The shape of the Trap Bar and the position that you are in when gripping the handles puts you in a more upright, knee dominant position than you would be in the “hinged” hip dominant position you are in when doing a conventional deadlift where the bar is in front of you. This upright position shifts the emphasis of the exercise from the muscles that extend the hip, to the muscles that extend the knee-just like a squat. Additionally, standing within the bar reduces the back-stress problems that are experienced during squats as the bar is now in your hands rather than on your shoulders.