Post by LSDeep on Dec 9, 2005 8:56:36 GMT -5
By Laura Harris
How many of you really know if your body is fully hydrated and ready for a dive? Fluid intake is one of the most important (but neglected) aspects of diving physiology and is something that you, the diver, have full control over. Hydration is one of the major players in the prevention of both DCI and soft tissue injury, so it is in your interest to understand what your body needs to perform to the max. There are few, if any references in the training manuals (entry level, advanced or technical) about fluid regulation and unless you have prior knowledge or a particular interest in fitness many divers remain blissfully ignorant about the importance of being properly watered. So here it is, the complete definitive guide to optimum hydration.
Physiology and water weight
Seven tenths doesn’t only apply to the water covering our planet, we have coincidentally the same ratio of fluid in our body. In fact between 69% and 72% of our total body mass comes in the form of fluids. Physiologically we have two types of fluid compartments, intracellular (inside cells) and extracellular (blood plasma, transcellular and interstitial fluid). Much of the water in our body is found in lean muscle mass. Interestingly, nitrogen appears to have a much lower affinity for water saturated tissue than for fat. Fat tissue holds five times more nitrogen than water permeable ‘aqueous’ tissue (such as muscles, ligaments, tendons and connective tissue).
We lose fluid through sweat, respiration, urination, diuretic action, stomach upsets and if you are female, menstruation.
In sports physiology, sweat loss is considered to be the most important aspect of fluid regulation. This is a factor that can be misunderstood and underestimated by divers. Our body fluid levels are intrinsically linked with our ability to sweat. Sweat is excreted as a result of heat production. Heat is a by product of muscular activity with about 75% of the energy expended during exercise being converted into heat. This extra heat has to be dissipated in order to keep our core body temperature a constant 37 - 38° C. Sweat is produced by some 3½ million sweat glands, when water from our body is carried via our blood capillary network to the skin, where cooling takes place as sweat evaporates.
We perspire in two different ways. Sensibly and insensibly. Sensible perspiration is sweat that is excreted in large amounts and is noticeably moist on the skin. Insensible perspiration is sweat that evaporates from the skin before it becomes moisture and we are therefore unaware of it. Normally, we start sweating on our foreheads first, then our face followed by the rest of our body with palms and soles of the feet last. Conversely, emotional sweat occurs in the palms, soles and armpits first. Incidentally, emotional sweat is relied upon in lie detector tests as even the smallest amount of perspiration contains sodium chloride which acts as an electrical conductor and therefore lowers the electric resistance of the skin. Both types of perspiration are important to a diver.
A ½ litre of water equates to about 1lb or ½ kg of body weight. It is possible to lose as much as 2lbs (about 1kg) of body weight through sweat in one hour performing normal aerobic type exercise, which in fluid terms amounts to about a litre. During high impact workouts or if you happen to be a person who sweats profusely, as much as 2 litres of sweat per hour can be lost.
Diving can be aerobic, anaerobic, stressful and emotional. Sweat production varies greatly during a dive depending on air and water temperatures, exposure suit, anxiety levels, currents, exertion, distance covered, whether you are male or female, individual fitness, experience and so on. Add to this the fact that divers breathe very dry air, are usually unable to replace fluids during a dive (unlike other sports), often dive in tropical destinations with high humidity, blast themselves on the sun-decks of liveaboards and it’s easy to see how dehydration sets in. If you are a cold water diver don’t think for a minute that you are immune ….. the morning after the night before, strong black coffee, cans of coke, mugs of tea and the limitations of peeing in a drysuit all conspire against you.
Most serious athletes know that a loss of only 2% of their body weight through sweating can reduce their aerobic performance by as much as 10%. In diving terms this fluid loss means less efficiency at off-gassing absorbed nitrogen. Blood becomes thicker and more viscous when it’s volume decreases through dehydration. Consequently blood flow is slowed which means the speed at which we eliminate nitrogen is reduced. The obvious danger becomes an increased risk of developing DCI. Other signs of dehydration include an increased susceptibility to headaches, fatigued muscles, dry or congested sinuses, gritty eyes, light headedness and nausea.
Dehydration - The facts
The first thing to understand about dehydration is that it is cumulative. How much or little fluid you take in over the days preceding a dive will have a dramatic effect on your hydration at the start of that dive and subsequent physiological performance. This means that a diver will be exponentially increasing their risk of DCI and soft tissue injury, through lack of fluids, over a consecutive series of dives, if this goes unchecked.
Without exception, we all wake up from a nights sleep in a state of dehydration. If you want to work out specifics, then weigh yourself last thing before going to bed (after consuming your last beverage) and again first thing in the morning (before drinking or eating). The weight loss is primarily fluid lost through overnight sweat and respiration (and any nightly visits to the toliet). Most of us will start the day about 1- 1½ litres down on our normal body hydration (known as euhydration). If you are planning an early morning dive, the chances are you will be doing the dive in a state of dehydration as it takes time and effort to fully rehydrate. Add to this the fact that you might be starting your diving soon after a flight and you are even further at a disadvantage as the atmosphere on aircraft is dry and of low humidity and is severely dehydrating.
So how do you know if you are dehydrated? Well, the easiest way is to check the colour of your urine. The stronger the yellow and the more potent the smell, the more dehydrated your body is. Ideally, urine should be plentiful, very pale yellow or almost colourless and odourless. However, there are exceptions to the rule and diuretic activity is one.
Diuretic Action
To understand how diuretics affect you as a diver it is worth knowing a little bit more about their nature. A diuretic is simply an agent, chemical or natural, that increases the rate of urine formation. The two most common diuretics that influence a diver are caffeine (found in coffee, tea cola drinks and chocolate) and alcohol. These two naturally occurring diuretics act on the body in an entirely different way but with the same end result - increased urine output (diuresis). Alcohol inhibits the secretion of Antidiuretic Hormone (ADH). Caffeine on the other hand inhibits sodium reabsorption. The diuretic action of these two substances is such that the net quantity of urine produced is greater than the actual amount of liquid consumed. Diuretics are therefore dehydrating. The resultant effect has a negative action on thermoregulation and cardiovascular function.
In terms of urine output and colour, the danger here is that urine colour can become diluted by the extra fluid sucked out of hydrated tissue, and visits to the toilet increase, leading to a false sense of security. That beer is roughly 95% water is of no consequence as this is more than offset by the alcohol content, so don’t kid yourself.
To counterbalance fluid lost through diuretic action a useful guideline is to additionally drink water, 1½ times the quantity of diuretic fluid either at the same time, or half an hour either side of intake.
How many of you really know if your body is fully hydrated and ready for a dive? Fluid intake is one of the most important (but neglected) aspects of diving physiology and is something that you, the diver, have full control over. Hydration is one of the major players in the prevention of both DCI and soft tissue injury, so it is in your interest to understand what your body needs to perform to the max. There are few, if any references in the training manuals (entry level, advanced or technical) about fluid regulation and unless you have prior knowledge or a particular interest in fitness many divers remain blissfully ignorant about the importance of being properly watered. So here it is, the complete definitive guide to optimum hydration.
Physiology and water weight
Seven tenths doesn’t only apply to the water covering our planet, we have coincidentally the same ratio of fluid in our body. In fact between 69% and 72% of our total body mass comes in the form of fluids. Physiologically we have two types of fluid compartments, intracellular (inside cells) and extracellular (blood plasma, transcellular and interstitial fluid). Much of the water in our body is found in lean muscle mass. Interestingly, nitrogen appears to have a much lower affinity for water saturated tissue than for fat. Fat tissue holds five times more nitrogen than water permeable ‘aqueous’ tissue (such as muscles, ligaments, tendons and connective tissue).
We lose fluid through sweat, respiration, urination, diuretic action, stomach upsets and if you are female, menstruation.
In sports physiology, sweat loss is considered to be the most important aspect of fluid regulation. This is a factor that can be misunderstood and underestimated by divers. Our body fluid levels are intrinsically linked with our ability to sweat. Sweat is excreted as a result of heat production. Heat is a by product of muscular activity with about 75% of the energy expended during exercise being converted into heat. This extra heat has to be dissipated in order to keep our core body temperature a constant 37 - 38° C. Sweat is produced by some 3½ million sweat glands, when water from our body is carried via our blood capillary network to the skin, where cooling takes place as sweat evaporates.
We perspire in two different ways. Sensibly and insensibly. Sensible perspiration is sweat that is excreted in large amounts and is noticeably moist on the skin. Insensible perspiration is sweat that evaporates from the skin before it becomes moisture and we are therefore unaware of it. Normally, we start sweating on our foreheads first, then our face followed by the rest of our body with palms and soles of the feet last. Conversely, emotional sweat occurs in the palms, soles and armpits first. Incidentally, emotional sweat is relied upon in lie detector tests as even the smallest amount of perspiration contains sodium chloride which acts as an electrical conductor and therefore lowers the electric resistance of the skin. Both types of perspiration are important to a diver.
A ½ litre of water equates to about 1lb or ½ kg of body weight. It is possible to lose as much as 2lbs (about 1kg) of body weight through sweat in one hour performing normal aerobic type exercise, which in fluid terms amounts to about a litre. During high impact workouts or if you happen to be a person who sweats profusely, as much as 2 litres of sweat per hour can be lost.
Diving can be aerobic, anaerobic, stressful and emotional. Sweat production varies greatly during a dive depending on air and water temperatures, exposure suit, anxiety levels, currents, exertion, distance covered, whether you are male or female, individual fitness, experience and so on. Add to this the fact that divers breathe very dry air, are usually unable to replace fluids during a dive (unlike other sports), often dive in tropical destinations with high humidity, blast themselves on the sun-decks of liveaboards and it’s easy to see how dehydration sets in. If you are a cold water diver don’t think for a minute that you are immune ….. the morning after the night before, strong black coffee, cans of coke, mugs of tea and the limitations of peeing in a drysuit all conspire against you.
Most serious athletes know that a loss of only 2% of their body weight through sweating can reduce their aerobic performance by as much as 10%. In diving terms this fluid loss means less efficiency at off-gassing absorbed nitrogen. Blood becomes thicker and more viscous when it’s volume decreases through dehydration. Consequently blood flow is slowed which means the speed at which we eliminate nitrogen is reduced. The obvious danger becomes an increased risk of developing DCI. Other signs of dehydration include an increased susceptibility to headaches, fatigued muscles, dry or congested sinuses, gritty eyes, light headedness and nausea.
Dehydration - The facts
The first thing to understand about dehydration is that it is cumulative. How much or little fluid you take in over the days preceding a dive will have a dramatic effect on your hydration at the start of that dive and subsequent physiological performance. This means that a diver will be exponentially increasing their risk of DCI and soft tissue injury, through lack of fluids, over a consecutive series of dives, if this goes unchecked.
Without exception, we all wake up from a nights sleep in a state of dehydration. If you want to work out specifics, then weigh yourself last thing before going to bed (after consuming your last beverage) and again first thing in the morning (before drinking or eating). The weight loss is primarily fluid lost through overnight sweat and respiration (and any nightly visits to the toliet). Most of us will start the day about 1- 1½ litres down on our normal body hydration (known as euhydration). If you are planning an early morning dive, the chances are you will be doing the dive in a state of dehydration as it takes time and effort to fully rehydrate. Add to this the fact that you might be starting your diving soon after a flight and you are even further at a disadvantage as the atmosphere on aircraft is dry and of low humidity and is severely dehydrating.
So how do you know if you are dehydrated? Well, the easiest way is to check the colour of your urine. The stronger the yellow and the more potent the smell, the more dehydrated your body is. Ideally, urine should be plentiful, very pale yellow or almost colourless and odourless. However, there are exceptions to the rule and diuretic activity is one.
Diuretic Action
To understand how diuretics affect you as a diver it is worth knowing a little bit more about their nature. A diuretic is simply an agent, chemical or natural, that increases the rate of urine formation. The two most common diuretics that influence a diver are caffeine (found in coffee, tea cola drinks and chocolate) and alcohol. These two naturally occurring diuretics act on the body in an entirely different way but with the same end result - increased urine output (diuresis). Alcohol inhibits the secretion of Antidiuretic Hormone (ADH). Caffeine on the other hand inhibits sodium reabsorption. The diuretic action of these two substances is such that the net quantity of urine produced is greater than the actual amount of liquid consumed. Diuretics are therefore dehydrating. The resultant effect has a negative action on thermoregulation and cardiovascular function.
In terms of urine output and colour, the danger here is that urine colour can become diluted by the extra fluid sucked out of hydrated tissue, and visits to the toilet increase, leading to a false sense of security. That beer is roughly 95% water is of no consequence as this is more than offset by the alcohol content, so don’t kid yourself.
To counterbalance fluid lost through diuretic action a useful guideline is to additionally drink water, 1½ times the quantity of diuretic fluid either at the same time, or half an hour either side of intake.