You all aren't stretching properly. Try this-- lay on your back, take your right leg and bend it a 90 degree angle. Take your left leg and bend it across your right thigh. Pull your right leg toward your chest and you'll feel a nice stretch in your hip flexors. A lot of what you guys are experiencing is sciatic nerve pain. Doing this stretch before and after back/leg workouts will SIGNIFICANTLY decrease the chance of injury.
I DL 450+ with regularity.