University of Iowa football coach Kirk Ferentz addresses the media on Wednesday, Feb. 2, 2011, at the Jacobson Athletic Building in Iowa City. (Liz Martin/The Gazette)

The 13 Iowa football players hospitalized for a muscle disorder following grueling offseason workouts are expected to participate in spring practice next month.

The Des Moines Register reports that assistant coach Eric Johnson told people attending a booster function Tuesday night that the players are fairly healthy and back in class.

Johnson says the players are slowly getting back into the flow of offseason workouts.

University of Iowa leaders have launched a 90-day investigation into why the players contracted rhabdomyolysis, a stress-induced syndrome that can damage cells and cause kidney problems.

Iowa Coach Kirk Ferentz told reporters last week that he remains puzzled about what caused the disorder, though he says the workouts in question won’t be repeated.