Soleus Stretch
The soleus muscle in your lower leg is the most likely muscle to limit ankle range of motion when the knee is bent. When your knee is locked, your gastrocnemius muscles limit your ankle range. For squatting, the soleus is the target muscle.

Soleus Foam Rolling
Foam rolling the soleus muscle can help to improve ankle range of motion for the squat as it is the muscle most likely limiting ankle range. To get the soleus, aim midway and lower down your calf when foam rolling.

90/90 hip stretch
This is a go-to hip mobility drill that will improve hip range of motion into internal and external rotation. Stretching hip internal rotation is best performed without the hip in flexion as that is a range of motion naturally limited by bony structure.

Single Leg Bridges
When dealing with knee issues in the squat, strengthening the hips is a critical component. The single leg bridge provides direct hip and glute training with little extension stress on the low back.

4-Way Resisted Stepping
This exercise helps to strengthen the hips while under your own body weight. It can be used as an accessory lift to strengthen the hips and glutes for better control in squatting (and has applications for other lifts/exercises that require sufficient hip strength).

Posterior Hip Stretch
Stretching out the hip muscles can help to improve hip range of motion in the squat. When performing this stretch, avoid any pinching in the front of your hips. If you have pinching, find a way to change the angles of the stretch.

Off-set Loaded Split Squats
Improving hip strength helps to improve the squat. Off-set loaded split squats require hip abduction strengthening through a range of motion to control the torso. When someone has hip weakness, this is a go-to accessory exercise.

Squat Stance Modifications
The best stance for squatting will vary from one person to another. There are two variables to tweak: width and degree of toe out. Use different combinations of both of those to find the most comfortable stance that provides best depth without the knees caving in and back rounding.

Glute Ham Raise
In addition to classic back extensions, the glute ham raise provides added challenge for creating trunk stiffness and control around the knee joint.

Back Extensions
Direct low back and posterior chain training is often required and a best practice to include in any training program. If the low back easily rounds in the squat, it could be that the athlete just isn’t strong enough in their low back to control spinal positioning.