Periodized training programs, in which the weight used is systematically increased while reps decrease, have been shown to be very effective for producing gains in muscle strength and size. The most popular form, linear periodization, involves increasing the weight every 4 weeks or so and has proven to produce impressive strength gains. Undulating periodization is a form that involves changing up the weight and rep ranges every time you train a muscle group, using no set pattern for increasing or decreasing weight. Few studies have compared periodization techniques for muscle growth, but we believe that the muscle confusion that comes with undulating periodization will produce greater gains in muscle size.
Researchers in Brazil had untrained men follow a linear periodized weight-training program for 12 weeks or an undulating periodized program. The linear periodized group did two set of 12–15 reps per exercise for the first four weeks, then 3 sets of 8–10 reps per exercises for the next four weeks, and 4 sets of 3–5 reps per exercise in the final four weeks of the study. The undulating group used those same three set and rep ranges but cycled them each time they trained.
While the group following the undulating plan increased triceps size by about 5%, the linear group saw no such increase. The undulating group also increased their biceps size by 10%; the linear group only increased their biceps size by 5%. The undulating group also increased their bench press strength by more than 25%; the linear group only increased by 10%.
Undulating periodization where weights and rep ranges change frequently, but not in a specific pattern, are superior to linear periodized programs that hold each rep range for four weeks. This is not surprising as maintaining one rep range for four weeks may help you build strength in that particular rep range, but you may lose some of the benefits you gained from the previous rep ranges. With the undulating plan, you cycle so frequently through the rep ranges that you get the benefits of each rep range without losing the benefits you gain from the other rep ranges.
Although the researchers changed the rep ranges in the undulating group every time they trained, they were using a full-body workout that trained all major muscle groups in one workout. Since most bodybuilders use a weekly training split that takes 4–5 workouts to train the entire body, you should change the rep range only after cycling through all workouts. This study only used three rep ranges, but we suggest you try at use at least 4 rep ranges, such as 12–15, 9–11, 6–8, and 3–5. A sample 12-week plan for someone who trains each muscle group once per week can be found in the chart above.
Reference: R. Simão et al., J Strength Cond Res., 26(5):1389–95; 2012.