First, I’ll put out there that I tried hook grip and I hate it, so it’s mixed grip for me.
Heavy working sets always seem to windmill a little, especially as I continue in reps, but today was a test day and my new PR involved horrendous windmilling, hence my being motivated to ask what I should be doing to fix it. My elbow did seem to be locked out, which was a problem I seem to have fixed.
Edit: As an aside, the buddy I got into barbell training last summer has gone from never doing Squats or Deadlifts to doing 3x5 for 315 this week, and he pulled 440 today.
I too have had to work on this when using mixed grip. I try and focus on “weight back, tight lats” moreso when using mixed grip. I have found for me that the bar stays on the legs better when using regular grip, but have to work on it more when using mixed grip.
I keep working on hook grip but man my thumbs are screaming after sets.
The first thing that jumped out to me was for you contract the lats hard and keep them contracted to keep the bar on the legs on the way up. So yeah, what Sean said.