The body acclimatizes through physiological adaptations that reduce strain and help maintain homeostasis. Heat and humidity primarily alter thermoregulation and fluid balance, while altitude causes respiratory and haematological adaptations that improve oxygen delivery.
The Reasoning and Mechanisms
Acclimatization is a gradual, reversible adaptation to a natural environmental stressor. It differs from an acute response: acute responses occur immediately, whereas acclimatization develops after repeated exposure over days or weeks.
| Environment | Main challenge | Acclimatization mechanisms |
|---|---|---|
| Heat | Increased core temperature and dehydration | Plasma volume expands; sweating begins earlier and at a lower core temperature; sweat rate increases; and sweat becomes more dilute because aldosterone promotes sodium reabsorption. Improved skin blood flow and evaporative cooling reduce core temperature and cardiovascular strain. |
| Humidity | A reduced water-vapour gradient limits sweat evaporation | Adaptations resemble heat acclimatization, including earlier sweating and plasma-volume expansion. However, high humidity limits evaporative heat loss, so sweat may drip from the skin without cooling the body. The athlete must reduce intensity and replace fluids and electrolytes. |
| Altitude | Lower atmospheric pressure reduces the partial pressure of oxygen, lowering arterial oxygen saturation | Ventilation initially increases. Over days, the kidneys release erythropoietin (EPO), stimulating red blood cell production and increasing haemoglobin concentration. Longer exposure may improve capillarization and the muscles' capacity to extract oxygen. |
These adaptations operate through negative feedback. Thermoreceptors detect changes in body temperature, while chemoreceptors detect altered blood oxygen, carbon dioxide and pH; control centres then activate effectors that oppose the disturbance.
A common misconception is that altitude contains a lower percentage of oxygen. The oxygen fraction remains about 20.9%, but lower atmospheric pressure reduces oxygen's partial pressure.
Exam Technique
For an HL response, distinguish an immediate response from chronic acclimatization and link each adaptation to its functional benefit. For example: “Increased plasma volume raises stroke volume, reducing heart rate at a given workload.” Avoid merely listing adaptations without explaining how they restore homeostasis.