It is not clear how John came to enlist as a gymnastics instructor, but in his army medical records it states his condition (cardiac hypertropy) was "the result of nineteen years or more or less continuous athletic strain", and also in his military records is a letter addressed to him requesting he enlist in the army gymnastics staff for the duration of the war. Both of these instances suggest he was involved in gymnastics training either as a career before he trained as a dentist, or as a hobby alongside his dentistry career.