However, I don’t come up with sources showing any hormonal measurements for different depths (and there are almost never any measurements of CNS response in any studies).

I took a look at those sources and you’re absolutely right. The definitions of full, half, and parallel squats are unclear, especially in the study using the EMG. The study didn’t even list the %’s for parallel squats without balance boards.

I found this study which compared differences muscle activation in the quads, hamstrings, and gluteus maximus at three squat depths (partial, parallel, and full). They concluded that the glutes are the only muscle that becomes more active as squat depth increases. So full depth squats do indeed activate more muscles.

http://journals.lww.com/nsca-j.....ty.14.aspx

I’ve always been interested in squats more for the claimed positive effects on GH, testosterone, IGF-1, the CNS, and other muscle building hormones and the resulting potential for increasing upper body size.

As parallel squats can be performed using a much heavier weight than full squats, I’m wondering if they would have a greater effect on hormone production than full squats even though they do not activate the glutes as much. What are your thoughts?

I can’t find any good studies comparing them. But I think there’s a good reason for that.

Let’s say you are right – there’s no real difference. I then ask, “but how do you define a half squat?” Are you thinking “half” means you go 70% down? 50%? What about if I only go 10% down – is that equal to a full squat?

No way.

That makes it hard, in a scientific setting, to define “half squat.”

But even if a study defined a half squat and found out that there was no difference, you’re still left as an individual person to figure out “how much is far enough to count as a half?”

From a practical sense, defining the target as “breaking parallel” ensures that people aren’t cheating so much that they get no benefit.