This is really an athletic pose and needs strong arms of her and even stronger thighs of him. When she arches her back a little, she gets better thrust from him.
Steps to perform:
Step 1: He holds her thighs and with his support she rests palms on the ground.
Step 2: Meanwhile, he adjusts himself closer to her groin.
Step 3: He now gets the momentum to slide in and out.