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.