Breath hold diving

I had a conversation with a friend today who was telling me about the Buteko breathing technique as a support therapy for those with asthma. She told me her husband’s ability to breath hold was quite substantial after he trained himself to breathe better. Buteko breathing involves training ourselves to breathe in through our nose and out through your mouth. The treatment is based on the concept that hyperventilation is the underlying cause of medical conditions such as asthma. It is known that hyperventilation can lead to low carbon dioxide levels in the blood (hypocapnea), which can subsequently lead to disturbances of the acid-base balance in the blood and lower tissue oxygen levels.

Although the research is sceptical of this treatment for asthma it could be beneficial to asthmatics as the function of the respiratory conduction system is to warm and humidify the air in order for the lungs to efficiently diffuse the gasses through the alveolar membranes. Asthmatics constantly complain that cold air can set off attacks.

We compared my friends husbands breath-hold performance to a free diver who can hold his breath for over 8 minutes – a little less but interesting nevertheless. I related the article I read about the “100m Man” William Trubridge (Scott, 2007) to her. I explained that his capacity for breath holding was related to his body’s ability to hold more air, his body’s efficiency for supplying O2 to his muscles and his ability to increase his ability to maintain his acid balance within his body and fight the urge to breathe. It’s also interesting that Trubridge warns to not use hyperventilation techniques before a breath hold dive as this can cause blackouts underwater and at the surface.

So how is Oxygen transported to the tissues?

Oxygen is carried in the blood. The Oxygen carrying component within blood is called haemoglobin. Haemoglobin carries four heme (iron) molecules, like pockets to carry O2, which oxygen binds to when they diffuse across the lungs alveolar membrane into the blood (McArdle, Katch and Katch, 2010).

So how does oxygen get off the haemoglobin train?

When the CO2 concentration gets to a certain level within the blood, this signals the heme to release the oxygen molecule. This is then diffused through the cells membrane and is consumed by the cell (Marieb and Hoehn, 2010). If the CO2 levels in the blood get higher the heme releases its second molecule and so forth. The article recalls Trubridges comments that this build-up of CO2 causes this overwhelming desire to breath which he has to resist.

So how did he do it?

The article states there are many things a free diver must overcome to hold their breath for large extended periods. There are things that both hinder and help a free diver. First of all he has to psychologically overcome the body’s desire to maintain homeostasis – this is the urge to breathe so it can lower the acidity of the blood by expelling CO2 via diffusion through the lungs to the atmosphere. Secondly the partial pressures of inert gasses at the surface , such as nitrogen, are now at depth, which increases nitrogen’s partial pressure within the air space in his lungs.. At depth this high partial pressure of N within the airspace within his lungs diffuses from the air in the lungs into the blood stream. At 30M (which is four times the pressure than at the surface) excessive nitrogen causes a narcotic effect which can impair cognitive function such as dizziness, delayed responses, and effects psychomotor function. What a performance hurdle!

However, the mammalian dive reflex is a response to water being splashed on the face and this signals the parasympathetic nervous system to slow down the heart rate so that the consumption of O2 is conserved.

So why does the parasympathetic nervous system do this?

I know from the hot cold test we did in the lab that when the arm was immersed in the hot water the blood vessels experienced vasodilation. This vasodilation caused a decrease in blood volume and subsequently lowered the blood pressure within the body. The sympathetic nervous system detected this and caused an effector to speed up the heart rate up in order to increase blood pressure to keep the circulation of blood within the body steady in order to transport O2 to the tissues.



(comprehensivephysiology.com)

In exercise muscle contraction creates heat. In order to maintain a stable internal temperature the body redirects blood flow to the outer extremities to be cooled. The arteries expand therefore increasing blood flow and thus decreasing blood pressure.

In contrast, West reports at a 30M depth the lung starts to collapse. The blood vessels supplying the lungs swell (dilate) as the external pressure pushes the blood from the extremities blood to the core to feed the heart and brain. These physiological experiences of pressure creates tension, constricting the blood vessels (a type of environmentally forced vasoconstriction). This in turn raises his blood pressure and in order to compensate for this, a baroreceptor detects this increased pressure and signals the parasympathetic nervous system to slow the heart rate.

So how does one adapt to this tough environment I ask? Trubridges main strategy is to be able to inhale as much air as he can and move very slowly underwater to limit the consumption of O2 by the muscles therefore limiting the production of CO2. He trains by doing lung stretching exercises to stretch the intercostal muscles and his diaphragm so it can create more volume in his thorax (where the lungs reside) so that there is an increased lower pressure in this cavity to cause an increased volume of air to be inhaled. This is where air will always move from a high pressure to a low pressure. The higher the difference the more air he can move into his lungs.

This is where increased pulmonary capacity affects performance. Trubridge trains his intercostal muscles to increase the pressure gradient between the atmosphere and the cavity inside his lungs in order to increase his total lung capacity. This training has enabled Trubridge to improve the area variable in Ficks law of diffusion to enhance his total lung capacity for better performance.

So what do I not understand? Well the article didn’t go in to depth with other possibilities of adaptation Trubridge had also developed. It can’t be all muscular adaptation within the mechanics of breathing. When comparing the adaptations of altitude training where this can increase haemoglobin capacity, it is not likely that a Trubridge would utilise this method to increase O2 carrying capacity as he lives in long island in the Bahamas and this type of training would be impractical.

Respiration and VO2 max

I know that cardio respiratory tests indicate fitness levels through measuring or  estimating your VO2max. And it was quiet interesting when you see a  VO2max  test in action. You could see that when the workload increased so did respiration and heart rate in a linear fashion. What I found interesting was when the work load increased to a point there was a change in gradient which became much steeper. This was explained to me as a ventilatory threshold.

I know that  VO2max  is the maximum uptake of O2 by the body and this is normally tested in a submaximal test where the data is been extrapolated In order to predict  VO2max . So why does the heart rate and breathing rate suddenly change gradient when the workload is increased over a certain point and why is this relevant to say playing sport?

I also know that if the aerobic system is at capacity and the work load increases again the body can utilise the anerobic system using the muscle glycogen to perform contractions to compensate for any shortfall. But in nutrition I learned that anaerobic energy systems are only used for short bursts of work. So why does the heart and breathing rate increase when the body is pushed almost beyond its “aerobic threshold”… this might be the way the body tries to buffer between competing energy systems …. Hmm

I also now know that a product of muscle contraction is CO₂. Excess CO₂ raises the PH level in the blood, As our breathing is driven by the need to remove this CO₂ from the blood to maintain a stable PH, I can understand why our breathing rate increases as the workload is increased – it needs to get rid of more CO2 as the work increases to maintain a stable PH in the blood however it doesn’t explain why all of a sudden heart rate and breathing rate sharply increases, as it’s been established that as the body does more work the higher breathing and heart rate increase and this is in a straight line.

So what?

There must be other factors at work here, things that aren’t observable. I think I will have a look at what are the responses to elevated PH levels in the blood as this may have a bearing on how the lungs and heart try to compensate for workloads over this aerobic threshold.

Also wonder if this has implications and therefore training considerations for sports that utilise both the aerobic system and the anaerobic system? Can you increase this threshold or is this a individual static value that can’t be modified like height?

So what next?

I don’t understand how adaptations are made by increasing cardiovascular and respiratory capacity happen.

Lactate threshold and ventilatory threshold

The Lactate Threshold

I read an article on the peak performance website that explains how increased lactate threshold will improve peak performance (Anderson,n.d)

I learned that Glycolysis is the production of energy from glucose. Glucose is broken down into Pyruvic acid. Pyruvic acid is then used in the krebs cycle to creates over 90% of the energy you need to run. During strenuous exercise there can be  a large accumulation of Pyruvic acid within the muscle cells.

Ok so what?

Well this large accumulation of Pyruvic acid  (pyruvate) makes a change in the normal steady state a body can function in. An enzyme (an effector) is then activated that breaks down and converts this Pyruvic acid into lactic acid (lactate).

I’ve always heard that the burning in your muscles is what they call the lactic acid build up.

Apparently not!

Lactic acid (lactate) is used to metabolise carbohydrate (CHO). When CHO is metabolised one of it's by products is Carbon dioxide and water.

Lactate is also used by the muscle to create glycogen which provides energy we store for later (wow didn’t know that). The lactate shuttle explains how pyruvate is converted to lactic acid, Lactic acid then escapes (no blocking the production of Pyruvate from Glucose) into other muscle cells where it has two uses. Firstly, it can be broken down to form ATP, or it can be used as a building block to form glycogen to be stored.

The article explains when you first start exercising your lactate levels rise as the demand for more energy is increasing. When you start exercising initially your breathing and heart rate is low which is not supplying enough oxygen. Oxygen is used to break down Pyruvate. So while yo are getting warmed up there will be a build-up of lactate in your muscles.

As your breathing rate and heart rate increase, more oxygen is delivered and more lactate is converted to energy and that’s why after some time exercising that second wind comes into effect.

However if you were to increase the amount of work within a training session to a certain point this would produce an imbalance between the lactate production (through conversion of Pyruvate) and the muscles ability to convert (or clear) the lactate from the blood. This is most likely because the muscles cannot convert all the lactate being formed so this excess builds up in the blood stream. This is called Lactic acidosis…which causes a drop in the PH of the blood which makes it more acidic-  I bet that signals an integrating centre somewhere to effect a change!

So how do we increase this lactate threshold?

Andrews states that intense training is the best LT booster, because activities that are closer to maximal capacity improves the heart's capacity to deliver oxygen, the muscles' ability to use oxygen once it's delivered, as well as the ability of the heart and muscles to 'clear' lactate from the blood.

Keith, Jacobs and McLellan (1992) did several tests involving runners training below LT, at LT and above LT. The results showed that training at LT and above provided the greatest gains however the group that trained above LT could maintain the  same amount of work for longer – This result shows quite clearly the application to increase adaptation for endurance sports

From this information, In order to increase my football boys overall aerobic capacity and increase their lactate thresholds I will be adding some intense interval training activities (15min each) within training sessions as not only does adaptation occur when one works above the lactate threshold as opposed to below it but short bursts working at these levels provides the same adaptation rates as longer durations at the lactate threshold or below.

What do I need to understand more about?

What happens when the PH of the blood drops in the blood stream and what are the responses?? 

 

 The Ventilatory Threshold

A test we completed was a graded exercise test where a participant on a tread mill was exposed to increasing loads whilst measuring heart rate and breathing rate through specialised equipment. There is a principle that during a submaximal test, heart rate and breathing rate increase in a linear fashion as work increases. So the more distance a runner runs and the faster they run the more work they are doing (Work + force x distance. This was evident for most of the test until a certain point where the gradient sharply increased. So what?

McArdle et al. (2010) explain this phenomenon as reaching a “ventilatory threshold”. They state that that ventilatory threshold is the point in which ventilation increases disproportionally with O₂ consumption. With sub maximal tests a straight line occurs. However the change in respiratory frequency could indicate a maximal level of exercise has been reached.

So what do I not understand?

Why does ventilation increase disproportionately with O₂ consumption?

When we did some submaximal and maximal tests in a lab to measure VO_2max. I know that cardio respiratory tests indicate fitness levels through measuring or estimating your VO_2max. And it was quiet interesting when you see a VO_2max test in action. You could see that when the workload increased so did respiration and heart rate in a linear fashion. Fick’s Equation explains that VO_2max is equal to cardiac output (Q) multiplied by the difference in the arterial (ā) and venous (ṽ) O₂ content of the blood.

VO_2max = Q x (ā - ṽ diff).

So what is cardiac output?

Cardiac output is how much blood your heart can pump in a minute and is described as the stoke volume (that’s how much volume of blood your ventricles can pump per contraction) multiplied by how many contractions within that minute. I would relate this to being similar how much gas a petrol pump could pump out in one minute.

What I found interesting was when the work load increased to a certain point there was a change in the breathing rate gradient which became much steeper. I know that VO2 max is the maximum uptake of O₂ by the body and this is normally tested in a submaximal test where the data is been extrapolated In order to predict VO_2max. At certain point in the graded exercise test (where work was increased in incriments over time) breathing rate showed a sharp increase in gradient and no longer travelled in a linear fashion even when the increased workload stayed the same.

So why does breathing rate suddenly change gradient when the workload is increased over a certain point?

This was explained to me as a ventilatory threshold (V_T). OK so what is that exactly?

McArdle, Katch and Katch (2010) explain in chapter 14 that ventilatory threshold “describes the point where pulmonary ventilation increases disproportionately with O₂ consumption”.  Apparently this means that the breathing rate is no longer tied to the amount of O₂ our muscles demand but the build-up of CO₂ within the blood stream through the glycolysis process (anaerobic process). Ok so I understand that breathing is in fact driven by CO₂ removal. 

So how is this CO₂ produced?

Glycolysis is a process whereby energy is created using glucose in the blood. This glycolysis process creates lactate. As we exercise and increase our work rate, more lactate is produced. The body’s homeostatic receptor mechanisms detect this change in PH within the blood. This causes a buffer to be produced which is called sodium bicarbonate (this is homeostatic effector mechanism!). This reaction between lactate and sodium bicarbonate causes CO₂ and water (H₂O) to be produced. Normally the rate of lactate removal is equal to the rate it is being produced even at high concentrations of lactate production. When work load increases Our Heart rate increases to deliver more blood to the lungs in order to remove the waste (CO₂). If this build-up of CO₂ is beyond our capacity to remove it through our lungs, the response is to increase breathing rates. If by doing this the PH is still within unacceptable limits our breathing rate will increase further. This is why our lungs are the limiting factor on our performance! In application, looking after your lungs would be paramount for any athlete.

This is the main reason why promoting being “smoke free” to our athletes is so important. If we reduce our capacity to remove CO₂ we reduce our ability to perform.

So if I were to explain this to students:

As we perform more work our heart rate and breathing rate increase in a straight line. When work increases to a point where our breathing rate increases disproportionately this is the “ventilatory threshold”.

The lactic threshold is caused by a build up of carbon dioxide fromin the blood due to not enough oxygen being supplied to break this Lactate down to energy. This causes a drop in PH within the blood. This increased acidity drives the needs to expel more CO2

As the work rate of our muscles increases, the CO2 produced by the muscles increases also. This increased CO₂ within our blood makes the blood more acidic (lower PH). Detection of increased acid in the blood causes the heart to beat faster. This delivers more blood to the lungs to expel this waste in order reduce the acid levels in the blood.

At this point the heart is delivering blood at a rate that matches the work. Fick’s Law of diffusion states the rate of gas exchange across tissues is dependant on tissue area, membrane thickness, gas co-efficiency and the difference in partial pressure of the gas between the blood and the atmosphere. If our lungs can’t diffuse enough CO2 across the alveolar membrane per expiration, the response is to increase the breathing rate.

You will feel as if this is a desire for more air – gasping for breath when you have done a really intense run.

Thermoregulation

Thermoregulation has been one of the things I have needed to understand within boxing, diving and other field sports I have participated in. I’ve also had hydration issues in the past. By understanding what causes imbalances that affect homeostasis can enable me to better manage and maintain a stable state when playing sport or exercising.

Heat or the inability to lose heat fast enough is something I find limits my performance and can cause me serious medical issues when boxing. For example, after a rather strenuous session I started feeling my heart pounding, I couldn’t think straight and I felt drained of energy. From observation, my face goes bright red and my clothes are saturated with sweat. Heat was a major issue

I found the process of thermoregulation really interesting as I frequently experienced a wall when I just had nothing else to give. I used to think it was just because I had run out of energy that I was not able to continue when in fact it probably was a combination of dehydration and exhausting energy supplies because as soon as I rested and rehydrated I would be able to get up and be able to perform. It was my body’s way of saying to me “stop as I can’t cope with this level of activity anymore ”

When I did my Dive Masters course I also learned that water conducts heat over 20 times faster than air. This is why sweating is most efficient response to the regulation of increased temperature of the body. In diving reducing the amount of water that touches the skin results in less heat lost and therefore a wetsuit limits the amount of water coming into contact with your skin and helps to keep you warm, whereas when exercising the sweat is designed to increase the amount of heat losses in order to stop the body from overheating.

So how does all this work? How am I going to supply this information to my students so they can relate and therefore understand?

I watched this You Tube video about thermoregulation (because I’m a visual and kinetic learner) which helped to explain how the body regulates its temperature during exercise.

http://www.youtube.com/watch?v=zcdGJDGXxgs&list=PLCE5C2E8388C06BF9&index=3&feature=plpp_video

Even though the environment around us is continually changing, our bodies need to maintain a constant internal environment if they’re to work properly. This process of regulation maintains “homeostasis” at rest or a “steady state” during exercise. The human body is able to maintain this stable internal environment through negative feedback systems.

This means that there are complex systems and processes that happen within the body to maintain acceptable levels to maintain life. How this works is that within the body a “receptor” detects a change in the internal environment, it then reports the change to a “integrating centre” that decides on whether this change requires action and then directs an “effector” to make the change to correct the internal environment. So how does this apply to sport and exercise?

Firstly the body needs to keep a relatively stable temperature between 36.ºC and 37.8ºC to maintain life. The process in which the body tries to keep a stable internal temperature such as in hot or cold environments is called “thermoregulation”. This involves specific feedback systems that report to the Hypothalamus (the bodies thermostat) which integrates (this feedback and instigates an effector to correct the internal environments temperature. This effect can be observed as sweating.

So how does sweat regulate temperature?

Thermoregulation is the balance between heat input and heat output. There are two sources of heat production. Firstly, internal heat production is done through metabolic processes (eating food) and by muscle contraction (doing exercise, moving around) which accounts for most heat production in the body. Secondly, external heat production is supplied from the environment around us such as a heater, hot water, the sun on a hot day or competing under hot lights.

There are four ways heat can be lost and gained by the human body. These are “conduction”, “convection”, “radiation” and “evaporation”. The most relevant to exercise is convection and evaporation. These mechanisms for transfer of heat play a major role in thermoregulation.

So what do these terms mean?

At rest, in a cool or hot external environment, heat can be released or absorbed via a process called radiation. Within exercise, “convection” describes moving heat from the surface of the skin to the gas that is in the air for example when a breeze can cool you down after a run.

Evaporation involves a liquid turning into a gas by way of heat – in science class in order to turn water into a gas you needed to apply heat. Another more domestic example is if you ever remember taking a hot pan off the element to wash it and filling it with a small amount of cool water, the water evaporated into steam and the pan lost its heat. Although less dramatic, sweat is produced to so we can use the liquid via evaporation to remove heat from the body.

In environments that are hot, the body’s ability to regulate temperature becomes more difficult as the body becomes more dependent on the evaporation of sweat to remove heat from the body as radiation, convection and conduction become less effective as the temperature of the environment increases (Wilmore, Costil & Kenny. 2008).

So how is sweat created?

There are thermo receptors located both on the skins surface to detect changes of temperature of the external environment and within the hypothalamus that detect changes in temperature in the internal environment. The hypothalamus is also the control-centre for temperature control within the body. When an unacceptable rise of internal temperature is detected by the hypothalamus thermo receptors it sends out impulses that stimulate the sweat glands on the skins surface. This process of cooling down starts with the blood vessels expanding to supply more blood to the skins surface which is called “Vasoldialation”. If this does not reduce the temperature of the internal environment the sweat glands are stimulated to produce sweat which evaporates on the skins surface removing the heat from the internal environment.

In cold environments, such as when diving, the hypothalamus send signals to the body to create more heat.
The body constricts it’s blood vessels to prevent further heat losses and since muscle contraction is the primary source of heat generation, shivering occurs or fat mass is burned to create heat.

The source of sweat comes from the water content of plasma (Wilmore, et al., 2008). Sweat also contains small amounts of electrolytes during light sweating however with increased or excessive sweating electrolyte concentration increases. If excessive sweating for long periods of time, such as in vigorous exercise like running can deplete the body of water and electrolytes. This causes blood to lose its water content and therefore become thicker. This makes it hard for the heart to pump blood around the body.

This can cause issues for performance as the body can experience; cramps, which is the body’s inability to provide blood to the muscles; Heat exhaustion, when the body’s demands from the muscles and skin outweigh what the body can supply; and heatstroke, which is life threatening, where the body’s thermo regulatory systems completely fail.

So what?




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Maughan, R. J., & Shirreffs, S. M. (2010). Development of hydration strategies to optimize performance for athletes in high-intensity sports and in sports with repeated intense efforts. Scandinavian Journal Of Medicine & Science In Sports, 2059-69.

This article made me think about what I could do to combat heat stress in sport or advise my students about proper hydration prior, during and post exercise.

The articles stated that when single performance strength and power activities such as sprinting were not affected when hypohydrated (less than optimal hydration). In fact in some cases the less blood volume meant less body mass to move. In the case of sprinters or long jumpers this actually helped their performance as there was more power to weight ratio.

However, in endurance events or intermittent short term high intensity performance such as long distance running or soccer, performance was affected negatively due to hypohydration. Affects such as decreased mental and physical function can occur. This makes hydration extremely important when complex tasks such as sprinting, endurance and skill are required.

The type of sport also determines the opportunities for hydration during the performance. Soccer players are on the field for 90 minutes with only one opportunity to hydrate during half time. Endurance runners have to run while they drink and must drink small amounts frequently. American football has many stoppages where opportunities to hydrate are available. The duration of exercise also plays a significant partTherefore hydration strategies must consider demands and opportunity for hydration.

Another consideration is the environment. There is also a large variability in people’s sensitivity to dehydration and therefore performance. An endurance runner or cyclist could run a variety of different places that vary in temperature. It was shown that a 2+% loss in body mass due to hypohydration can impair endurance performance between 7% and 60%. Therefore Hydration strategies need to be individualised not only to the type of environment the event takes place in but also how the individual responds to hypohydration and how this effects their performance. For instance, an endurance runner must time their intakes during the race to reduce “hitting the wall” and their individual thresholds need to be examined as part of their preparation for events.

The Paula Newby video(http://www.youtube.com/watch?v=g_utqeQALVE) demonstrated that a miscalculation of her hydration led to a shut-down of the body’s ability to perform resulting in the inability to co-ordinate her muscles (ataxia), reduced cognitive function and her body’s ability to regulate temperature.

At the opposite end, Hyperhydration can lead to increases in body mass and therefor increase the work rate

As educational and secondary school sports events are not held at an elite level and critical effects may not occur it is still wise to ensure amounts adequate hydration and opportunities to hydrate are well managed. My advice after reading this article is to impress upon students the importance of hydration pre, during and post event using this evidence as a teaching point. During training and practices ensuring the availability of water can reduce muscle cramps and maintain performance. Stressing that players should hydrate prior to performance, drink when they feel thirsty is one way however ensuring they also drink enough post match is equally important. Making it mandatory that players must bring a drink bottle to training can maximize their opportunities to hydrate and get them into the practice of self-regulating their hydration.

Fast fact

The sensation of thirst is a detection in loss of blood volume due to dehydration. A we dehydrate, the brain detects a increase in blood thickness. The heart detects a decrease in blood volume. These receptors alert you and the sensation is felt as thirst.

Homeostasis

Homeostasis is the integration of body systems that is able to maintain a constant unchanging internal environment. Typically homeostasis is what we experience at rest. Exercise places stress on the body which disturbs homeostasis. When exercising the body has mechanisms that can maintain a “steady state” which help to maintain a safe internal environment. All homeostatic mechanisms use negative feedback to maintain a constant unchanging environment to maintain a set-point which the body considers normal.

In order to maintain a safe internal environment, the body has self-regulating control systems. These control systems are made up of receptors, an integrating centre and an effector that corrects any undesirable imbalances within the body to return it to this set-point.

The effector detects a stimulus or change within the body’s system. These then send signals (negative feedback) to the integrating centre. The integrating centre interprets this signal and compares this to the set-point and sends a stimulus to an effector. The effector corrects these changes in order to maintain homeostasis. If a change is made and the receptors still detect an imbalance the cycle will repeat itself until a stable state (acceptable) is achieved. For example when you exercise you sweat. This is an example of how control systems at work within exercise:

There are two sets of thermoreceptors: receptors in the hypothalamus which monitors the temperature of the blood as it passes through the brain (core temperature) and receptors on the skin which detect the external temperature. (McArdle, Katch and Katch, 2010)

The hypothalamus itself is also the integrating centre which compares the detected temperature with the desired temperature. If this detected temperature is outside the safe bandwidth of acceptable body temperature (37_o ±0.5^o) it sends a signal to an effector to correct the change. The bigger the change detected the bigger the response.

So what? Where can I see Homeostasis in action?

During a boxing training session I can feel my heart rate increasing, my breathing becomes deeper and more frequent, my skin becomes flushed, I sweat and my muscles start to become fatigued. At the end of a training session I’m thirsty and thoroughly tired.

These symptoms or otherwise known as responses to exercise are examples of systems at work to maintain this “steady state” during exercise in order to function effectively for performance.

So what are these systems?

The cardiovascular system is working harder to supply the tissues with more blood which contain oxygen (O2). Breathing rate is increased to possibly keep up with increased demand. I’m red in the face because I’m hot and by sweating I am trying to cool down my body temperature. I’m drained of energy because I know from nutrition studies the muscles have limited stores of glycogen that supply Adenosine triphosphate (ATP) in order to contract my muscles.

I also have observed different responses when training on a cold day or a hot day. On a cold day I shiver before training until I get warmed up. On a hot day I sweat more than on a cold day. In a humid day I feel almost suffocated as I am unable to cool down just by sweating – I normally need to pour cold water on my face and the back of my neck. My body is trying it’s hardest to maintain a stable internal temperature.

McArdle, Katch and Katch (2010) explain the stable temperature of a human body is approximately between 36-38o. In a cold environment we experience heat loss. Most people shiver to keep warm. In a hot environment most people become too hot and tend to sweat.

When thinking about my training routine, why do I have to warm up just so I can get hot and start sweating only to have to warm down?

I learned in exercise prescription that a warm up and warm down is essential as this helps the body prepare for exercise and help it get back to a resting state. I was always told that warming down prevented the likelihood of getting a chill and possibly the flu. I could assume now that warming down could be the gradual internal return to homeostasis from a steady state during exercise. I have always warmed up the football team I coach and explained that we do this to get ready for more intense drills during practice and so we are ready for game performance. I get them to warm down in order to reduce muscle soreness and avoid chills. So what else ?

Obviously many systems change in order to for us to perform exercise. So what happens to our cardiovascular, respiratory and cooling systems when we perform more work such as exercise and performance in sport?

Other areas I think I can see homeostasis at work is within nutrition. When trying to gain or lose weight the body has a set point in which it tries to maintain its current weight. The body doesn’t like change and if we try to adjust our intakes it tries to correct any nutritional imbalances or changes to diet by either increasing appetite or storing excess caloric intakes as fat. This is why we must gradually reduce or increase caloric intake to get the desired result.

From exercise prescription I know you need to apply the principle of overload to make adaptations. I know that in order to get fitter or improve performance you must do more work. If you do more work you increase the disturbance to homeostasis.

What do I not understand?

How is sweat created and why?

How do other systems work together to maintain a steady state when exercising?

So if you want to get fitter or improve your performance how do these systems adapt to an increase in work and how does this increase performance? What modes cause what adaptations?

Oxygen from the Atmosphere to the Blood

The mechanical structure of the respiratory system is made up of a conducting zone and a respiratory zone. The conducting zone warms and humidifies the air we breathe in order for gas exchange within the respiratory zone where gasses are diffused from the atmosphere to the blood and vice versa.

The air is made up of Nitrogen (79%) and Oxegen (20.9%). Gas transfer between the external environment (outside the body) and the internal environment (the bloodstream) is governed by two things, the partial pressure of a gas in the atmosphere and the partial pressure of a gas within the blood stream. Gasses with higher partial pressures will always flow to a place where the same gas has a lower partial pressure. The difference between the pressure of a gas in the atmosphere and the blood will dictate which direction the gas will travel. For example, If the blood stream contains a lower partial pressure of Oxygen and a higher partial pressure of carbon dioxide (CO₂) than in the atmosphere, the oxygen from the atmosphere will diffuse through the lungs into the blood stream and the CO2 will transfer into the atmosphere. This transfer of gasses is why we breathe.

An example as we dive to depth the Pressure increases due to the increased weight of all that water and gravity. Therefore partial pressure of O2 and Nitrogen increases. Our bodies have a lower partial pressure of these gasses within it. Therefore we absorb more O2 and Nitrogen into our blood stream. During ascent the inverse happens. 

One way to explain this pressure gradient concept is to imagine a long sausage-like balloon. Pinching it loosely in the middle would symbolise the membrane in which gass transfer happens. Now squeeze one end. The increased pressure put on the squeezed end would force the air to move to the other end so that it would inflate more. If you let go of the squeezed end the air would move back to the end that had experienced lower pressure.

So what rates does gas diffuse from the atmosphere into the bloodstream?

This does depend on a few things. Ficks Law of diffusion states that a gas diffuses through a sheet of tissue at a rate directly proportional to the tissue area (A), diffusion co-efficient of gas (D), and the difference between the partial pressures of each gas on each side of this tissue (P₁ – P₂) and is inversely proportional to the tissue thickness (McArdle, Katch and Katch, 2010).

In exercise and physical performance we want this diffusion to be as efficient as possible. For aerobic sports that rely heavily on being able to utilise O2 such as swimming, running, cycling and other sports that involve the aerobic system, this would be really important. For example, if an asthmatic has a large build up of mucus over the inside of the lungs,This increases the tissue thickness (membrane) and decreases the area of the lungs. Therefore when applying Ficks law of diffusion you could say that a thickened membrane will reduce the diffusion of O2 into the blood stream and therefore the supply to the muscles that use this O2 would be limited, therefore reducing performance of those muscles.

So we would have to assume that O2 drives breathing?
Short answer... no CO2 does


Why?
A by-product of muscle contraction is CO2. CO2 when it gets into the blood stream it binds with water (another by product of muscle contraction). This lowers the PH level of the blood. This in turn makes the blood become acidic. As we exercise more CO2 is released into the Blood stream. Aha! you say but doesn't the tissues demand O2 also?

Although the body needs oxygen for energy metabolism, low oxygen levels normally do not stimulate breathing.


(http://www.therelationshipseries.com)

Take for example the article 100M Man - William Trubridge (Scott, 2007). Trubridge is a breath hold diver who can hold his breath for over 8 minutes. There are many things that a breath hold diver must overcome to be able to perform breath hold for long periods.

Firstly he has to overcome the desire to breathe. This urge is caused by a build up of CO2 within the blood stream. This CO2 is produced by his tissues. Increased CO2 within the blood causes the blood to become more acidic. The urge to breath is a rise is acid within the lungs tissues. This is called respiratory acidosis. Molecules of CO2 is produced faster than O2 is consumed. CO2 builds up in the bloodstream faster than O2 is consumed. This builds up acid and triggers the response to breathe.


So how is O2 used - what happens once it gets into the blood stream?

Oxegen Content of the blood

What transports oxygen to the tissues?

Oxygen (O2)as we know is diffused through the lungs into the bloodstream. The oxygen carrying component within blood is in the red blood cell and is called haemoglobin. Haemoglobin carries four heme (iron) molecules which oxygen binds to when they diffuse across the Lungs alveolar membrane into the blood.

So how does oxygen get off the haemoglobin?

When the CO2 concentration gets to a certain level within the blood, this signals the heme to release the oxygen molecule. This is then diffused through the cells membrane and is consumed by the cell. If the CO2 levels in the blood get higher the heme releases its second molecule and so forth. This is called the Bohr effect

The Bohr effect: The dissociation curve for Oxy-haemoglobin is shifted to the right with increasing carbon dioxide or proton concentration in blood.

So how can i see this effect in exercise or sport?

“100m Man” William Trubridge (Scott, 2007)

This article is about a Breath hold diver that has been able to dive on a single breath for over 8 minutes!

But you say how did he do that? how did he not run out of oxygen?