The key adaptation to heat acclimatisation is:Group of answer choicescardiac hypertrophyexpanded blood volumereduced sweat sensitivity

The key adaptation to heat acclimatization is expanded blood volume.

Here's why:

1. Heat acclimatization is the process by which the body adapts to high temperatures over time. This process involves several physiological changes.

2. One of the most important changes is the expansion of blood volume. This happens because the body needs to cool itself down in hot conditions, and one of the ways it does this is by sending more blood to the skin where it can be cooled by sweat evaporation.

3. As the body gets used to the heat, it starts to produce more blood to facilitate this cooling process. This is why expanded blood volume is considered a key adaptation to heat acclimatization.

4. While cardiac hypertrophy (enlargement of the heart muscle) and reduced sweat sensitivity can also occur as a result of heat acclimatization, they are not considered the key adaptation. Cardiac hypertrophy can help the heart pump more blood, but it's not a direct response to heat. Reduced sweat sensitivity means the body becomes more efficient at sweating, but this is a secondary adaptation that happens after the blood volume has already expanded.