That's bullshit. The crew at Westside Barbell do box squats way more than they do regular squats, and they know how to squat.
And you obviously don't know why.
1) Training on a box will allow you to sit back onto the box to a point where your shins are past perpendicular to the floor. This places all the stress on the squatting muscles (hips, glutes, lower back and hamstrings.) When you can increase the stress on these muscles and lower the stress on the quads, then you'll be ready to see your squat poundages start moving.
2) Restoration is another major advantage of box squatting. You can train more often on a box when compared to free squatting. According to Louie Simmons, the original members of Westside Barbell in Culver City, California, used to perform box squats three times a week. Currently at Westside we train the box squat every Friday for our dynamic workout and occasionally on Monday's maximal effort workouts. If you're new to box squats, I suggest you do them once per week.
3) When performing box squats you never have to guess how low you're squatting. It'll always be the same. Think about it: when most people start adding weight to the bar, their squats get higher and higher. You see this all the time in any gym you go to. They look good with the light weights, then begin doing quarter squats when the weight gets heavy. With box squats, you'll always go low enough.
4)
The last reason to box squat is to reinforce good squat technique. Many times for the intermediate or beginning squatter, the hamstrings aren't yet developed and "sitting back" into a squat is impossible without falling over backward. To teach these athletes how to free squat properly would take months. The squat wouldn't look right until the hamstrings and glute strength increases. Why wait two or three months? Put them on the box and you'll have them squatting properly within five minutes. Within one month the hamstrings will begin to kick in because of the added stress of sitting back on the box.
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