So routine is a great thing to keep you going to the gym and eating healthy. Routine turns into habit and habits are not easily broken. We normally think of habits as bad things, but there are good habits we can develop too. So why would we want to break up our routine?
Well for starters, our muscles, like anything else, get into a routine and can get stagnant, and then stop growing. So we need to break up our routine to keep them guessing if you will. By changing up our workout routine we throw our muscles into a confused state and in essence work them out more which causes the muscle fibers to stretch more, which leads to more muscle growth.
So in order to combat that plateau, change up your rep range each week. As you do change your rep range, increase or decrease your weight. For instance lets say one week you aim for 12-15 reps. The next week drop it down to 9-11, then by week three 6-8, and week four, 3-5. So your reps are decreasing each week for a 4 week cycle. Now each week the amount of weight you are lifting should increase, probably only a little bit from week one to two, but by week 4, you should be lifting a significant amount more than in week 1. Then at the end of the four weeks, repeat the process. While this is only once example of keeping your muscles guessing, you get the idea.
So break up your lifting routine. Your muscles will be glad you did.