Rashi on Genesis
וישתחו ארצה HE PROSTRATED HIMSELF — From this we may learn that we should thank God for good news (Genesis Rabbah 60:6).
Radak on Genesis
ויהי..וישתחו ארצה, prostrating himself on the ground with arms and feet extended.
Haamek Davar on Genesis
And he prostrated towards the earth for God - Not just bending the knees, rather, he fell with his entire body to the land given his happiness and gratitude.