Most, but not all, states require that Athletic Trainers practice under the direction of a medical professional. These directions are often called Standing Physician's Orders.
Standing Orders requirements vary significantly from state to state. Most states do not require written orders, but some do. In some states the Standing Orders must come from a physician, if other states Standing Orders may also be issued by a dentist, podiatrist, or registered nurse.
It is of the utmost importance that you read and understand your state's Athletic Trainer Practice Act and the Standing Orders requirements in it.
The NATA provides information on every state practice act on its website - AVAILABLE HERE.