Short-Term Acclimatisation

Environmental factors, heat adaptation, hydration planning, increase plasma volume, increase sweat rate and effects of altitude.



Competiions or matches in unsusual conditions require time to get used to the conditions. Acclimatisation is the process of the body etting used to these conditions. Different environmental conditions cause the body to adapt. 

Time length for acclimatisations takes place in either a few days to weeks. Adaptations made by the body are usually reversable so the adaptations are short-term responses. 

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High Temperatures

Responses to Heat

  • expanded blood plasma volume
  • imporoved control of cardiovascular function
  • reduced heart rate
  • autonomic nervous system habituation (more long-term redirection of cardiac output to skin capillary beds and active muscles)

Regulation of Body Temperature

The thermoregulatory centre is the hypothalamus.Body temperature is maintained by balancing heat input and heat loss.

Heat Input: Metiablic Heat, Exercise, Shivering, Solar Radiation

Heat Loss: Radiation, Conduction, Convection, Evaporation

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High Temperatures

High humidity decreases the ability to sweat and therefore lose heat by evaporation during exercise in hot weather. This is due to the water content of the air being greater than normal. 

Body Size

  • Small surface area-to-body mass ratio (more fat) are more susceptable to hyperthermia
  • This is due to larger people having bigger heat production in muscle and tissue with less skin in proportion to radiate of sweat away heat energy
  • People with large amounts of subcutaneous fats (under the skin) have an insulation barrier to heat conductions from the body core, so conduction is reduced

Adaptations to Heat

  • improved cutaneous blood flow (transports metabolic heat from deep tissues)
  • effective distribution of cardiac output (circulation to skin and muscles)
  • lowered threshold for start of sweating (evapourative cooling occurs faster)
  • more effective distrubtion of sweat over skin surface (optimum use of skin surface)
  • increase sweat output 
  • lowered sweat salt concentration (to preserve electrolytes in body)
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Low Temperature Regulation

  • More heat energy is generated to raise body temperatire which is achieved by shivering - repeated muscular contractions
  • There is withdrawal of blood from peripheral body parts of the body to the core such as skin, hands and feet
  • Kidneys begin to excrete water as urinw ro reduce total fluid plasma volume held centrally. The athlete should replace fluid loss once warm up again
  • If thick clothing is worn the sweating is increasd which could lead to dehydration
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Effects of Altitude on Respiratory System

  • Breathed air is at low pressure
  • Low O2 pressure
  • Reduced O2 in haemoglobin to 94% as opposed to 98%
  • There is 4% less O2 available
  • Althletes must work even harder for the same results
  • Hypoxia (lower than normal levels of oxygen in blood/tisses)
  • Affects areobic exercise in which oxygen is needed to provide energy

Adaptations of Respiratory Systems

  • Increased manufacture of red blood cells (erythropoietin production)
  • Reduction in plasma volume
  • Effect of the two above increase the haemoglobin concentration in blood flowing to the active tissue
  • Oxygen-carrying capacity of the blood increases
  • Increase of up to 16% myoglobin content
  • increase mitochondria and oxidative enzymes to improve working capicity of muscles
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Altitude Training

Short-term symptoms to altitude training include headaches, dizzinness, increased breathing and increased heart rate. Therofore initial activity should be shorter and less intense compared with normal sea level performances.

There is minimal affect of altitude training on anaerobic activity as there is no short term demand for oxygen. Although small effect on sprinters due to reduced air pressure and therefore reduced air resistance. (e.g. 100m, 200m, 400m, long jump and triple jump at 1968 Mexico Olympics)

Altidtude training of elite endurance athletes consists of 2 visits (at least 2 weeks per visit) to altitude. The second is just prior to major competition. It stimulates production of haemoglobin and myglobin, mitochondroa and oxidative enzymes.

On return to sea level there is an increased VO2 max and tissue cell respiration, leading to enhance aerobic performance. Optimum time to complete is within 3 days of return to sea level. After this, adaptations gradually return to normal over a peroid of weeks depending on the duration spent in altitude. 

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Hypobaric (Hypoxic) Chambers or Houses

Places which use low oxygen environments to simulate altitude training. Hypobaric chambers are used by endurance athletes such as distance runners, triathletes and endurance cyclists. 

The hypoxic tent is a less expensive system where a tent is infused with low oxygen air but normal sea-level pressures. The sportsperson can sleep in a tent and gain hypoxic adaptations while asleep. 

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Getting Heat Acclimatisation Wrong

Heat Cramps: Occur in muslce sof ht legs , arms and abdomen after several hours of strenuous exercise in those who have lost large volumes of sweat and drunk large volumes of hypotonic fluid They have also excreted small amounts of urine. Na+ depletion causes heat cramps.

Heat Syncope: Fainting occurs commonly during first 3 to 5 days of heat exposure. This is sude to vascular shunting of blood to skin in order to cool down and the reduction of venous return. There;s a drop in cardiac output and therefore lowered blood pressure.

Heat Exhaustion: Most common form of heat illness amoung athletes although symptoms are vague. Includes combinations of headacges, diziness, fatigue, hyperirritability, tachycardia, hyperventilation, diarrhoea, hypotension, nausea, vomiting, syncope, heat cramps and 'heat sensations'.

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Hydration Planning

Attention to hydration and awareness of the damaging effects of dehydrations are important in hot conditions. 

During an endurance event, you should drink just enough to be sure you lose no more than 2% of pre-race weight. This can be achieved in the following way:

  • Record your naked body weight immediately before and after a number of training sessions, along with details of distance/duration, clothing and weather conditions
  • Add the amount of fluid taken during the session to the amount of weight lost - 1 kilogram (kg) is roughly equivalent to 1 litre of fluid (1lb approx. 0.5 litre)
  • After a few weeks you should begin to see some patterns emerging and can calculate your sweat rate per hour
  • Once you know what your sweat losses are likely to be in any given set of environmental conditions, you can plan your drinking strategy for any particular event
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Responses to Altitude

  • Elimination of bicarbonate in urine
  • Increased muscle and tissue capillarisation (growth of capillaries in muslces)
  • Increase mitochondia density enables faster production of ATP
  • Increase myoglobin concentration
  • More oxidative enzymes
  • Hyperventilation on first couple of days, but stabilises after a week
  • Increase number of red blood cell and haemoglobin content (rapid in first few weeks at altitude but requires 3 months for optimum level of red blood cells)
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