Here’s a quote from my “Deadlift Diagnosis” article:
Rack pulls can be extremely helpful in terms of the upper back strength thickness that we desire in this instance. However, many lifters find that their carryover to improving lockout strength is minimal at best. The main problem is body position. The set-up for a rack pull doesn’t exactly replicate the joint angles that occur in mid-pull.
For instance, when I missed a third attempt at my last meet, the bar stalled an inch short of lockout. At the time, I was able to do six reps on rack pulls with 85 pounds more than that attempt. It shouldn’t have been a limiting factor, as the rack pull is done from a dead stop. Essentially, the movement winds up turning into a quarter squat rather than the completion of a deadlift, as trainees begin the movement with a near-upright torso and simply extend the knees (without much concern for the hips).
Summarily, if you’re seeing progress on your deadlift poundages from using the rack pull, it’s likely because these pulls are strengthening your upper back, not because they’re directly training the lockout (which they aren’t). In the aforementioned meet example, my upper back had plenty of strength; it was my glutes that failed me at lockout. Getting the torso out over the bar and focusing on simultaneous hip and knee extension enables you to attain greater specificity.[/quote]