Originally Posted by
PVC
If you're placing the bar on your back correctly and it slides down when the weights get heavy, then you're probably not keeping your chest up properly. I had this problem for weeks - in fact, it was so bad that I had to reset my squat to fix it. Chest up, back tight, and focus on doing this from the second you get under the bar to the second you rack it. It's easy to lose this tightness in between reps since you think you're "taking a break" and you slack off a bit, but you can't do that. If the bar is on your back, you have to be tight. Make sure your chest is up and your back is tight before you actually unrack the bar. Trust me, it is not easy to set your chest position correctly when you have a heavy weight on your back. It's much easier to set it up correctly before you stand up with the bar than afterwards.