The weights need to be in front of you in the beginning of the exercise, then slowly bring them back horizontally to hit your rear delts. (fitnessandpower.com)
Also, it's important to be aware that the early increase in bone density will be rapid, but improvements will taper as strength increases — bone density will not be gained at the same high rate as at the beginning of an exercise program. (tctmed.com)
Unless you are a master trainer using very heavy weights, it is neither advisable nor necessary to do one before the beginning of every exercise. (lasting-weight-loss.com)