Traditionally, you learn to squat from top to bottom, but many variables can limit your ability to squat well or to depth. For some, bad flexibility in the upper back, ankles, hips and calves are to blame, but it's also insufficient practice. These drills help you work on both. Reverse patterning is this idea of learning a movement in reverse. In a squat, the bottom half is where 99 per cent of people run into trouble because of poor technique, form or flexibility. Here these reverse patterning drills can help you groove better-looking and safer form at the bottom of your squat. Obviously, these drills are done without a barbell and they can also be a great way to warm up:
Toe Touch Squat
You first will need to be able to touch your toes, and for most, that's a matter of teaching yourself to bend at the hips rather than cranking your (probably tight) hamstrings. The toe touch squat drill teaches you to keep your back from rounding (which will probably happen at first), drive your hips down and get comfortable in the bottom position of the squat.
The dude in the video includes a "heel lift", which is done by placing plates (2kg will work) underneath your heels. The lift counters your poor ankle and calf flexibility to help you get into a deeper squat position.
Toe Touch Squat-to-Stand With Heel Lift
Once you can comfortably chill at the bottom position of a squat, it's time to practise standing up. Focus on pushing from your heels and maintaining a solid torso position the entire time. You can also try this without the heel lift, but that means you need a fairly mobile and strong upper back.
Do these drills for a few sets for five to six reps. You can check the rest of T-Nation's article for a few other variations and tips on where to go from there.
How to Fix a Really Ugly Squat [T-Nation]