Make sure you use the valsalva maneuver. Take a deep breath and hold it while flexing the abs (when using a belt, push your stomach OUT against the belt - many dont use the belt correctly). This is VERY important so as not to strain the back. In addition, the technique will strengthen the core because it will keep the lower back and abdominals rigid.
Another piece of advice in addition to Beefcakes reponse: Do not let your hips rise faster than the rest of your body. Worst case scenerio - your legs are straight yet your back is bent, struggling to lift the weight...suddenly, one of your lower back discs falls out onto the floor (DON"T lift heavy until your back remains straight!!!).
ONE MORE: When performing sets with more reps than 3-4 don't use a belt. It is not necessary because you will strengthen your core not using one. If you are using correct form, you will not pull anything. In another sense, whats the point of being able to deadlidt 700 pounds when your core is too weak to dead 350 without a belt? DOESNT make sense. Use a belt during low reps 1-4, so you don't strain yourself during max testing.
__________________ "Before I'd get in the ring, I'd have already won or lost it on the road. The real part is won or lost somewhere far away from witnesses - behind the lines, in the gym and out there on the road, long before I dance under those lights." -- Muhammad Ali |