Good exercises involve multiple joints through the full range of motion and recruit lots of muscle mass. The low-bar back-squat does this. It is often thought that the squat is a leg exercise about equivalent to what is done in leg press machines. This idea is not true. The squat involves the ankle, knee, hip, and shoulder joints. The back is heavily trained during squatting just like all the muscles that control flexion and extension of the joints listed in the preceding sentence. Yes even the shoulders are worked, especially if the low-bar version of the squat is used.
Low-bar and High-bar
The bar can be held on either the trapezius muscles (high-bar position), or trapped between the hands and the posterior deltoids (low-bar position). The high-bar position is the way anyone will put the bar on their back unless someone tells them otherwise. The high-bar squat is preferred by olympic weightlifters. The low-bar squat is used by powerlifters. Here is Justin Lascek, senior editor of 70sbig.com squatting 485 using the low bar style. In contrast here are some olympic lifters at California Strength doing some high-bar squats. You'll notice the difference in bar position and in the back angle (the angle made between the torso and the horizontal floor). The low-bar squat requires a greater forward lean and therefore appears bent over. This is simply a result of keeping the bar in balance. In order for a heavily loaded bar to be balanced it must be positioned over the middle of the foot. We articulate with the ground through our feet and balance is best achieved by placing the load over the middle of the foot where it wants to be anyway. Perhaps the following illustration will make clear what I am trying to say.
From Left to Right: Front squat, High-bar squat, and Low-bar squat.
Illustration from Starting Strength, 2nd ed.
The forward lean required in the low-bar style of squatting produces the greatest amount of hip flexion. This means in order to complete the rep and stand all the way up the low-bar squat will work the hip extensors and the entire posterior chain (hamstrings, glutes, adductors, and lumbar extensors) the most. The high-bar does this as well but not to the same extent as the low-bar. The posterior chain is a very important group of muscles that support good posture, powerful sprinting, and any sort of heavy lifting (note: strong hamstrings are a great support to the anterior cruciate ligament, ACL, and help prevent injury to the ACL). The posterior chain is often neglected because you cannot see those muscles in a mirror (since the general motivation for muscle development is often based on aesthetics instead of performance). On the other end of the squatting spectrum we find the front squat recruiting more of the quadriceps and less of the posterior chain. The high-bar is somewhere in between being a quad dominant squat but does not neglect the posterior chain to the same degree as the front squat does.
This is starting to sound like a low bar vs high bar post. It is not meant to be. If you want a good objective analysis of each style please read this. Let it stand that I use the low-bar style of squatting, but of greatest importance is to ensure the squat is trained 2-3 times per week.
Squatting to Depth
|Illustration taken from http://www.usapowerlifting.com/newsletter/06/novice/novice.html|
In order for you to know that your training is actually improving you need to do it the same every time. That way you know the weight you are handling is working the same muscles through the same range of motion, but with and increasing load each workout. Consider this situation: you see someone bench pressing and the first rep was all the way down to the chest and all the way back up to locked out elbows followed by a second rep that stopped short of the chest by a few inches then went back up. You'd consider the first attempt a legitimate rep and the second a mistake. That is exactly what partial or half squats are. Mistakes. The squat must be done to just below parallel every single time (the crease made in the clothing near the hip must be lower than the top of the thigh). That way comparisons between repetitions, work set weights, and lifters can be made. Partial squats do not involve hamstrings significantly but do strengthen the quadriceps. Therefore partial squats result in a muscular imbalance around the knee and are a recipe for an ACL injury. Deep squats are harder so you won't progress as fast as you might on partials. Partials lead you to believe you are strong when in reality you are not. Look at this video of me squatting just before my ankle surgery.
I remember the first set feeling really hard, and the second set was not so bad. After reviewing the video of the second set I was upset because every single rep was high. No wonder it felt easy. On the third set I tried to make sure I got deep. I didn't, except on the 4th rep during which I failed. The failed rep felt like I had 1000 pounds on my shoulders so down I went. The difference between the reps that felt hard and those that felt easy was only an inch or two. Those last few inches in the descent are critical and make a huge difference. If squatting suddenly feels easy you are probably cutting the depth a bit. Squatting correctly is hard and anything hard is usually worthwhile. Don't kid yourself by doing partials just suck it up and do the real thing.
Squatting Will Save Your Life
Squatting Will Save Your Life
As the saying goes "if you don't use it you lose it." We are an increasingly sedentary society and we need to choose to use our muscles and joints, since we don't really need to do so for survivals sake. Strengthening our bodies via low impact exercises like squatting is a surefire way to ensure that we can enjoy our golden years without a trip to the scooter store.
If you want to strengthen your knees, hips, and back (common injury sites for sedentary folks) squat deep and do it often.