When weight training, you want to be particularly aware of your posture. Keeping your head, ribcage, and pelvis in the proper position (with your core tight) will improve your performance and reduce the risk of injury. Keeping this position may require you to lower the loads (decrease weight) on each of your exercises. If you are unable to find this proper position, talk to your trainer. You may need additional mobility or flexibility training.
Patrick Minassian is a Personal Trainer at Body & Soul