Short term Acclimatisation - Environmental factors

Short term Acclimatisation - Environmental factors

1. The Environment can have a huge effect on Performance. Factors such as temperature (cold as well as heat), humidity, altitude, pollution, prevailing winds and the playing surface are all taken into account before competition.

   • HEAT ACCLIMATISATION In hot climates, the problem is not maintaining body heat, but dissipating it.
   • In cold climates, the athlete needs to consider the extra clothing required, and the consequent weight and drag effects of the clothing. From a physiological perspective, extra clothing will generally lead to additional sweating, which needs to be met with additional hydration strategies.

2. VO2 max (maximal oxygen consumption, maximal oxygen uptake or aerobic capacity

3. PHYSIOLOGICAL RESPONSES TO HEAT The early adaptations to heat (during the initial one to five days) involve • expanded plasma volume (see page 25) • improved control of cardiovascular function • reduced heart rate • autonomic nervous system habituation (this involves the more long-term redirection of cardiac output to skin capillary beds and active muscles that might be expected during some extreme endurance events).

   • Key terms hypothermia a condition in which the body temperature drops below that required for normal metabolism and bodily functions hyperthermia an acute condition that occurs when the body produces or absorbs more heat than it can dissipate (sometimes referred to as heat stroke or sunstroke)

4. GETTING IT WRONG - HEAT ILLNESS The most common heat illnesses among athletes are heat cramps, heat syncope (fainting) and heat exhaustion.

   • HEAT CRAMPS Cramps usually occur in the muscles of the legs, arms and abdomen after several hours of strenuous exercise, in individuals who have lost a large volume of sweat
     • Sodium depletion probably causes heat cramps.
   • HEAT SYNCOPE Heat syncope or fainting occurs most commonly during the first three to five days of heat exposure. This is due to the vascular shunting of blood to the skin in order to cool down, and the consequent reduction in venous return and subsequent drop in cardiac output, in turn leading to a drop in blood pressure.
   • HEAT EXHAUSTION This is the most commonly diagnosed form of heat illness among athletes, despite the fact that its symptoms are often vague, and differ greatly from one situation to another. Clinical descriptions include various combinations of headache, dizziness, fatigue, hyperirritability, tachycardia, hyperventilation, diarrhoea, hypotension, nausea, vomiting, syncope, heat cramps and ‘heat sensations’ in the head and upper torso

5. HYDRATION PLANNING Attention to hydration, and awareness of the potentially damaging effects of dehydration, are especially important in hot conditions. Hydration planning is a vital element of acclimatisation

6. EFFECTS OF ALTITUDE Aerobic performance at altitude is more difficult, so rates of performance decline when compared with those attainable at sea level. At higher altitude, the partial pressure of oxygen (ppO2) is reduced. This leads to a reduction in the driving pressure for oxygen transport, and a corresponding fall in VO2 max of around 5–7 per cent per 1000 metres.

7. Key term - Erythropoietin a glycoprotein hormone that controls production of red blood cells

8. Key terms hypoxia a shortage of oxygen in the body hypoxemia a deficiency in the concentration of dissolved oxygen in arterial blood. Hypoxemia is different from hypoxia, which is an abnormally low oxygen availability to the body or an individual tissue or organ. The type of hypoxia that is caused by hypoxemia is referred to as hypoxemic hypoxia.

   • HYPERVENTILATION The hyperventilation (or increased pulmonary ventilation) response is immediate on arrival at altitude. It is more pronounced during the first few days, and then stabilises after about a week.

9. OTHER RESPONSES • Elimination of bicarbonate (HCO3 –) in the urine – its main function is to maintain blood pH at near-normal levels. • Increased muscle and tissue capillarisation – the growth of more capillaries within the muscles enables more blood to be delivered into the muscle. • Increased myoglobin concentration – this enables the tissue to extract more oxygen from the blood, and also to remove more CO2. • Increased mitochondrial density – this enables greater and faster production of ATP through aerobic respiration. • Enzyme changes that enhance the oxidative capacity – greater quantities and more availability of the enzymes used during respiration.