How often should I switch up my exercise routine?

If you’ve spent any appreciable amount of time in the fitness space on social media, you may have come across the term “muscle confusion” — the idea that workouts should be constantly varied in order to provide a novel stimulus and enhance muscular adaptations. Does the science back this idea up?

In an 8-week study that had resistance-trained men perform workouts composed of unilateral leg presses and leg extensions,^[1] one leg was randomly assigned to perform the same workout each session, while the other leg cycled through 4 different workouts that varied in (i) the number of repetitions performed per set, (ii) the number of sets performed, (iii) the type of contraction (i.e., only eccentric contractions were performed), and (iv) the amount of rest taken between sets.

It was found that muscle gain did not differ between interventions. Furthermore, intraindividual analysis indicated that none of the participants experienced greater muscle growth from one intervention than the other.

This suggests that frequent variation does not enhance muscle gain. However, as noted in the response to the question of, “Are a variety of exercises necessary to maximize muscle gain?” there is indeed a benefit to including a variety of exercises within a training program. In the aforementioned study, the exercises performed remained constant, while other variables were manipulated. Does frequent variation in exercise selection affect muscle gain?

There is very little research examining this question. In the best study currently available, resistance-trained men were randomly assigned to one of two 8-week resistance exercise programs. The control program featured upper-body and lower-body workouts consisting of the same exercises each workout, and the interventional program featured upper-body and lower-body workouts consisting of exercises randomly selected from a database of 80 different exercises each workout.^[2]

In the end, there were no significant differences between groups for changes in muscle thickness of the individual quadriceps’ muscles. However, it’s worth highlighting that there was a large increase in intrinsic motivation in the group that varied their exercise selection, while there was a nonsignificant decrease in the group that kept exercise constant, which may be important for long-term adherence.

While the results suggest that frequent variation in exercise selection does not affect muscle gain, this was a single 8-week study. Over the longer term, however, there may be disadvantages to overdoing the variation. It’s possible that too-frequent variation in exercise selection could impair muscle gain by increasing the difficulty of achieving and quantifying progressive overload (i.e., the gradual increase in stress which, when imposed on the body, facilitates continued adaptations)^[3] — the primary stimulus for muscle gain. Also, rotating exercises too frequently may cause excessive fatigue because an unaccustomed stimulus promotes muscle damage.^[4] This could lead to a subsequent reduction in training volume and frequency, and thus an impairment in muscle gain.^[3]

With respect to strength, the story is a bit different. Given the important role of the specificity principle in strength gain,^[5][6] it follows that to maximally increase strength for a given exercise, that exercise should be emphasized in the training program and performed in a manner that facilitates improvements in the strength test of interest. For example, in a study that had one group train with a load corresponding to a 3–5 repetition maximum (RM) and another group train with a load corresponding to 20–28RM, the former experienced greater increases in 1RM strength, while the latter performed better on a test of repetitions to failure at 60% of 1RM.^[7]

Further evidence for this stems from the study mentioned above.^[2] It was found that absolute changes in 1-repetition maximum bench press strength favored the control group (4.7% vs. 0.77%), which regularly included the bench press in their upper body workouts, while the exercise variation group performed the bench press much less frequently (exactly how much was not specified) due to the nature of their program.