Ninety-year-old Carl Grove was tested after breaking an age group world record at the Masters Track National Championships last July, with his sample found to contain a metabolite of the banned substance trenbolone.

He was stripped of his national pursuit title and world record as a result but was not banned from competition as the United States Anti-Doping Agency (USADA) deemed the failure to be unintentional.

Instead, he accepted a public warning, the least serious punishment available, after it was deemed the drug "more likely than not" came from contaminated meat.

When it was revealed the nonagenarian had been tested USADA were criticised in some quarters for having questionable priorities, with Grove himself telling the Associated Press that they were "wasting their time" in testing someone of his age.

"What can I gain at 90-years-old doing drugs?" he is quoted as saying.

In response to the criticism, USADA chief executive Travis Tygart said the test had to be carried out because Grove broke a world record.

"Under the sport's rules, and track and field has a similar rule, in order for a world record to be ratified, the individual who broke the record has to be tested," he told VeloNews.

He went on to agree, however, that such athletes should not have to be tested.

"Cases like this, frankly, make us bang our head against the wall," he said.

"It's evidence of a system that needs to be fixed and overhauled.

"It's exactly why we've been pushing so hard for change to the World Anti-Doping Agency rules on these types of cases."

Now, in response to Tygart’s claims, WADA have told insidethegames the issue is "extremely complex".

"WADA is continuously striving to find the correct balance to ensure that positive anti-doping tests are catching cheats and not athletes who have inadvertently ingested a contaminated product," they said in a statement.

"It is an extremely complex area, in particular in countries where national laws permit use of substances for cattle fattening or with permissive regulations on dietary supplements, such as the United States.

"WADA and other anti-doping organisations have established research projects to address those issues from a scientific perspective and there is ongoing work by researchers and an independent committee looking into this issue with the goal of applying the fairest possible regulation while aiming at providing the strictest protection for clean athletes.

"In this regard, it would be very helpful if the chief executive of USADA concentrated his efforts on working more closely with the supplement industry in the US to ensure its products are free from contamination."

Tygart did say that USADA are testing supplements in his interview with VeloNews.

Contaminated meat is regularly cited by athletes as a reason for failed tests.

Last month Olympic race walk silver medallist Maria Guadalupe González from Mexico suggested a positive test for the same drug as Grove - trenbolone - could have come from contaminated meat.

Others to have blamed meat for failed tests include boxer Saul "Canelo" Alvarez, who tested positive for clenbuterol twice last February, and Estonian ice hockey player Marko Keltunen, who failed a test in November.

The most high profile recent case from the United States involved 27-year-old long and triple jumper Will Claye, who tested positive for clenbuterol in August.

He received no ban after USADA concluded the drug was "unlikely" to have come from anything other than contaminated meat.