A new study suggests that 56 percent of N.F.L. players would be considered obese by some medical standards.

The N.F.L. called the study faulty for using players' body mass index, a height-to-weight ratio that does not consider muscle versus fat. The players union said that despite the familiar sight of bulging football jerseys, there was no proof that obesity was rampant in the league.

Joyce Harp, the University of North Carolina endocrinologist who conducted the study, acknowledged that without measuring body composition, it was uncertain how many players were truly fat, but she said it was unlikely that the high body mass indexes were "due to a healthy increase in muscle mass alone."

The study appeared yesterday in the Journal of the American Medical Association.

John Jurkovic, a former defensive tackle, said he had seen plenty of evidence that players had become not just bigger but also sometimes fatter, "big as houses" in recent years because of league pressure to intimidate opponents and win.