CANBERRA, Australia - An Australian sports scientist who helped develop a test to detect EPO thinks the abuse by athletes of legal performance-enhancing substances could become a major issue of the Beijing Olympics.

"Beijing will probably be remembered for the abuse of legal drugs like Viagra," Robin Parisotto told Australian Broadcasting Corp. radio on Friday. "Any physical activity that goes for longer than two minutes would be a beneficiary of something like Viagra, just like the normal blood doping drugs."

The World Anti-Doping Agency is investigating whether or not to include Viagra on its list of banned substances, but no decision will be taking until after the Aug. 8-24 Beijing Olympics.

EPO, a synthetic hormone which enhances endurance by stimulating the production of oxygen-rich red blood cells, is among the main drugs of choice among cheaters.

Parisotto, who helped design the first recognized EPO test before the Sydney 2000 Olympics, said Viagra had the same benefits as blood doping because of its circulatory effects "and not only in the private parts."

Other substances, like psychological medication, can also enhance performance, Parisotto said.

"To take a drug which will keep your mind clear and focused certainly is another area of drug-taking that would be of benefit to athletes."

Experts are divided over whether Viagra actually offers athletes an edge.

Some sports authorities say the drug is now finding a following among athletes. It isn't clear how many might be taking it in hopes of improving athletic performance.

Viagra, also known as sildenafil, is manufactured by Pfizer Inc. It originally was developed as a heart drug. Its use as a treatment for erectile dysfunction was accidentally discovered.

The drug works by increasing the effects of nitric oxide, which makes blood vessels expand. That should theoretically allow blood cells to get more oxygen from the lungs. It also might improve heart function.

Viagra also is approved to treat pulmonary hypertension, a condition in which the lungs' blood vessels tighten. Doctors have used the drug experimentally to treat pregnant women with high blood pressure and to ward off jet lag.

But whether Viagra makes athletes faster, higher or stronger is uncertain.

"Just because you have more nitric oxide doesn't mean that you are going to be a better athlete," said Anthony Butch, director of the Olympic Analytical laboratory at UCLA. "If you have all the nitric oxide you need, and if you generate more from Viagra, it's not clear what effect that would have."

Some preliminary studies have shown that cyclists taking Viagra improved their performances by up to 40 percent.

"If you have more oxygen going to your muscles, that's more energy and that makes you a better athlete," said Dr. Andrew McCullough, a sexual health expert at the New York University School of Medicine. "Even if it only gives you a 10 percent increase, in peak athletes that is enough to win."

McCullough said Viagra is only likely to help athletes such as runners, cyclists or skiers _ sports where endurance and speed are key. Viagra does not work directly on muscles, so will not make athletes stronger.