Single Leg Box Jumps

In 2000 (and on a few other occasions) I published and claimed copyright on this exercise description (bolding added now):

Single Leg Box Jumps:

Stand on one leg facing a small box. Jump explosively on to the top of the box. Drop down and repeat.

I was conducting research and I came upon the following exercise in a publication copyright claimed by another 'author' at a subsequent date (bolding added):

Single Leg Box Jumps:

Stand on one leg facing a small box. Jump explosively on to the top of the box. Drop down and repeat.

And I said to myself: “That looks familiar!” So I cross-referenced it and I said to myself: “Wow! No wonder that looked familiar!”

And I came upon this description another two more times by the same 'author' in different publications.

I noted that the use of this description was in the absence of credits or references to the origin or permission to use from the original author (myself), and that the 'author' claimed copyright....