Front squats harm the knees. They fail to distribute forces evenly and the weight lies awkwardly across the front of the shoulders. This changes the squat for the worse. It forces the hip muscles to engage less. This includes the strong glute, adductor, and especially the hamstrings muscles.
Although the front squat challenges the core to maintain an upright torso, this does not offset the weaknesses. A well-rounded program addresses the core safely already.
The strictness in form it requires, often offered as an advantage, instead places great stress on the knees. Shear force occurs when you attempt to break a pencil using your hands. This force can destroy a joint. The front squat maximizes shear and causes anterior knee stress. This occurs as the knees surpass the toes too far.
The hamstrings attach to both the hip and the knee. During a front squat, the length of this muscle group stays too short due to the hip position. This bunches up the muscle fibers like a ball of yarn. It prevents the hamstrings from much involvement. This means less knee support.
Since the quadriceps on the front of the thigh remain engaged, this unbalances the forces on the knee. This occurs due to force on one side, but not the other. The quadriceps therefore place a dislocating force on the knee joint. During a regular squat and other athletic activities, both the hamstrings and quadriceps contract together to stabilize the knee. Try to jump as high as possible. Notice how the hips naturally push back as you descend. The body attempts to involve both the hip and knee muscles. Focusing on the quadriceps, or any muscle for that matter, invites joint stress. It does not represent natural movement.
Analyzing front squats bring up a major problem. Do not turn good compound exercises into isolation movements. This includes popular choices such as close-grip bench presses, wide grip pull-ups, and other extremes. Isolation is dangerous. Once again, this is because it places shear on the joints. Avoid anything unusual to safely develop all the involved muscles for an exercise. Stick with the basics using medium grips, stances, and positions. The back squat has its own challenges, but nonetheless distributes the load across all the involved muscles and joints well. More muscle works intensely. Muscles tend to work harder when working along with other muscles. It maximizes compression over shear forces. The joints and bones tolerate this much better. This avoids injuries, both nagging and sudden. Learn how to back squat with a barbell here.
The front squat’s popularity comes from Olympic weightlifters. The squat more closely mimics the bottom position required for their lifts, the snatch along with the clean and jerk. This application has no relevance to the average trainee.
Olympic weightlifting influenced early resistance training. It still has a strong hold on today’s methods. Some strength coaches therefore justify and use it to keep with tradition. Bodybuilders also use it to emphasize the quads. Some do it for variety, in a misguided attempt to confuse the body.
Progress itself creates variation though. Adding harmful exercises to vary things will only allow unnecessary risks. Any exercise that generates tension can build size and strength. Front squats, like any heavy exercise, can therefore build muscle. Still, you should instead develop all the involved muscles during an exercise safely. Distribute the load evenly. This keeps you safe and builds strength just as well.
Stick with the back squat and ignore the front squat. Ignore popular advice. The back squat represents the only lower body movement you need. Your knees along with your overall strength and size will benefit from this advice.