One reason why many people struggle to perfect their deadlift form is the fact that they don't maintain tightness in their upper back. Think of the upper back as being the "foundation" for your arms during the deadlift. Since your arms are attached to the bar, having a weak foundation is simply asking for trouble.
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With this in mind, think about placing your shoulder blades in your back pocket. This causes scapular retraction and downward rotation plus helps maintain shoulder extension. This cue helps engage virtually all of the muscles in the upper back and can make the difference between a glorious
PR and a miserable fail.