I don't know. A pre-existing back injury? Does it still tingle?
As a little background: I have been lifting off and on for a few years, with periods of serious dedication and periods where I just do maintenance work. I have been doing squats and deadlifts for a while, although my form has probably not been ideal. I recently read Starting Strength and adjusted my form as a result. Previously I had been doing a high bar squat more akin to an olympic style. However on my first workout with the form described in the book I felt a strange tingling in my right lower leg and foot on the ascent of my squat. The weight used was pretty light, (only 155) and less than I have used in the past. What could have caused the sensation?
I don't know. A pre-existing back injury? Does it still tingle?
Hyperextending his lower back as part of the set-up (instead of lifting the pelvis)?
Why that assumption?
Personal experience, although from a different lift - I had ruptured L4/L5 and L5/S1 on the posterior side after carelessly picking up a bar I had partially unloaded. To this day, if I hyperextend my low back, I can induce tingling in my right leg when I have weight on my back (either in a squat, at the top of a deadlift, or when pressing).
The pelvic lock-out that you showed us at the seminar has eliminated this.
So what I'm getting at is possibly old injury that's being aggravated by mistaking low back hyperextension for lifting the pelvis, as I was doing.
I have never had any back pain or problems prior to the workout. The tingling only lasted a second or two on the ascent and quickly dissipated. Could it have something to do with breathing, or lack thereof?
Why breathing?
Maybe not so much breathing as core stability. On the third set I made sure to take a breath after every rep and it seemed to help. I squatted again today and didn't notice anything.
@tertius
Sounds plausible. Maybe I just need to work on bar placement.
It wouldn't have anything to do with the bar, as the bar is way, way too high up the back to be influencing the nerves that feed your legs (aside from creating a load, of course). All those nerves enter your spine in the lumbar area. So, if it was a nerve thing, you'd have to be doing something in your low back to cause the pressure change. A slight shift in position or tendency to change your spinal extension, something like that. I bet after you've done low bar a bit longer, it stops happening, if that's what it is.