Buchanan, a Sixth Degree black belt, says black belt gradings are as "tough as it gets".
"I have been a guest and officiated at gradings for well over 800 black belts and have never heard of anything as gruelling or as thorough as the process our students undergo," he said.
"We have five students under 13 in this twice yearly event, three of whom have attempted this challenge twice before. It is a measure of stamina, focus, discipline and spirit."
The gradings in Tauranga for the Mile High Karate Studios in New Zealand are a highlight for all the students as they have the opportunity to train with the Technical Director for New Zealand in Senior Master Paul Bryant - an Eight Degree black belt.
Mile High Karate was founded 35 years ago in Denver.