Studying anatomy and biomechanics is not something that every sports science student or strength coach likes to do. But in order to create a sound training program, coaches need to understand the basic laws of functional anatomy and biomechanics. When talking about the squat, one very important phenomenon to understand is the Lombard’s paradox. The quadriceps and hamstrings are located on the opposite sides of the human body, making them antagonist muscle groups. The quadriceps role is to extend the knees and flex the hips. The hamstrings flex the knees and, together with the glutes, extend the hips. The Lombard’s paradox explains why the squat cannot be considered as only a ‘quads exercise’. So, the question is how can antagonist muscle groups lead to one movement?
The squat is a complex movement in which multiple joints act together. Therefore, functional anatomy plays a crucial role in performing squats. The quadricep is a muscle group that crosses two joints, same goes for the hamstring and glute muscles. Because of the muscles’ origins and insertions, different moment arms appear during the concentric part of the squat. Basic laws of biomechanics state that the greater moment arm produces the movement. The quadriceps has a greater moment arm over the knee than the hamstrings. On the other hand, the hamstrings and glutes have a greater moment arm over the hips than the quadriceps. This means that contractions of the hamstrings/glutes and quadriceps will result in hip and knee extension. With the help of stabilizers (spine erectors and core muscles), humans are able to stand up from the squatting position while keeping the spine in its natural position.
In practice, one situation can cause a bit of confusion. Since both muscle groups act together, why then is it possible to have greater muscle soreness in the quads rather than the glutes and hamstrings after intense squatting practice? The answer lies in the body mechanics when performing squats. Some people tend to initiate the movement from the hips while the others do it from the knees. Hip dominant squatters will load their posterior chain (i.e. glutes and hamstrings) much more since the knees do not travel forward too much. Knee dominant squatters drive their knees forward and out, placing more demand on the anterior chain (i.e. quadriceps).
If you are asking yourself which of the two is better, I would answer that both ways are excellent. The only question you have to ask yourself is why you squat. If you want to develop strength and power in your hips perform the hip dominant squat. If you want to gain muscle mass in your quads, go for the knee dominance.
Whatever you choose, remember that the squat is a natural movement and it is a very beneficial exercise for both recreational athletes and professional sportsmen. If you perform squats with medicine balls, kettlebells or barbells, be aware of your technique and choose an appropriate load.
Next time read about misconception #2: Squats can hurt the lower back