What you feel: Knee pain (especially around the knee cap), low back pain

In the case of the squat, your knees collapse inward. Valgus( a deformity involving oblique displacement of part of a limb away from the midline) damaging putting side-to-side stress on your joint, particularly on your patellar tendon.

If your knees cave in it's due to a set of weak glutes.

When your glutes aren’t as strong as they need to be to handle the load on your back, your knees automatically fall inward to help you lift the weight. It's okay if it happens only occasionally, like on the last rep of your set while setting a new max. (You’ll see some powerlifters’ knees go inward onsets when they’re risking.) But besides that, don't let it happen too often.

Making matters worse, having weak glutes can cause you to lean too far forward when you squat. While a little bit of a forward lean is OK, having too much of one can put excess pressure on your lower back.

There’s one more thing that can cause you to lean forward excessively when you squat: reduced ankle mobility. You’ll know this is your problem if you feel that it’s challenging to keep your heels on the floor as you lower your butt.

Are you having knee pain? Get A STRONGER BUTT!

What to do first is simple: “Develop a stronger butt to save your knees,” Building up your glutes will help your knees track correctly. To strengthen them, try adding glute bridges, and hip thrusts to your workouts.

If you have a bar on your back, focus on pulling it down into your traps. That will help stabilize the upper part of your torso and prevent it from tipping forward.

If you’re having a hard time keeping your heels on the floor, foam roll, stretch and do mobility drills for your calves before squats. Try warming up the calf's and putting them through their full range of motion with calf raises.

Also, you don’t need to squat with a barbell on your back. Mix it up and perform goblet squats, which are usually performed with a dumbbell or kettlebell are the variation that is knee and back-friendly, and it makes it easier to squat without your knees collapsing or body leaning forward.