Competitive Apnoea (breath-hold) involves participants holding their breath in water with disciplines that relate to maximum duration of breath hold, the horizontal distance covered whilst immersed and holding breath in a swimming pool and the maximum depth achieved whilst diving. Breath-hold divers are known to have larger lungs and better oxygen carrying capacity than the average person; adaptations which suggest that apnoea training may be an effective alternative pre-acclimation strategy for high altitude exposure. It is known that breath-hold diving improves the contractility of your spleen. The spleen contains a store of red blood cells and when the human body is in a hypoxic situation it contracts to release its red blood cells to help cope with the lack of oxygen. By increasing the contractility of the spleen through breath hold training we hope to reduce the effects of the low levels of oxygen associated with high altitude. Breath-hold training can take place with very little specialist equipment in the comfort of your own home making it a possible acclimation method that is available to everyone. The potential benefits may also be advantageous for military personnel being deployed at short notice to high altitude. Therefore this study aims to assess the effectiveness of breath-hold training as a way to prepare for a high altitude expedition.