Ahimaaz was a well-known runner 2 Samuel 18:27. Speed was a heroic virtue in those simple times (compare 2 Samuel 2:18). In Hezekiah’s reign 2 Chronicles 30:6, 2 Chronicles 30:10 we find an establishment of running post-men; and the same name (“runners”) is given Esther 3:13 to the Persian posts, though at that time they rode on mules and camels.
Bear tidings - The original word is used almost exclusively of bearing good tidings, and hence, is rendered in the Septuagint (though not always) εὐαγγίζεσθαι euangelizesthai 2 Samuel 4:10; 1 Samuel 31:9. In 2 Samuel 18:21, it is not “carry the good tidings,” but “tell,” simply “announce.”