BBG is right. However, your lower back can definitely me the most sore after your deadlift virginity has been taken. Its a new movement and your body isn't use to recruiting such muscle fibers. Form is important, but supplementing with lower back assistive exercises is just as important to get those erector spinae ready
Originally Posted by Bodybygamma
What part of your back is sore? If you are doing it right, your upper back should be more sore then anything else.