Duval: I have taken Creatine

However, reports this week of a new athletics drugs scandal will add urgency to the informal investigation into performance-enhancing drugs instigated by the Royal and Ancient Golf Club, the sport's governing body apart from in the USA and Mexico.

Duval, who begins his defence of the Open title on Thursday, revealed details of his extensive fitness regime in this month's Golf Digest.

The 30-year-old America lost 40lb and four inches off his waistline by undertaking regular exercise, gym work, weight-lifting, stretching and mountain bike riding.

But regarding the use of supplements, Duval said: "I am always searching for an edge, so my strength coach and I try to evaluate everything that's out there. So far, Creatine is the only dietary supplement we know of that has been shown to affect fast-twitch muscle fibres. Since golf is an explosive sport, we feel it may have some benefit."

Creatine is not a banned substance and no suggestion has been made that Duval has taken anything illegal.

But, with cheques such as the £700,000 on offer to the Open winner, there are fears that others might take that search "for an edge" to extremes. Australian Craig Parry has caused controversy by claiming that three winners of golf 's major tournaments used beta blockers, which are said to help ease tension.

The use of Creatine in sport is widely recognised. The England World Cup team managed by Glenn Hoddle were encouraged to take it to help the recovery process after matches. Boxers and athletes also endorse Creatine products.

Cave, who has seen publicity material for the new Golf Advantage Creatine Serum, believes that, for the moment, his sport is "more than relatively clean".

But he added: "With the length they drive now, certain individuals might be tempted to take something that enhances their body and muscle mass."