Just a week before the onset of the US Olympic Track and Field Trials 2021, American middle-distance runner Shelby Houlihan has been handed a four-year ban. Shelby currently holds the American record for women's 1500m (3:54.99) and 5000m (14:23.92) races.Shelby tested positive for nandrolone, an androgen and anabolic steroid responsible for increasing muscle mass, in an out-of-competition test held on December 15, 2020.The Athletics Integrity Unit (AIU) informed Shelby on January 14th, 2021 that she was provisionally suspended for testing positive for the banned substance. As a result, she wasn't able to participate in a single event in 2021.At the 2016 Rio Olympics, Shelby finished in 11th spot in the women's 5000m race. Three years later at the 2019 Doha World Championships, she finished in fourth position in the women's 1500m race.Shelby Houlihan was supposed to compete in the women's 1500m and 5000m events in the US Olympic Track and Field Trials 2021 and was considered a medal prospect for the Tokyo Olympics.Shelby Houlihan, the U.S. record holder in the 1500m & 5000m, tested positive for the banned substance Nandrolone from a Dec. test & is banned for 4 years. No Olympic Trials. Says the positive test came from contaminated meat in a burrito. Appealed AIU's decision to CAS & lost. pic.twitter.com/MZs7pskQNH— Chris Chavez (@ChrisChavez) June 14, 2021Also Read: Team USA's Rio Olympic champion Brianna Rollins-McNeal banned for five yearsShelby Houlihan claims innocenceShelby Houlihan poses with her medal after winning the Women's 3000m during the 2020 USATF Indoor Championships (Photo by Christian Petersen/Getty Images)Despite the doping allegations, Shelby Houlihan has maintained her innocence. According to WADA, consuming pork can lead to an athlete testing falsely positive for nandrolone as certain breeds of pigs produce high amounts of it naturally.Shelby explained in an Instagram post that the likely source of nandrolone was a burrito ingested ten hours before the test from a Mexican food truck that serves pig offal.To further strengthen her case, Shelby also passed polygraph tests and had her hair sampled by one of the world's foremost toxicologists. However, on June 11th, the Court of Arbitration for Sports sentenced her to a four-year ban. View this post on Instagram A post shared by Shelby Houlihan (@shelbo800)Also Read: Sifan Hassan "happy" that Letesenbet Gidey broke her women's 10000m world recordOnly the top three athletes finishing in the US Olympic Track and Field Trials 2021 will get the opportunity to represent the country at the Tokyo Olympics.In the women's 1500m race of the US Olympic Track and Field Trials 2021, Elinor Purrier St. Pierre and Jennifer Simpson are the favorites to clinch two of the three spots. Karissa Schweizer, on the other hand, will be eyeing a Tokyo berth in the women's 5000m race.