There's a few things that can affect the ability to do squats correctly, and it is a surprisingly hard lift to do. Take heart, all the issues are correctable. They range from:
- Flexibility issues--hip, hamstrings, glutes, and calf muscles can all limit range of motion
- Skeletal structure issues--if your stance is too wide you will be fighting your skeleton to get deep
- Body position and technique issues--using guides can help you fix these.
I'd be hesitant to believe that your Achilles tendons are to blame. The only kid I know to truly have that problem was constantly on his tip-toes before his surgery. Even now he has a hard time changing how he walks and runs because he's been like that so long.
However, flexibility can be an issue. This article explains roughly what I did to perform some squat rehab myself. In preparation to fix your squats, I recommend getting a couple pieces of training equipment:
- Get yourself a TUBOW (Terribly Useful Block Of Wood)
- Find a platform or a box that can support your weight that is at the depth you want to get to. NOTE: proper depth really has to be measured while under tension. I found out that below parallel when I'm relaxed isn't the same when my legs are tense.
- Get a little hand held video recorder to see your form for yourself.
You can work on your stretching right away, but when you go to your squats you'll have to do some set up work:
- Find a depth you feel like you can get to to on the box using the empty bar as you sit back on to it. You may have to stack some weights on it to get a little higher than parallel.
- Sit on the box and set up the TUBOW so that it is touching your foot and your knee.
- For each warmup set and your current work set align your foot to the TUBOW, and squat down to the platform.
You'll be repeating this exercise, removing a layer of weights until you can get to the proper depth. During this time, resist the temptation to add weights. Every inch of depth adds a lot more work that you have to do.
Lastly, on the note of structural issues, if you feel pain in your hips and it doesn't feel like a stretch, you might have too wide of a stance for your body. I found that I need to keep my feet no more than shoulder width apart, and push my knees out as I go in and out of the hole to do the squat properly.
I was able to fix my issues in about four sessions, but that was because I already put in a lot of work with stretching. You can see my progress here:
- First attempt: still not deep enough, but better than I was doing with another 60lb on the bar
- Second attempt: got really close, but that extra weight on the platform was just above parallel.
- Third attempt: no video, this is where I discovered my skeletal structure issues and the pain from this attempt caused me to stall. I was so disgusted I burned the video and didn't even want to get feedback on it.
- Fourth attempt: finally hit below parallel, and felt really good doing it.
While some people do better with the raised heel of a proper weightlifting shoe, you don't necessarily need it to fix your problems. Now if your range of motion is limited by inflexibilities, it can take between 4-6 weeks to build the range of motion you need. It is possible, but be smart about how you do it.