Q: I love to squat but recently heard squats are bad for your knees. Should I stop squatting and substitute other exercises?

A: Don’t believe everything you hear. Studies have repeatedly shown the squat to be a safe, effective exercise; when performed properly, it poses little risk to those who have healthy patellar (kneecap) function. Even elite athletes who squat several times their bodyweight have few reported injuries directly attributable to the activity.

In fact, contrary to popular belief, squatting actually places less stress on the knee joint than leg extensions. This has to do with the way that force is applied during exercise performance. In the leg extension, loading is applied perpendicular to the long axis of the tibia – a fact that creates tremendous shear force in the patellar region. Alternatively, loading during the squat is mainly compressive, with forces applied parallel to the long axis of the tibia. Since a joint is better able to withstand forces from compression as opposed to shear, it therefore follows that squats are more joint-friendly than leg extensions.

What’s more, leg extensions tend to overstress the anterior cruciate ligament (ACL) of the knee. During performance, the quadriceps reacts by pulling the tibia forward (a phenomenon called tibial translation). The ACL, in turn, opposes the quadriceps by trying to prevent translation of the tibia. These two antithetic actions place a considerable amount of stress on the ACL and can potentially injure the ligament (and other soft tissue structures, as well).

Squats, on the other hand, have somewhat of a protective effect on the knee ligaments. Due to the multi-joint nature of the squatting movement (both the hip and knee are involved in performance), the hamstrings are activated as co-contractors and exert a counterregulatory effect on the pull of the quadriceps. The co-contraction of the hamstrings and quads help neutralize tibial translation, alleviating stress on the ACL.

All things considered, squats are a terrific exercise that works not only the lower body, but a significant portion of the torso, as well. Squat performance requires the assistance of many stabilizer muscles. Without the active participation of these stabilizers, the act of squatting simply cannot take place. Hence, while the glutes and thighs are the prime muscle movers, synergistic muscle action (muscles cooperatively work together) is derived from the abdominals, spinal erectors, rhomboids, trapezius, and other muscles. Squats, therefore, have a systemic effect on anabolism, helping to promote overall muscular development.

Further, the squat is an extremely functional exercise. It is used in many activities of daily living. Any time you lift an object from the floor, squatting is involved in the movement. Consequently, squats can help build the kind of practical strength and kinesthetic awareness that facilitates better performance of everyday tasks. In many cases, it can even help prevent lifting-related injuries at home and in the workplace. Now, this is not to say squats are appropriate for all populations. Conditions such as degenerative arthritis and various connective tissue disorders can be contra-indications for squatting movements. But it’s not the squat, per se, that is harmful; in these afflictions, any form of loaded (or even unloaded) knee flexion and extension can exacerbate a patellar-related injury. Hence, for those with pre-existing knee problems, caution must be utilized in both the choice and execution of thigh exercises. But as long as you have healthy knees, you should have no problem squatting on a regular basis.