For the big wave surfer, the ability to hold one's breath for long periods could mean the difference between a narrow escape and two lungs full of saltwater -- although practising underwater breath-holding is inherently dangerous, and should only be carried out under supervision. Here, in anticipation of this year's Red Bull Cape Fear event, big wave surfer Mark Mathews talks us through his underwater training regime, devised and implemented with the help of breath-holding specialist Nam Baldwin.