Spokesman Tom Moore said Wednesday the players have rhabdomyolysis, a stress-induced muscle syndrome that can damage cells and cause kidney failure in severe cases.
Moore says the cause of the disorder has not yet been determined. All of the players, however, had participated in winter workouts.
University of Iowa physician John Stokes says the common denominator is they had all participated in strenuous exercise, which commonly brings on the disorder in otherwise healthy young people. The school said the players, whom they would not identify, were "in safe and stable condition" and responding well to treatment.