There are many conditions of the upper airway tract in the horse that are subtle and difficult to diagnose in a standing horse (static endoscopy). If respiratory noise or difficult breathing exists in the face of normal static endoscopy, the diagnosis might need to be made while watching the inside of the upper airway while the horse is exercising.

This can now be done two ways. The traditional way (past 20 years) has been endoscopy of the upper airway while the horse is exercising at speed on a treadmill. Since about 2005, equipment has been developed that can be attached to the horse's halter and allows visualization of the upper airway in the "over ground" exercising horse under saddle. As of the time of this writing, these systems are becoming more practical and affordable.