Heather warming up.
"Front squatting is brutally hard. Moving the barbell placement from thespine of the scapula as in the back squat, to the front rack position and away from the athlete's center of gravity effectively generates an additive crushing rotational force to an already demanding hip and leg extension movement. Moving loads further and further away from the spine forces the athlete to resist trunk flexion while simultaneously maintaining a rigid spine-pelvis relationship. Herein lies the beauty of this greatly hated squat variation." Kelly Starrett
Read his complete post about the front squat compromise on San Francisco CrossFit's Blog