Boxers who have done Isometrics or Muscle Control in their regimens?

For those who are familiar with resistance exercises like isometrics and also muscle control what boxers do you know have done them? I once hear Jack Dempsey did some resistance exercises and some muscle control. So I did some more research and found the old Article on the Magazine Muscle Builder back in February 1925 ***********.sandowplus.co.uk/Macfadden/MuscleBuilder/Feb25/mb-Feb25-01.htm

Here's also a quote from Dempsey:

"Too many people believe that they are giving their muscles all of the exercise they require if they merely go through the motions which they have adopted from textbooks or in which they have been coached by gym instructors. That just isn't so. Too obtain the best results, every exercise movement should be done in a thoroughly business-like manner. The muscles should be tensed, made to move so that the person actually can feel the resistance."

So that was a confirmation that he did some sort of resistance training. What are your thoughts Classic Forum?