The more weight you can squat to the correct depth, the stronger you are. It really is that simple. But when is a “squat” not a squat? When it is not below parallel – at the proper depth and therefore the proper range of motion to satisfy the purpose of the exercise. Partial squats are not squats because they do not work the maximum possible muscle mass through the longest effective range of motion, thus increasing strength.

We are not concerned with aesthetics, which focuses on hypertrophy, thin skin, low bodyfat, and pleasing proportions, most of which are genetic and outside the purview of training. Nor are we concerned with competitive powerlifting, which is unconcerned with squat depth, as YouTube will show you. We are concerned with strength, which is best produced with sets of 5 reps squatted to a position just below parallel. This is the position of maximum muscle mass involvement while generating the most force production.

Both of these factors must be considered when deciding how to best squat for strength training. The old powerlifting people got the depth correct, but the equipment manufacturers came into control of the sport many years ago, and half-squats in supportive gear sold more supportive gear.

The depth of a squat designed for a strength increase is critical, because range of motion left out of the movement cannot be strengthened by the movement, and likewise a range of motion that is anatomically inefficient at producing the most force cannot contribute to the heaviest possible efficient squat.

Heavier weights are possible with quarter squats because of the leverage advantages of more-open knee and hip angles, and the very important fact that far less work – in the Force x Distance sense – is being done. A squat that stops at 6 inches above parallel leaves out the muscle mass that operates knee extension and hip extension at lower depths.

On the other hand, nobody squats as much weight ass-to-grass as they do either high or just below parallel, because that excessive depth requires a relaxation of the quads, the glutes, and the low back in order to assume the position. Relaxed muscle is not producing force, and is therefore not getting stronger.

Another factor involved in the squat is the “stretch reflex” effect produced by the eccentrically-loaded muscle mass at the bottom of the range of motion, just below parallel. The lengthening muscle fibers under tension act as a signal for increased recruitment of more force from the now-shortening fibers acting concentrically as the squat moves back up. This is the difference between a squat paused on a box and an actual squat, with this neuromuscular “amplifier” making a big difference in the weight. The depth is a factor, because if the stretch is excessive the stretch reflex is inefficient.

And depth itself is dependent on several variables, flexibility being probably the least important. Joint angles and limb segment positions are the determining factor in depth, as illustrated by this example: if your knees continue to slide forward, is it possible to get your hips below them? No, because you can slide your knees forward to the ground in front of your toes, and your hips will obviously still be above your knees. Don't rely on your perception of knee travel to indicate depth, because it doesn't. Don't confuse bar travel with depth, because you can goodmorning the bar to below your knees with your hips far above parallel. Vertical hip travel determines depth, and that is all.

The most efficient position for depth is shins just forward of vertical, with feet at about 30 degrees out from straight-forward and thighs parallel to the feet, which requires knees to be out more than most people want them. This frees the hips to drop below the knees, produce the stretch reflex in the glutes, adductors, hamstrings, quads, and all the hip musculature, and rebound the loaded lifter back to the top. The depth is critical for a rebound, and a squat rebounding from the correct depth is actually easier than a squat cut off an inch above parallel.

Some external factors can adversely affect your depth. If you are wearing full-length sweats that do not stretch easily – or even tight shorts that resist hip flexion by grabbing your thighs – they can bind your hips and knees as you approach the actual bottom position you need. At the very least, they can give you incorrect feedback about your depth, causing you to believe that you have hit the bottom when you haven't. In the same way, a 4-inch belt can jam into the top of your thighs before you are actually deep. Most people should be wearing a 3-inch belt.

If you squat in running shoes, you are not stable against the floor, varying amounts of force get applied between varying places on your feet each rep, and depth is really hard to reach when you're trying like hell to not fall over. Get some decent lifting shoes.

So the most efficient squat for strength training must be deep enough, but not too deep. The Sweet Spot is just below parallel – the apex of the crease/fold at the hip just below the level of the top of the patella. Squatting any other way does not produce the best strength adaptation, even if it does provide a profound sense of accomplishment.

Spotting correct depth visually can be difficult. If you are standing in the wrong place, looking from the wrong angle, if the rack is in the way, if the lifter has on too many clothes, if his back is not in good extension, or if anything else interferes with your ability to accurately judge depth, you need to change something immediately so as not to lose too many reps. Move to a better point of vantage as soon as you realize you can't see the depth clearly, so your lifter can perform more of the reps correctly with your coaching.

The same rule holds for filming your own workouts: watch all your warmup sets to make sure the camera placement is optimum for the work sets. Watch the reps in slow-motion or frame-by-frame, and learn to see the knee angles and the hip angles, the back angle and back extension, and what your feet are doing during the reps (they should be doing nothing at all except nailing you to the floor). And even if you have a coach, watch them all anyway – coaches can be wrong, and it's your work and therefore your responsibility.

Learn to see correct depth when you are coaching, and especially when reviewing your own videos. Do not lie to yourself about depth, because that compromises your training and your honesty.

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