m, the air spent (it is twice as dense here) on equalizing a large mask can noticeably shorten the time the diver spends underwater. So when choosing a mask for spearfishing, you should keep in mind the optimal ratio between the size of the glass and the volume of the space under the mask.
The thermal conductivity and heat capacity of water are substantially different from those of air. In water, even if its temperature equals the air temperature, a person cools down much faster. The reason is that the thermal conductivity of water is about 25 times greater than that of air. To retain body heat for a long time while in the water, divers use various wetsuits. They will be discussed in the corresponding section of the book.

LIGHT, COLOUR AND SOUND UNDERWATER AND WHAT THEIR TRANSFORMATION MEANS FOR THE SPEARFISHER
Light travels through water in a fundamentally different way than through air. Even the clearest water transmits light roughly 1000 times worse than air. A layer of distilled water just 1 m thick absorbs more than 10% of the sun's radiant energy. How deep light penetrates into the water column depends largely on the angle at which the sun's rays strike and on the state of the water surface. The more vertical the sun's rays, the more light reaches the depths. The lower the sun and the sharper the angle of incidence, the more radiant energy is reflected off the surface of the sea and goes back into the atmosphere. At a certain angle of incidence, all of the ray's light energy is reflected by the water surface. A light, fine ripple increases the illumination underwater.
For the spearfisher, however, midday light is by no means the best. Bright rays cause an equally bright reflection off suspended particles, and all the water takes on a murky golden tint that badly reduces visibility. Besides, the absence of shadows from rocks and stones in the middle of the day makes it harder for the spearfisher to move unnoticed along the bottom and to set up ambushes near the bottom.
It is worthwhile for the spearfisher to have an idea of how human vision adapts to lower light levels. We know from everyday experience that the eyes are able to adjust to changes in light intensity. To see better in semi-darkness, the eyes need a certain amount of time. This adaptation can be sped up with some preparation.
If a spearfisher is shooting underwater at a depth where light is low, he should not lift his head and look at bright light before the dive. Moreover, while resting and hyperventilating before the dive, it is useful for him to close his eyes and spend at least some time "in the dark". His underwater vision will then be sharper. A visor made of dark-red acrylic glass, fixed above the mask glass and shielding the eyes from direct sunlight and the glare of the sea surface, will speed up the eyes' adaptation to the low light of the depths.
Water acts as a blue light filter, and the thicker the layer of water, the denser the filter. All colours change with depth. For example, red becomes burgundy at a depth of about 5 m, then gradually turns brown as you go deeper, and beyond 12 m reds increasingly turn dark green. At 20-30 m all colours are bluish-grey, monotonous and dull...
A diver should know that if he injures himself at depth, he will not see red blood and may not notice that bleeding has started. All the more so since pain is noticeably dulled in sea water. A large loss of blood may go unnoticed.
Sound travels through water at tremendous speed - more than 1500 m/sec. That is almost five times faster than sound waves travel in air. On land sound is conducted mainly through the air, and in water mainly through the bones. That is, while at the surface sound is air vibration picked up by the eardrum, in water sound waves are perceived mainly by the bones of the skull.
How far sound travels in water depends not only on its strength but also on its spectrum. Scientists know for certain that the high part of the spectrum fades faster in water than the low part. As for how a person perceives sound in water, things are probably different. Practice shows that an underwater swimmer hears high sounds better. Just remember that the incredibly rich world of sounds with which the blue depths literally ring when we sit quietly in ambush - sounds resembling little bells, metal balls clinking against each other and so on - is precisely a world of very high sounds! There is no scientific data on this question yet; hydroacousticians are only just studying the problem.
All kinds of motor vessels pose a great danger to a spearfisher training at sea. It is not unusual for a diver on the bottom to suddenly hear the growing noise of a motor vessel. He is afraid that when he surfaces he will end up under the propeller blades or under the hydrofoils. In this case it is very important not to panic, not to rush, but to listen and try to analyse the sound. Based on many years of experience, we can say that the vessels most dangerous to a diver - hydrofoil boats - send mainly a high, continuous sound underwater, probably because the hull itself, acting as a low-frequency resonator, is lifted out of the water. Hydrofoil vessels become clearly audible underwater only when they are already relatively close. This increases the danger. If a high sound suddenly appears and grows in strength, we advise not surfacing (if possible) until the sound starts to fade. If you cannot stay underwater, then when you surface, take a quick breath and at the same moment instantly look around, and if necessary dive again... A low, dense, booming sound indicates a large ship moving in the distance. A knocking motor sound of a lowish spectrum indicates a motorboat; the strength of the sound tells you the distance to it. Attentiveness and practice will over time teach you to determine underwater the distance to a moving vessel and its type. In any case, however, if you hear a sound, stop a metre and a half below the surface and look around.
It is harder to determine where a sound source is and in which direction it is moving. At the surface a person determines the direction of a sound because the sound wave reaches one ear (the nearer one) first and then the other. This difference subconsciously gives the angle at which the wave arrives. In water, however, sound travels so fast that it is very hard to catch the difference in when the wave reaches different parts of the skull. The error can be a full 180°. Experiments show, however, that long training does make it possible to learn to determine the direction of a sound source fairly accurately.

MEDICAL AND PSYCHOPHYSIOLOGICAL REQUIREMENTS FOR THE ATHLETE - THE UNDERWATER SHOOTER
The physical and physiological features of underwater sports in general, and of competitive underwater shooting in particular, demand of a person excellent health, good and stable endurance under heavy physical strain, psychological preparedness for working underwater, a balanced nervous system, emotional stability, quick reactions and resourcefulness, powers of observation and self-control*.

* The medical requirements for underwater athletes, including underwater shooters, are set out in the "Schedule of Diseases and Physical Defects Precluding Participation in Military-Technical Sports" (Appendix 1 to the "Regulations on Medical Support for Military-Technical Sports", approved by the Ministry of Health of the USSR and the Central Committee of DOSAAF of the USSR in 1972)

Handling underwater weapons with great striking power requires not only good physical fitness but also a serious attitude. Therefore, young people who have reached the age of 16 should be admitted to training in competitive underwater shooting and to competitions in pools, while only athletes who have reached the age of 18 should be admitted to competitions in natural waters, owing to the heavy physical and psychological loads.
The athlete - underwater shooter must be free of "fear of enclosed spaces" and be able to assess a changed situation quickly, calmly and correctly, and must under no circumstances lose his head in an emergency or give in to panic; that is, he is a person of bold and decisive character, confident in his abilities, yet at the same time able to judge correctly the capabilities of his own body.
Most of the trouble and misfortune athletes run into comes from excessive self-confidence, recklessness and record mania - the urge to dive deeper, farther, and stay underwater longer than others at any cost, and so on. The main enemy is getting carried away. The main friends are a sober mind and a correct assessment of one's own strength. All these physical abilities and traits of mental make-up must be kept in mind in the medical and psychophysiological selection of future athletes, and in their training and upbringing.
Many of the physical and psychological qualities named here that an underwater shooter needs come, as a rule, only with experience, training and age. These include, for example, endurance under heavy physical loads (say, when spending six hours a day, two days in a row, in and under the water at competitions in natural bodies of water), mental balance, composure and resourcefulness (which is nothing other than experience put into practice), the absence of a sense of danger when working at considerable depths, and finally, the development of a wide range of techniques for carrying out complex underwater tasks and knowledge of the habits and way of life of various underwater creatures. As the practice of competitive underwater shooting convincingly shows, success always goes to people who are physically and spiritually formed, to mature people.
With the start of the mass and official promotion of competitive underwater shooting, and with the introduction of a set of exercises into the training and competition programme, competitive underwater shooting began to "get younger".

FREEDIVING IS THE CORE ELEMENT OF THE UNDERWATER SHOOTER'S PHYSICAL ACTIONS
If you do underwater touring or underwater orienteering, speed swimming with scuba or speed finswimming, in all of these cases the problem of air doesn't concern you. You carry it with you in the scuba tank, or you breathe atmospheric air through a snorkel. Even in speed apnea with set No. 1 (men - 40 m, women - 25 m), the main and only goal is speed of movement, not how long you hold your breath. An average second-class athlete covers 40 m underwater in 22-25 sec. And it is only for this comparatively short time, albeit at maximum physical exertion, that he has to hold his breath. The sporting tasks and objectives of the speed athlete and the underwater shooter differ substantially. The speed athlete strives to develop full power and reach maximum speed of movement in order to cut down the time spent underwater. The shooter, on the contrary, most often strives to save effort and to extend the time of his actions underwater as much as possible. This is especially the key prerequisite for successfully performing the most difficult exercise - shooting at moving targets in natural waters.
In none of the previously existing kinds of underwater sport does success depend on an individual's ability and training to hold the breath for a long time. In the main training and competition exercises of sport underwater shooting, it is precisely the ability to voluntarily hold the breath for a considerable time while staying physically active underwater that success depends on. The free dive on a held breath, i.e. with a supply of air in the lungs, is the main element on which all the techniques, methods and variations of performing the training and qualifying exercises of sport underwater shooting are based and developed. In other words, sporting success depends to a large extent on how well the athlete has mastered the technique of the free dive and of moving underwater, how well he has trained his own body, and how economically he has learned to use the oxygen stored in his blood and lungs.
The first official Moscow winter championship in sport underwater shooting, held in early April 1972, attracted many novice athletes. All of them performed poorly. And the main reason was precisely that most of them, even in simple pool exercises, didn't have enough time to cover the underwater distance and then carefully aim at the target. As a rule, they were in a great hurry to surface and take a breath, and felt extremely constrained underwater. Hence the fussiness, the feverishness and anxiety in their movements, the lack of precise orientation and body stabilization, breaking the firing line, hasty shots and misses.
Experienced athletes acted quite differently. After all, even the third exercise - shooting at a moving target - took 25-35 sec. Every good underwater shooter is able to hold his breath on a dive for 1.5-2 min. This reserve of "freedom" underwater gave them a clear advantage: a feeling of complete ease, measured and smooth movements, the chance to unhurriedly stabilize the body at the firing line, check the position of the gun and the spear line, etc., calmly and carefully take aim and smoothly squeeze the trigger. Of course, much also depended on other factors, for example, the quality of the gun, but the decisive factor was still mastery of the free-dive technique.
The ability to hold the breath for long enough is even more necessary when performing the third exercise in natural conditions, at sea, where a person underwater goes one-on-one with a fish.
Further on we will look at all the phases of the free-dive technique and at methods of breath-hold training. Here we will only get acquainted with the initial and final moments, which are most closely related to the physiology of the free dive.
Preliminary hyperventilation (intensified ventilation) aims to remove as much as possible, to "wash out" from the body, carbon dioxide - the natural stimulant of the respiratory center (see below), and also to slightly increase the oxygen content of the blood. And it is precisely this that allows the athlete to increase breath-hold time. The volume of a person's lungs is roughly 6 l. During breathing, only about 0.5 l of air enters the lungs with each breath. This air is called tidal air. If you take a maximal breath, another 1.5 to 3 l of air will enter the lungs, depending on lung capacity and the person's fitness. This air is called complemental air. After a normal exhalation, with extra effort you can push another 1 to 2.5 l of air out of the lungs, which is called reserve air. And finally, even after such a maximal exhalation, up to 1.5 l of residual air will still remain in the airways and lungs. The entire volume of air, excluding the residual, is called the vital capacity of the lungs.
Under normal conditions, breathing is regulated automatically in humans and is carried out by a group of nerve cells in the brain called the respiratory center. We know that external respiration is the enrichment of the blood with oxygen and the removal from it of a breakdown product - carbon dioxide*.

* So-called internal respiration refers to the processes of gas exchange in the tissues.

The respiratory center is very sensitive to a rise in the concentration of carbon dioxide in the blood and to a drop in oxygen content. And our urge to take a breath of fresh air is nothing other than a signal from this center that there is too much carbon dioxide in the blood and not enough oxygen. At the same time, our breathing unconsciously becomes faster and deeper.
Hyperventilation is forced deep breathing with maximum replacement of the air in the lungs with each breathing cycle. When hyperventilating, you need to breathe so that the entire vital capacity of the lungs is used. Hyperventilation technique is to a certain extent individual. However, the optimal option, found as a result of research, is considered to be 8-10 deep breaths per minute with a full exhalation, and a maximum inhalation before the dive. With properly performed hyperventilation, at the end of it the athlete feels a light and pleasant sensation of "floating" in the head. After that he takes a final full breath and dives. For the first 10-20 sec. the athlete feels an excess of air in the lungs and wants to exhale a little. This should not be done, because this sensation gives way to a feeling of optimal balance, when you want neither to inhale nor to exhale and "it could be like this forever". This state, depending on whether you are lying in ambush or moving actively, lasts from 20 to 60 sec. Then the first, still weak, urge to breathe appears, which intensifies fairly quickly. This is the signal to return to the surface calmly and without haste...
Somewhat different in physiological character is the cleansing, subsequent ventilation of the lungs, performed immediately after returning to the surface. This is the active removal of the carbon dioxide accumulated in the blood and the replenishment of the oxygen deficit that arose during the dive. However, this ventilation should not be hyperventilation, i.e. forced intensive breathing with maximal exhalations and inhalations. During cleansing ventilation you can alternate deep but free and slow breathing with frequent, shallow and light breathing. Subsequent ventilation is always calm breathing, with pleasure and without any strain, at the rhythm and volume of breaths that feel pleasant to the body. The next hyperventilation before the following dive may be done only when breathing has fully calmed down. For a well-trained person, 2-3 min. is enough for this, depending on how long they have been working. Such is the normal physiological cycle of breath-holding and recovery in free diving.
Free diving to depth, when done incorrectly, with insufficient experience and knowledge, poor training or overtraining, can lead to disruptions of the body's normal vital processes. Breath-hold diving also has its own dangers, which an athlete who is an underwater hunter needs to know well.
A free dive is intense physical work by the athlete, performed during a prolonged breath-hold in the water. Intense work in the water and the activation of oxidation processes lead under these conditions to a sharp drop in oxygen content and a rise in carbon dioxide content in the blood. Cooling of the body in the water, especially in its near-bottom layers, while diving without a wetsuit further intensifies the consumption of oxygen by the body's tissues, which leads to the rapid development of oxygen deficiency.
The first disruptions can arise even before the dive. Prolonged and intense hyperventilation leads to a sharp decrease in the carbon dioxide tension in the blood - hypocapnia. An inexperienced person, striving to breathe up as much as possible, sometimes exceeds the strict norms of useful ventilation. Intensified hyperventilation, already at 15-20 inhalations-exhalations, can lead to the phenomenon of apnea - an involuntary cessation of breathing. The cause of apnea is that the carbon dioxide content in the blood becomes insufficient to stimulate the respiratory center of the brain to send impulse-commands to the muscles that carry out the breathing process. Apnea occurring on land is not dangerous, and as soon as the normal carbon dioxide content in the blood is restored, breathing will resume. Apnea in the water is dangerous because at its end acute oxygen starvation of the brain may develop, with loss of consciousness. On land, consciousness returns once breathing is restored; in the water this can lead to a tragic outcome. As Soviet and foreign research* and experiments show, hyperventilation of the lungs before a dive should not exceed GO-90 sec.

* On the pathophysiology of the free dive, see the articles by Candidate of Medical Sciences V. I. Tyurin in the collection "Sportsmen-podvodnik. Moscow, DOSAAF Publishing House, No. 21 - 1969, No. 24 - 1970, No. 25 and 26 - 1971.

Exceeding these norms leads to undesirable consequences. Dizziness, confusion, and impaired coordination of movements during hyperventilation are a clear sign of overventilation - hyperpnea - which may be followed by apnea. But apnea sometimes occurs without any warning signs at all.
Especially favorable conditions for the onset of oxygen starvation are created when diving to depths exceeding 12-15 m. The reason for this is that at depth, where the air in the lungs is under increased pressure, the partial pressure of the oxygen contained in the air also increases. Therefore, while at depth, the diver does not feel oxygen deficiency for a long time. But when he begins to return to the surface, the oxygen content in the blood will drop rapidly, not only due to its consumption by the body, but mainly as a result of the sharp drop in its partial pressure in the air in the lungs, owing to the drop in the total air pressure.
As an example, let us take our maximum depth of 15m and a well-trained athlete-diver who has an excellent command of hyperventilation methods and diving technique. It is known that the partial pressure of a gas (p) is determined by the formula

p = P* a /100,
where P is the total (absolute) pressure of the gas mixture and a is the percentage of the given gas in the mixture. Atmospheric air contains a little over 20% oxygen. The partial pressure of oxygen in air at sea level will be:

Po2 = 760*20/100 = 152 mm Hg
Alveolar air usually contains 14-15% oxygen; after hyperventilation its content can rise to 16-17%. Having hyperventilated, the diver descended to 15 m, spending a certain amount of energy and oxygen in the process and lowering the oxygen content of the alveolar air to roughly 12-10%. After some time (in our case, too long!) at that depth and after performing some actions, the oxygen content in the alveoli dropped to 4%, and its partial pressure fell very state of oxygen starvation in well-trained people sets in at the surface when the percentage of oxygen in the alveolar air drops to roughly this value, and its partial pressure then equals

Po2 = 760*4/100 = 30.4 mm Hg
But that is at the surface. At a depth of 15 m, at a pressure of 2.5 atm (or 1900 mm Hg), the partial pressure of oxygen in the alveolar air will be:

Po2 = 1900*4/100 = 76 mm Hg
i.e. 2.5 times higher than under the same conditions at the surface. And the diver will feel as if his alveoli held not 4% oxygen but 10%! That is, still quite fine, considering that 10% is two thirds of the normal content. The danger comes on the ascent. Already at 10 m the partial pressure of oxygen in the alveolar air will drop to 60.8 mm Hg, at 5 m to 45.6 mm Hg, and at the surface to 30.4 mm Hg. Which corresponds to a 4% content. This is the critical value. But in our case it will be much lower still, because we did not take into account the ongoing oxygen consumption of the ascending diver's body. Coming up from 15 m, he "burned" it more intensively than on the descent, for about 15 sec., and the oxygen content of the alveolar air would actually have fallen to 1-2%! Loss of consciousness from oxygen starvation is inevitable in this case. That is why you must dive to depth correctly and competently.
The most dangerous phase of a breath-hold dive is the ascent. A sensible diver going to significant depth always remembers this and starts heading for the surface well before the "last bell".
According to V. I. Tyurin, a physiologist and specialist in the physiology and pathophysiology of underwater sports, oxygen starvation can develop faster in unfavourable external conditions that demand great physical effort: in currents, in rough seas, with strong positive buoyancy of the diver when the dive was made with effort, or, conversely, when overcoming considerable negative buoyancy at the start of the ascent from the bottom, etc. The development of oxygen starvation — this main danger of breath-hold diving and the chief cause of fatal outcomes — is also promoted by insufficient training or overtraining, a sleepless night, prior severe fatigue or alcohol intoxication, and so on. As V. I. Tyurin convincingly shows, it is not only beginners who die from oxygen starvation, but experienced divers too. The French and world spearfishing champion Jules Corman, the Portuguese champion José Ramelata and others have died. What is the cause? Most likely oxygen starvation and overestimating one's strength and the physical and physiological capabilities of the body, plus success going to one's head.
All depth-diving competitions in our country have been banned since 1934. Men are allowed to dive to 15 m, women to 10 m. All organisers of mass sport underwater shooting competitions, instructors and team coaches need to know this.

EQUIPMENT AND WEAPONS OF THE UNDERWATER SHOOTERSET No. 1 - FINS, MASK, SNORKEL AND HOW TO CHOOSE THEM
Over 15 years of underwater sport development in the USSR, many different models of fins, masks and snorkels have been produced.
Fins should be chosen mainly according to athletic preparation and physical build. The experience and practice of competitions and training also suggest that while the underwater biathlon exercises in the pool call for one type of fin, exercise No. 3 in natural waters is better done with fins of somewhat different characteristics. In the first case all attempts of the exercise are completed in 6-8 min. Here the athlete should have sufficient speed and the ability to perform fairly complex manoeuvres underwater, mainly using the legs. In this case the fins should have a large working surface and be relatively stiff.

For performing sport underwater shooting exercises in pools, the closed-heel fins of Moscow Plant No. 4, model No. 6 (fig. 2,а), are suitable, as are the "Amfibiya" fins of the Leningrad plant "Krasny Treugolnik" (fig. 2,6). But model No. 6 fins have a narrow foot pocket that squeezes the foot in its middle, outer part; with prolonged use, painful cartilage-like swellings form at the pressure points. For this reason the inner cavity of these fins has to be widened by hand.
At competitions some athletes use homemade elongated speed fins. This is hardly advisable: such fins are used to increase speed in a straight line, and it is difficult to maneuver in them.
Exercise No. 3 in natural bodies of water is performed for 5-6 hours on each of the two days. Here the athlete dives much deeper, with greater physical exertion and for an incomparably longer time. For performing this exercise at sea, more flexible, "non-tiring", yet still sufficiently powerful fins are preferable, ones that would let the athlete avoid excessive leg fatigue while at the same time allowing a quick descent, a swift dash underwater to grab the fish by hand and not let it slip off the spear, or, in the brief seconds when the fish has gone behind a rock, to move across and cut it off, and so on. For the complex and varied tasks of this exercise, the most suitable are the closed-heel fins of Moscow Plant No. 4, model No. 7 (fig. 2,в), the Kiev plant's "Akvanavt" model fins (fig. 2,г), and also the closed-heel fins of the "Vulkan" plant, "Delfin" model (fig. 2,д).
In lakes and rivers, at comparatively low water temperatures, athletes perform this exercise in "Sadko"-type dry suits with rigid soles.Fig. 2
In this case it is convenient to use semi-open models of fins with an adjustable heel strap, or the Moscow-made "Tyulen" model fins, designed specifically for dry suits, with a cut-out heel and lacing (fig. 2,е). The hydrodynamic characteristics of these latter fins meet the requirements of lake and river conditions.
A well-trained athlete uses fins that are more powerful, heavier and stiffer. They give his movements greater speed and sharpness. A beginner spearfisher's legs will tire in such fins within the first 10-15 minutes. In this case cramps of the calf muscles are possible. Beginner spearfishers should use soft, light fins, in which they may lose some speed but gain in conserving strength. In all cases the fins must be fitted to the foot and must not pinch or chafe anywhere; tight fins cause cramps in the foot muscles.
The mask provides the shooter with the necessary field of view underwater; it has flexible rubber with a thin edge that fits snugly against the face, and a wide or split rubber strap that sits securely on the back of the head. It must have an optimal balance between field of view and

the volume of the space under the mask. The wider the field of view through the glass and the less air there is under the mask, the better. The domestic model that can be considered most preferable for sport spearfishing is the "Volna" mask made by Moscow plant .No. 4. It has excellent visibility, and because the rubber curves inward, the space under the mask is kept to a minimum; the mask has a very reliable clamp band for sealing the glass, ensuring it is completely watertight. But this model also has a few shortcomings, admittedly easy to fix in production. For instance, on most units the edge of the mask is rather thick and stiff; the pockets for pinching the nose from the outside are also rather crude, thick and narrow, i.e. they constantly squeeze the nostrils slightly from the sides. If you swim in this mask for a short time, these shortcomings go unnoticed, but if it stays on your face for several hours, clear red "scars" will be left on your forehead and cheeks, and your nostrils will hurt (fig. 3,a). Masks from the same plant with no particular name, article number 49 607, are also quite suitable for our sport. They have a good design and elastic rubber, a thin edge that fits snugly, convenient wide corrugated inward pockets
Fig. 3
for pinching the nose, and a fair field of view (fig. 3,6).
The "Buratino" masks from the same plant are also suitable; they have glass shaped like double goggles and a special molded nose piece (fig. 3,b). However, although the space under the mask is very small, their field of view is also rather limited. Another significant design flaw is that the glass, which has a deep notch for the nose, often cracks in half under the slightest accidental pressure. This mask must be handled carefully. Besides, the shape of the glass does not allow it to be held by a clamp band. A wire tie at the narrow part of the glass does not guarantee watertightness, especially with pressure changes.
Masks that cover the nose and mouth are unsuitable for sport spearfishing. They have a very large space under the mask and, as a rule, snorkels with valves, which are not always reliable and, most importantly, increase resistance when inhaling and exhaling, which makes ventilation harder.
Checking whether a mask is suitable is very simple. Place it on your face without pressing it and without putting on the strap, draw a little air in through your nose and take your hand away. A mask of the right shape and size will "stick" tightly to your face and won't let air in. A mask that doesn't fit your face or is of poor quality will let air in and fall off. You must not stop water leaking into the mask by tightening the strap. During long swims this will impair blood circulation in the head and leave marks on your face.
Many beginners try to use snorkels that are as long as possible, afraid of water getting in while swimming on the surface. But the longer the snorkel, the greater the total volume of "dead space"*, the larger the share of air excluded from active gas exchange, the more the resistance to inhaling and exhaling increases, the more time is needed for normal hyperventilation, and the faster the breathing muscles tire.

* "Dead space" ~ is the volume of the upper airways, trachea, bronchi and bronchioles. The air filling the "dead space" does not take part in gas exchange.

All the more so since you have to dive anyway, and water will inevitably fill the snorkel. There's no need to fear this; you should learn to automatically blow all the water out of the snorkel, down to the last drop, with your first exhale at the surface. And the shorter the snorkel, the easier this is. It is better to use snorkels no longer than 35 cm from the level of the mouthpiece, i.e. ones that barely rise above the back of the head while swimming.
The inner diameter of the snorkel should be no less than 18 and no more than 20 mm. A narrower snorkel will increase breathing resistance, while a wider one requires too much effort to blow all the water out after a dive. And finally, the snorkel should have as few bends as possible. When buying a snorkel, check that the mouthpiece is made of high-quality rubber and has a thin edge that doesn't rub the gums, with thin bite tabs that are held between the teeth. But even so, from clenching the bite tabs for a long time the spearfisher's mouth and jaws get noticeably tired. With regular swimming for many hours in set No. 1, this strain may have a negative effect on the spearfisher's teeth and gums. Many athletes believe that, with sport spearfishing being promoted as a mass sport in our country, industry should produce not only mouthpieces but also lip seals for snorkels. A lip seal would fit snugly around the mouth, leaving the athlete's jaws and teeth free and relaxed. Such a snorkel should have its own strap going around the head below the back of the skull.

WETSUITS AND DRYSUITS
The many hours that spearfishing competition events last in natural waters make it necessary to use diving suits even at the very highest water temperatures. Many companies in various countries that produce diving equipment make diving suits in a wide range of models. However, they all fall mainly into two groups: dry and wet. The former completely (sometimes except for the face and hands) isolate the body from contact with the water. The latter are not watertight; water gets through to the body, but because the suit fits snugly and the lining is fleecy, the water is hardly replaced, and, thanks to the air in the micropores, once it has been warmed by the body it retains that temperature for a relatively long time.
Drysuits are usually made of relatively thin rubber combined with rubberised fabrics. Thermal insulation is provided by the air held in the woollen diving underwear worn under the drysuit. Drysuit designs vary. Sometimes they are made as coveralls, top and bottom in one piece, and the diver gets in through an opening on the chest that is then sealed watertight. But more often such suits consist of a top with a hood, trousers with integrated boots, and gloves. Sealing is achieved either with inner and outer sealing rings or by tightly rolling up additional rubber skirts where the trousers and top join; the gloves and the cuffs of the top are sealed with rings that are rigid underneath and rubber on top (fig. 4).

Wetsuits are cut from a material created specifically for this purpose, a high-quality microporous rubber. The best models have a thick fleecy synthetic lining and are covered on the outside with a thin reinforcing synthetic knit fabric. Wetsuits usually consist of a jacket with a special strong, rustproof zip, trousers, socks, a hood and gloves. Sometimes there is also a vest. In some of the latest foreign suits the hood is made in one piece with the jacket, and the zip opens the top from below only up to the solar plexus. This design prevents water from being replaced at the most mobile spot, the neck. Depending on the water temperature and how long you expect to stay in it, a wetsuit can be used either
Fig. 4

in full or in part, for example wearing only the vest, or only the jacket with the hood, etc. For warm waters and swims of no more than 1-2 hours, one-piece wetsuits with short legs and short sleeves or no sleeves are very convenient (fig. 5).