To use undulating periodization (muscle confusion), change up your
 weight and rep ranges every workout. In linear periodization, stick with 
a specific rep range for several weeks and gradually increase the weight
 and decrease rep ranges. The latter has been popular among strength 15% athletes, but the muscle confusion/undulating periodization model has 
been gaining popularity thanks to a growing body of research proving 
its effectiveness. The graph shows the greater gains in muscle strength 
that trained lifters experienced while following a 12-week undulating
 program as compared to those following a linear program.