מַשְׂכִּ֗יל לְאָ֫סָ֥ף הַאֲזִ֣ינָה עַ֭מִּי תּוֹרָתִ֑י הַטּ֥וּ אָ֝זְנְכֶ֗ם לְאִמְרֵי־פִֽי׃
Maskîl d’Assaph. Écoute, ô mon peuple, mon enseignement, prête l’oreille aux paroles de ma bouche.
Rashi
ויט שכמו AND HE INCLINED HIS SHOULDER — he lowered his shoulder; similar are, (2 Samuel 22:10) “He bowed (ויט) the heavens” and (Psalms 78:1) “Incline (הטו) your ear”. Onkelos, however, explains it differently: HE BOWED HIS SHOULDER to wage wars and to conquer new districts — for he (Issachar) dwelt on the marches — AND the enemy BECAME subject to him AS A SERVANT TO PAY TRIBUTE.