Front squat – Hi-bar back squat – low-bar back squat. Note the differences in knee and hip deflection/movement allowing the bar to remain centered over the mid-foot balance point. Notice how as the back becomes more vertical in the front squat, the knees are pushed further forward and knee movement is increased. Of all three positions, the front squat actually requires the least forward lean to keep the bar over the middle of the foot.

However, notice what this does the moment arms are involved in the movement. The arms between the hips and the bar is greatly shortened and between the knees and the bar is greatly elongated. This essentially produces a squat that is relatively easy in terms of hip extension but extremely difficult in terms of knee extension. This is why the front squat has a reputation as a great quad builder.

Jay Amra of AMLOT doing squats