Physical Training Instructor (PTI) is a term used primarily in the British Armed Forces and British police for an instructor in physical fitness.
In the Army, there is a separate branch, such as the Army Physical Training Corps, who oversee physical training and manage military gymnasiums; and are attached to individual units. They are assisted by All Arm Physical Training Instructors (AAPTIs), who are qualified, but are not specialists, have other jobs within the unit, and are not drawn from the APTC.
PTIs in the Royal Navy are known as "club swingers" or "clubs" from the crossed clubs they wear as a rate badge. In the Army, however, the PTI badge consists of crossed swords.
The original article can be found at Physical Training Instructor and the edit history here.