When I first started working out, I signed up for a gym that offered small-group personal training. We met three or four times a week, and the weight sessions rotated between high-rep, low-weight days; low-rep, high-weight days; and "normal" days (somewhere in the middle). The trainers would tell us that switching up the exercises like this kept our muscles from getting used to each workout, which could cause us to plateau. By "confusing" our muscles like this, we'd see steadier gains. (Related: Plateau-Busting Strategies to Start Seeing Results at the Gym)
The workout routine worked for me and set off a fitness habit that I've continued to this day. But I've always wondered about what they told me. Can we really confuse our muscles? Should we?
"A lot of the things we hear in the gym is true in regards to practical outcome, but the explanatory mechanisms are wrong," says Nick Tumminello, owner of Performance University. "So no, your muscles don't get confused. That being said, there are benefits to varying your workout routine. The more comprehensive you can make a workout, the more ways you hit your muscles, and the more likely you are to have positive benefits."
In other words, it's not necessarily that your muscles get "used to" certain exercises and they stop becoming effective. It's just that if you do the same moves, at the same intensity, and for the same number of reps day after day (or if you run the same route day after day), you're only working certain parts of your muscles. You'll see benefit from the moves, but only to a point. You'll also probably get bored. (Psst...Check out these 6 Muscle Imbalances That Cause Pain—and How to Fix Them.)
If you constantly switch it up, however, you'll be training more of your muscles. That's true whether you do the same exercises at varied intensities or different exercises altogether. "Your body is an adaptive machine. It's going to get better at handling whatever stress you put on it the more you do it. So when you stress it in different ways, you have more chances to positively adapt," Tumminello says.
In fact, he says that a recent study out of Brazil compared people who did one routine over and over, people who did the same exercises but changed their rep range, people who did different exercises for the same number of reps, and those who did different exercises and different reps. "They found that the group that kept the reps the same but changed up the exercises saw the best benefits; the runners-up were the people who changed the reps but not the exercises," he says.
So while my old gym was onto something—and you should mix up your workouts throughout the week—they may have phrased what they were doing in an overly simplistic way. You're not confusing your muscles to keep them from getting too complacent; you're challenging them in new ways at each workout to make sure they grow in a balanced, beneficial progression. As a result, you'll be less likely to plateau or get injured—perks anyone can get behind.