The world of doping has always been murky and complicated; if it is at all possible, it has become even more labyrinthine in recent weeks.

In the aftermath of last month's Sochi Winter Olympics, reports emerged that a number of Russian athletes had been using xenon gas to enhance their performance.

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Xenon is not a banned substance under the World Anti-Doping Agency (WADA) code, but research suggests that inhaling the gas boosts the body's production of a protein known as HIF1A. Put simply, HIF1A seems to act by stimulating the production of other compounds in the body, including Erythropoietin(EPO).

Stimulating EPO encourages the production of more red blood cells which, in turn, means an increased ability to transport oxygen around the body. This, in theory at least, leads to an increase in athletic performance, particularly in endurance sports.

It is EPO which has been the scourge of road cycling over the past two decades. Synthetic EPO has been banned since the early 1990s but experts are divided over whether inhaling xenon is illegal under the WADA code.

The code currently states that substances which "artificially enhance the uptake, transport or delivery of oxygen, excluding supplemental oxygen", are prohibited.

This is where the grey area is. Research by Dr Ben Koh and Matt de Neef for the Cycling Tips website attempted to clarify the situation as to whether or not xenon gas should be classed as a performance-enhancing drug but the situation is not straightforward.

Koh and Neef established that for WADA to successfully prosecute an anti-doping violation, the Court of Arbitration for Sport need to be "comfortably satisfied" that the procedure of inhaling xenon gas is scientifically proven to increase oxygen transfer but the current scientific evidence about the effect of xenon gas on oxygen transfer is tenuous at best. Xenon gas is currently used as an anesthetic but little conclusive research has been done on its ability to improve athletic performance.

Yet Dick Pound, former president of WADA said "let us realise, without doubt, that this is doping and it is impossible to say……that the rules are not clear," apparently convinced that taking xenon should not be permitted.

Similarly, Prentice Steffen MD, head physician at the professional cycling team Garmin-Sharp, feels that xenon is not morally justifiable. Despite not being on the banned list, Steffen feels that the substance simulates the effects of doping therefore crossing an ethical boundary, and thus refuses to administer it to his athletes.

The Russian authorities however, seem convinced in some quarters at least, that there is a benefit for their athletes to take xenon. During the 2014 Winter Olympics, German television alleged that Russian athletes have been using xenon since the 2004 Athens Olympics right through to the Sochi Winter Olympics last month, where the team topped the medal table with 13 golds.

Of the 22 Russian athletes who won medals at the 2006 Winter Olympics, 15 had used a xenon-based mixture of gases as part of their preparation - a preparation programme that had been officially approved by the Russian government.

Other media reports suggested that a Russian defence ministry report, written in 2010, set out guidelines for administering the gas to athletes. Russian authorities staunchly defend their right to administer xenon to their athletes with Vladimir Uiba, the head of Russia's federal biomedical agency, insisting that his country has done nothing wrong.

"Xenon is not an illegal gas," he said. "We have a principle not to use what is forbidden by WADA. It is possible that our sportsmen have been using xenon inhalators but there is nothing wrong with that. We use what is not illegal, is not destructive and does not have side-effects."

Yet the feeling remains that there is something of an inconsistency within the rules here. This case, again, raises questions as to which practices constitute doping and which do not.

When Koh and Neef analysed which drugs are prohibited within sport, the situation became even more unclear. They found that caffeine used to be on WADA's banned list yet no longer is and anti-inflammatory painkiller medications as well as paracetamol have been known to be abused by athletes to help improve their performance, but these are not prohibited. Also, altitude training and hypoxic training tents have a similar effect on athletes as EPO- they increase the red blood cell count- yet they are not banned by WADA.

WADA president, Scot Craig Reedie, has promised that his organisation will imminently look at the issue of xenon gas, saying: "The topic of gas will be addressed at the next meeting after the Olympics."

Yet there is the pervading feeling that action is too sluggish in circumstances such as this. It remains unclear whether or not xenon produces significant performance-enhancing effects but there can be little doubt that athletes will push the boundaries as far as is humanly possible in their quest to gain an edge over their rivals.

It has been witnessed time and time again that athletes will cheat, particularly if they feel little threat of being caught, so it should come as little surprise that athletes will use a substance which is not even prohibited but still has the potential to improve performance. Xenon may not be on WADA's banned list, but sport needs moral boundaries too, and inhaling xenon seems to push those boundaries just too far.

Dr Ben Koh and Matt de Neef's report is available here