Should pull-ups (for the shoulders and upper back) and chin-ups (for the biceps/forearms) be done every day or every other day? Also, should they be done at the same time, (do a few sets of chin-ups, then do a few sets of pull-ups, or do a set of pull-ups and then a set of chin-ups, and keep rotating back and forth?) Or should they be be done on a different day?