Readings

Meanwhile, down at the deep end

Tanya Streeter can hold her breath for five and a half minutes. In that time she turns blue and has blood oxygen levels only seen in people who have had cardiac arrest. It took Tanya three minutes and thirty eight seconds to descend to a depth of 400ft below sea level before returning to the surface unaided. She holds the world record for this feat with no-one else getting anywhere near. She is the Paula Radcliffe of free diving.

Try holding your breath and your body will gasp for air because of three things: a shortage of oxygen, a build up of carbon dioxide and the demands of stretch receptors around the lungs. These work together to sense each intake of breath and tell the brain when another is due. The secret of not breathing is to blunt the impact of the stretch receptors. One way of doing this is to take long slow breaths through tightly pursed lips - like you do when you catch your child doing something they shouldn't. In laboratory tests Tanya Streeter was connected to a machine which measured blood oxygen levels. Most people have around 98%. Anything below 80% is considered dangerous. After five and a half minutes Tanya's went much lower to below 50%, which was off the machine's scale and a level considered incompatible with human life. Bet she doesn't train in front of a mirror…