This is another mistake I see all the time, and most lifters know better. It happens most of the time because of a weak lower back or a bad starting position. Even though your shoulders should be rounded, you must keep your lower back arched. This will keep the shin straight and the shoulders behind the bar, allowing your body to be in the proper position to pull big while keeping the back under minimal stress.
If you pull with a rounded back, the bar is going to drift forward away from the legs—putting your back in a very difficult position from which to recover. When the bar drifts forward, the weight of it will begin to work against your leverages and cause you to have a sticking point just below the knees or mid-shin level. When you pull, you can either arch your back in the beginning standing position before you crouch down to pull or once you grab the bar. Either way, it’s important to keep the lower back arched and tight.
There are many ways to strengthen the lower back for this. Good mornings, reverse hypers, and arched back good mornings are a few. You can also use a band around your traps and feet for simulated good mornings. With this technique, you only use the bands and train for higher reps (in the 20 to 30 rep range) for local muscular endurance.
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