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Acclimatisation To Altitude and Heat

Ben and Tala:

Assess why an athlete might prepare for an event in the Olympics with altitude training.

Omar, Jamie, Rama:

Describe the responses to the CV system when at altitude.

Performance in Heat / Humidity

Heat illness is an inherent risk when exercising in hot conditions and can affect even the best-conditioned athlete.

Not identifying signs/symptoms of heat illness can result in severe dehydration and, in extreme conditions, death.

Exercise-associated muscle (heat) cramps are painful, involuntary muscle contractions most often caused by dehydration, electrolyte imbalance and fatigue.

Light-headedness is usually seen at the end of a race or after an individual stands for a long period of time after completing a physical activity. The possible weakness, dizziness and fainting experienced can be attributed to pooling of blood in the extremities.

Performance in Heat / Humidity

Exercise (heat) exhaustion should be suspected in an athlete whose performance rapidly declines and who lacks the ability to continue exercising.

The athlete may experience extreme thirst; dizziness; headache; profuse sweating; weak and rapid pulse; and gray, cool, clammy skin.

Athletes especially at risk for developing a heat illness are individuals who are overweight, dehydrated, under-conditioned or very muscular. Those who practice during the hottest times of the day and who are not acclimated to the environment, have to wear protective equipment (helmet, shoulder pads) or have a history of heat illness are also at elevated risk.

Preparing for Competition at Altitude

One approach is to compete within 24 hours of arrival at altitude. Not much acclimatization will have taken place but most of the classical symptoms of altitude sickness will not have had time to manifest.

An alternative option is to train at a higher altitude for at least 2 weeks prior to competition. Although full acclimatization to altitude takes 4 to 6 weeks, many of the physiological adaptations occur in the first 2 weeks and the more severe disturbances should have settled. It is important to remember that during the initial days at altitude work capacity is reduced, so athletes should train at 60-70% of sea level VO2 max and build up gradually over 10-14 days.

A third approach is to devote a greater percentage of training time at sea level to endurance training several weeks prior to competition. This is a strategy often adopted within many team sports, helping to raise players' VO2 max to a peak so that they can perform at a lower relative intensity without significant loss in performance.

Performance in Heat / Humidity

Cardiovascular System Response to Altitude

Heat acclimatization or practicing in the environment the athlete will be playing in will allow the body to adapt to the warm environment, which will improve performance and heat tolerance.

Athletes should progressively increase the intensity and duration of their training sessions over a 10-14 day period to become fully acclimated to their environment.

An individual properly acclimatised should be able to train in the warm environment for one to two hours at an intensity equal to competition.

Blood volume decreases. Plasma volume decreases by up to 25% within the first few hours of exposure to altitude and doesn't plateau until after a few weeks. This is partially a deliberate response by the body as reducing plasma in effect increases the density of red blood cells. While no extra red blood cells have been produced in this acute phase, the amount of hemoglobin per unit of blood is now increased resulting in greater oxygen transport for a given cardiac output

Cardiac output increases during rest submaximal exercise. During the first few hours at altitude stoke volume decreases during submaximal exercise, a result of the reduction in plasma volume. Heart rate increases enough to compensate for this and therefore slightly raises cardiac output. After a few days however, oxygen extraction becomes more efficient reducing the need to increase cardiac output.

Maximal cardiac output decreases. During exhaustive exercise at maximum levels both maximal stroke volume and maximal heart rate decrease with altitude. This obviously combines to have a significant effect on maximal cardiac output.

Respiratory System Response to Altitude

Breathing rate increases at rest and during exercise. A smaller number of oxygen molecules per given amount of air means that increased ventilation is required to consume the same amount of oxygen as at sea level.

Oxygen diffusion decreases. At sea level oxygen exchange from the lungs to the blood is unhindered and the oxygen-carrying component of blood, hemoglobin, is about 98% saturated with oxygen. As altitude increases and the partial pressure of oxygen in the air drops, so does the pressure gradient between oxygen in the lungs and blood.

The diffusion gradient at the active tissues decreases. As mentioned above, oxygen passes from the lungs to the blood due to a pressure gradient. The same process occurs when oxygen-rich arterial blood reaches the active tissues. At altitude arterial oxygen pressure decreases so the difference or pressure gradient drops. In effect, less oxygen passes (diffuses) from the blood to the tissues

VO2 max decreases. Maximal oxygen uptake begins to decrease significantly above an altitude.

Performance in Heat / Humidity

Choosing clothing and equipment that is light-colored and loose-fitting will help keep an athlete cool.

As the temperature increases, athletes should minimize the amount of clothing and equipment (helmet, shoulder pads) worn.

The body’s ability to cool itself through the evaporation of sweat decreases significantly as the amount of equipment worn increases.

Athletes who must wear protective equipment should allow time to start training in shorts and T-shirt and gradually add equipment each day as their bodies acclimatise.

It makes sense then that any reduction in the pressure of oxygen entering the lungs will reduce the pressure difference or gradient.

The result is less oxygen being driven from the lungs into the blood.

At altitude that is exactly what happens

Up to 1500m (4921ft), altitude has little effect on the body.

Above this level, studies show the cardiovascular, respiratory and metabolic systems are affected.

Recap

After we inhale, oxygen in the alveoli (tiny air sacs in the lungs) passes to the blood to be transported to the tissues.

This gas exchange between the alveoli and blood takes place due to a pressure difference called a pressure gradient.

The pressure oxygen exerts in the alveoli is greater than the pressure of oxygen in the blood surrounding the lungs.

This drives oxygen from the lungs into the blood.

High Altitude Environment

the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own.

What is partial pressure?

Air at altitude is commonly mistaken for being lower in oxygen but this is incorrect.

As elevation increases, oxygen has a progressively lower partial pressure

At sea level, air exerts a pressure of approximately 760mmHg. At the summit of Mount Everest, 8848m (29,028ft) above sea level, air only exerts a pressure of about 231mmHg

Explain the process of inhalation

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