Static apnoea. Performance factors

Static apnoea

PERFORMANCE FACTORS

Text and photos ALEŠ KOŠTOMAJ

Competition in static apnoea

ABSTRACT Ever since the first deep diving competitions were organized, there has been debate about when the ultimate limits of human apnoeic performance will be reached, and which factors will determine these limits. Divers have thus far surpassed all former predictions by physiologists in depth and time. The common factor for all competitive apnoea disciplines is apnoeic duration, which can be prolonged by any means that increase total gas storage or tolerance to asphyxia, or reduce metabolic rate. These main limiting factors can be broken down further into several physiological or psychophysiological factors, which are identified in this article.

INTRODUCTION The word apnoea is derived from the Greek word a-pnoia and means “without breathing”. The very origin of the word has no connection with water but in modern terminology the word apnoea is used as a synonym for breath-hold diving or free-diving. This means submerging under water without additional external devices which would allow for breathing.

With practice, one can make progress in breath-hold diving very quickly. Unfortunately, the methods and strategies of such diving are less known in the scientific field i.e. to scientists and are difficult to explain because they are currently difficult to research in the aquatic environment with existing technology.

STATIC APNOEA Success in static apnoea depends solely on holding one’s breath, since a diver rests on a pool’s water surface in a relaxed manner. The ability of holding one’s breath is the basis of all other disciplines and methods of diving. There are three factors which determine the limit of holding one’s breath: 1. total amount of oxygen (O2) in the body (lungs, blood, and tissues); 2. ability to overcome hypoxia (deprivation of oxygen) and hypercapnia (excess of carbon dioxide); 3. metabolic rate.

Static apnoea

1. Total amount of oxygen in the body

lungs

Large lung volume has been repeatedly described as a differentiating factor among breath-hold divers. The usefulness of large lungs is known both in static apnoea as well as in deep dives or other deep disciplines. One study established the average vital lung capacity (VC) of 7.3 liters in 14 top divers which is about two liters more than in the control group’s subjects of similar age and body shape. The individual VC of top divers is related to their diving performance. This leads to the question of whether the enlarged lung volume is due to self-selection or whether it reflects the changes caused by practice. VC generally increases with growing up, however, numerous studies show that specific practice may increase VC. Other parallel studies also show high effectiveness of swimming practice and exposure to high altitude on lung volume.

influence of various breathing techniques

Lung packing (the glossopharyngeal insufflation maneuver) is a commonly used method to effectively increase lung volume. Normal maximal inspiration is determined by maximal contraction of the inspiratory muscles and thorax, and by lung compliance. By using the oral cavity and tongue to press small amounts of extra air down into the lungs, which are already filled with maximum inhalation, the diver can increase its volume by up to 4 liters. The disadvantage of this maneuver is the consequent increase in pressure in the lungs which reduces venous inflow and can lead to loss of consciousness if the diver does not dive in time. The extra volume of air will prolong apnoea by providing additional stored oxygen (O2) and by diluting the carbon dioxide (CO2) obtained from the blood. In combination with specific thorax stretching exercises, lung packing can also be used in practice as a method to increase lung volume. However, packing should not be the main mechanism for long-term increasing of lung volume.

blood

Blood is a liquid tissue whose function is, among others, to carry O2. It consists of the intravascular fluid or blood plasma, and blood cells. O2 and CO2 are transported via red blood cells or erythrocytes. The red blood cells are the most numerous among blood cells. Most of oxygen (98%) is carried bound to hemoglobin in red blood cells while a small part of it is dissolved in the blood itself. The amount of blood in diving mammals is higher than in other groups of mammals. In seals and sea lions, blood represents 10–20% of their body weight, while it amounts to only 7–8% in terrestrial mammals. Human blood volume can be increased by increasing plasma as an adjustment to endurance and heat training. The increase in erythrocytes will consequently have a small effect on the overall increase in O2 volume in the body. Short-term changes are caused by splenic contraction in apnoea and hypoxic respiration.

Top breath-hold divers have higher levels of hemoglobin in their blood than cross-country skiers and people not training. The reasons for that lie either in their practice of breath-hold diving or in their self-selection. The number of erythrocytes in blood is regulated via erythropoietin (EPO) which is produced by hypoxic kidneys. It is known that exposure to higher altitudes increases the production of erythropoietin. Less than a decade ago, however, it was shown that the erythropoietin

production is also increased by practicing breath-hold diving. With more intense and specific breath-hold diving practice and a diet high in iron, hemoglobin levels can be further increased, leading to higher capacity of O2 transport and CO2 removal. Breath-hold diving, and deep diving in particular, can cause stronger stimuli than altitude for erythropoietin formation.

spleen contraction

Spleens of diving mammals are an additional storage site for erythrocytes. This stock is activated with prolonged apnoea. Spleen contraction in humans Competition in static apnoea in apnoea was first observed in ama-divers (traditional breath-hold divers in Asia who collect pearls and shells). Less than a decade ago, it was found that the best breath-hold divers also have the largest spleens with a volume of up to 600 ml. The difference in contraction between the smallest and largest spleen in elite breath-hold divers corresponded to 30 s of apnoea duration. Spleen contraction is an active contraction process caused in part by hypoxia and not due to the diving reflex, as it requires multiple breath-holding dives to fully develop.

tissue

O2 accumulated in tissues is also an important source of O2 for aerobic metabolism. Tissues store only 2–3% of O2 which is stored in the body. It is the most abundant in myoglobin (Mb) in muscles. In marine mammals the levels of myoglobin can be 10 times higher than in terrestrial mammals. Myoglobin in muscles is important in all forms of breath-hold diving, in particular in dynamic disciplines (swimming distance).

2. Ability to overcome hypoxia and hypercapnia

phases of apnoea

The duration of apnoea depends on the ability to overcome hypoxia and hypercapnia. A mild respiratory response to CO2 has been reported in submarine rescue instructors, ama-divers, and underwater hockey players. In people who do not dive, however, CO2 is the predominant factor in stimulating respiration and stopping apnoea. Divers can tolerate higher levels of hypercapnia and hypoxia.

Apnoea is divided into two phases: the initial ‘easy-going’ phase without the necessity of inhalation, and the final struggle phase, in which the accumulation of CO2 is the main reason for the gradually stronger need for inhalation. The first phase lasts until the onset of spontaneous contraction of the respiratory muscles (the start of CO2 accumulation). Spontaneous contractions of the respiratory muscles cause discomfort and psychological burden, and as such also mark the boundary between the two stages of apnoea. The second phase, however, also depends on individual motivation and endurance. It has been shown, that long-term practice of apnoea affects not only the duration of apnoea but it also prolongs the duration of the first, initial phase.

The majority of inexperienced divers break the apnoea at the beginning of the struggle phase. Elite breath-hold divers distinguish as many as three phases of apnoea: the second struggle phase is followed by the third, fighting phase in which the desire to breathe is further increased by the combined stimuli of hypercapnia and hypoxia. In this stage, divers do not relax but use muscular strength to maintain apnoea. Developed psychological tolerance to strong contractions of the respiratory muscles in the last, fighting phase is crucial for successful static apnoea. It can only be improved with longterm practice.

Divers use hyperventilation in various forms to lower the CO2 content in the body and prolong the first phase of apnoea. However, hyperventilation represents an increased risk of loss of consciousness, as the O2 level does not increase to the same extent as the CO2 level decreases, and thus the risk of unconsciousness at the end of apnoea is increased. Hyperventilation is, therefore, not recommended.

hypoxia and brain function

Numerous studies show that practicing apnoea lowers the required level of O2 needed by the brain. During competition divers often experience a hypoxic loss of movement control and sometimes even lose consciousness, but they

quickly recover with the help of their safety diver. However, the question arises as to whether this causes any longterm damage of brain functions. Studies of neural functions of breath-hold divers have not shown bad long-term effects of apnoea practice on brain functions, which is thought to be due to regulation of protective stress proteins. At present there is no evidence that loss of consciousness in apnoea is harmful to the human brain. Many divers who partake in competitions know where their individual hypoxic limit is and that only prolonged apnoea training can move this limit towards a higher value.

3. Metabolic rate

The third limiting factor for the duration of apnoea is the intensity of metabolism. The lower the rate of metabolism, the lower the O2 consumption and the longer the apnoea can be.

cardiovascular diving reflex

Irving (1963) was the first to observe a diving reflex in humans. The first main effect of the diving reflex is the contraction of the blood vessels in muscles which are furthest from the lungs or brain (in fingers and toes). The other main effect is slowing down the heartbeat. Later it was established that there are, as a consequence, two additional effects: maintaining O2 and prolonging apnoea. The diving reflex is triggered by any apnoea. A complete reflex response can only be expected when immersing the face, especially the forehead and eyes. The diving reflex begins after only thirty seconds of apnoea. The diving reflex is not changed with multiple series of apnoea, but it is enhanced by prolonged apnoea practice.

temperature

The intensity of the diving reflex response is most influenced by water temperature. Colder water affects the response rate of the diving reflex. Warmer water, however, is more important for the duration of apnoea. Cold-blooded animals have their metabolic rate and O2 consumption connected to their body temperature. Mammals respond to lower body temperatures with faster metabolism and, above all, with shivering. When shivering, muscle cells use twice as much energy which in turn shortens apnoea. Anyone who can withstand a temperature drop without shivering will likely be able to perform a prolonged apnoea.

Ama-divers were once considered to be people who adapted best to colder water. Studies show that the use of neoprene suits has led to de-acclimatization. Better insulated individuals use less energy to shiver and allow the body to lower its temperature instead of wasting energy to keep the body temperature constant. Body temperature affects cardiovascular responses which are important for the length of apnoea.

Static apnoea

fasting and nutrition

Fasting is a method which is often used by divers to increase their diving performance. In terms of energy expenditure, fasting has been shown to reduce the resting metabolic rate by up to 17%. The best results in static apnoea can be achieved while fasting, which most divers already take advantage of in training and competitions. However, regardless of these findings, some breath-hold divers take carbohydrate supplements just before competitions to increase their performance. It is surprising, that while many top breath-hold divers consider their nutrition as extremely important, others ignore its significance.

relaxation techniques

In a sport where minimum oxygen consumption is more important than maximum oxygen consumption, it is obvious that relaxation techniques have a significant impact on results. This is especially evident in static apnoea. Special relaxation exercises with the emphasis on breathing techniques are derived from yoga and adapted for apnoea. Before competitions they are used by almost every top breath-hold diver. Yoga based cyclical relaxation techniques are expected to reduce O2 consumption by 32%.

CONCLUSION In comparison with untrained individuals, breath-hold divers can significantly increase the total volume of O2 in their body and the ability to overcome hypoxia and hypercapnia with regular practice. The metabolic rate can be reduced with special meditation techniques. At present, we do not yet have enough knowledge about the highest possible human potential in breath holding. However, some factors which influence its duration are already known in some marine mammals. These factors will have to be investigated also in humans. The best breath-hold divers believe that the maximum limit in static apnoea is somewhere around 15 minutes.

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