[1] Kaminaga was born in Sendai, Miyagi Prefecture,[2] and began learning judo during high school; a considerably late start for a top competitor.

Kaminaga improved his techniques at a quick pace, and took a dan rank exam at the Kodokan Institute at the suggestion of his colleagues during his senior year in high school.

However, Kaminaga was completely outclassed when he participated in the Meiji University judo team's sparring sessions.

Kaminaga become the head coach of the Meiji University judo team in 1968 at the advice of Koji Sone,[3] where he taught future Olympic gold medalist Haruki Uemura.

He also served as a coach of the Japanese judo team for the 1972 Summer Olympics, but resigned from his post at Meiji University after one of his pupils, Masatoshi Shinomaki, lost in the preliminary round of the tournament.