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.