[dionidium]

I'm not sure why you'd insist on an eccentric interpretation of "strong" in the context of this quote. It's a common English word that means, "having the power to move heavy weights or perform other physically demanding tasks" or "able to withstand great force or pressure."

Synonyms include: powerful, muscular, sturdy, robust, tough, rugged, stalwart, hardy.

In ordinary English these terms can be applied to mental as well as physical fortitude.

The meaning here is not opaque.