Single-leg squats can be an incredibly effective exercise to develop stability in the knee, which in turn builds strength and will reduce the chances of knee injuries. To maintain proper stability of the knee through a single-leg squat, you'll need correct positioning, flexible and mobile hips and ankles, and lateral stability in the adductors and abductors. When performed correctly, single-leg squats are incredibly functional exercises for developing knee stability.
Proper Shin Angles
The first component to a strong single-leg squat is to make sure the leg and knee levers follow the correct angles for a technically sound movement. To perform a correct single-leg squat the knee should not move past the toes, as this will put extra pressure on the anterior cruciate ligament, or ACL. A full squat is reached when the thigh is parallel to the ground; the shin should remain parallel with the torso throughout the movement. The knee should not rotate medially or laterally, but should be linear throughout the squat.
Hip and Ankle Mobility
Knee stability, especially in a single-leg squatting movement, is influenced by the mobility of the hips and ankles. Tight hips or ankles often cause compensation at the knee and result in poor stability. Prior to performing single-leg squats, practice a thorough warm-up including hip and ankle exercises such as calf stretches and leg swings. When the knee hinges and moves through flexion and extension around the patella, mobile hips and ankles will make the movement more efficient.
Lateral stability is of the utmost importance when performing a single leg squat to prevent damage to the medial and lateral collateral ligaments, or MCL and LCL. Stability of these ligaments can be increased by strengthening the hips, adductors and abductors to improve strength in the sagittal plane. It is common in single-leg squats to see a valgus collapse, or the knee drifting medially. This instability is often caused by poor mobility in the hips and ankles, and should be addressed and prevented.
Correct postural positioning in a single-leg squat relates to knee stability as it has a direct correlation to hip function and a correct shin angle. Correct posture places the center of gravity over the weight-bearing leg, minimizing over-compensation of the knee for poor core positioning. Proper posture will also engage the anterior core muscles and engage the hips in proper pelvic position. Finally, correct posture will align the torso with the shins creating the correct angles for the knee levers to complete the squat.