EUGENE, Ore. (AP) — The U.S. Olympic track and field trials take to the starting line this week amid another high-profile doping case. Shelby Houlihan, the American record holder in the 1,500 and the 5,000 meters, was considered a strong Olympic medal contender. But she won’t race at trials. She received a four-year doping ban for what she says was nothing more than eating a burrito that was laced with traces of the performance-enhancing drug nandrolone. Many of these cases never result in sanctions like this. But international antidoping authorities pressed the case and went for the full ban. The head of the U.S. Anti-Doping Agency, Travis Tygart, says the rules need to be changed to allow more leniency to people who inadvertently ingest banned substances.