Asked by: Pad Scanlon, London
It won’t make you stronger in the sense of building muscle in your heart or diaphragm, but holding your breath while training for certain sports has been shown to improve the ability of your muscles to cope with short, intense exertions. This works by increasing the concentration of bicarbonate in the blood, which helps to neutralise the lactic acid produced during anaerobic exercise. For this technique to work, you need to exhale normally and hold your breath when your lungs are empty, rather than taking a big breath in and holding that.
There are significant risks, though. A 2009 study found that free divers who regularly held their breath for several minutes had elevated levels of a protein called S100B in their blood, which is an indication of long-term brain damage.