Dathan Ritzenhein, an Olympic distance runner for the United States, was starting to feel sick from his thyroid medication — a drug that was not medically necessary but one that his coach, a powerful and combative figure in the sport, had strongly recommended to improve his performance.

The coach was Alberto Salazar, a running legend himself who after his competitive career had teamed up with Nike, the world’s largest athletic apparel manufacturer, to train elite runners. He was dismissive when Ritzenhein expressed concerns, Ritzenhein later said under oath. Salazar was focused on revving Ritzenhein’s endocrine system for a coming race, he said, “instead of just whatever was best for my health.”

The tension between Ritzenhein and Salazar over medical issues and methods of performance enhancement was not uncommon in the Oregon Project, the vaunted team financed by Nike and led by Salazar that includes some of the world’s most celebrated runners. Ritzenhein’s experience, along with incidents involving several other athletes, were laid out in vivid detail in a confidential report written by the United States Anti-Doping Agency that was obtained by The New York Times.

The report, some aspects of which have been reported by The Times of London, describes, over 269 pages, a culture of coercion, secrecy and possible medical malpractice in the Oregon Project, an effort to make American distance running relevant again on the international stage.