Albert Barnes Commentary 1 Chronicles 11:10

"Now these are the chief of the mighty men whom David had, who showed themselves strong with him in his kingdom, together with all Israel, to make him king, according to the word of Jehovah concerning Israel." — 1 Chronicles 11:10 (ASV)

Strengthened themselves—or “exerted themselves”—meaning they “strenuously assisted with all Israel in making David king.” This list of David’s principal heroes, therefore, belongs to his reign at Hebron. In Samuel, the list is not given until nearly the end of David’s reign (2 Samuel 23:8–39).