To unravel the relative value of compound and isolation exercises, it helps to understand what each of these terms mean. 

A compound exercise is one that involves more than two joints or muscle groups, such as the barbell squat, deadlift, or bench press. 

An isolation exercise emphasizes one joint and muscle group, such as the barbell curl (the elbow/biceps), the leg extension (the knee/quadriceps), or the back extension (the hips/spinal erectors). 

Compound exercises are fantastic for gaining muscle and strength. However, some people put them on a pedestal as all you need to fully develop every major muscle group (a group of muscles highly involved in pushing, pulling, and squatting) in your body. 

Isolation exercises, they say, may be fun, but they’re superfluous if you do enough squatting, bench pressing, deadlifting, and overhead pressing.

Who’s right? 

Can you maximize muscle growth and whole-body strength by putting your faith in compound exercises alone, or can you goose your gains by including a handful of isolation exercises in your workout routine? 

Are Isolation Exercises Useless?

You can find research to support the idea that isolation exercises are a waste of time. 

Studies conducted by scientists at the Federal University of Goiás, the University of the Amazon, Santa Cecília University, and elsewhere have found that adding isolation exercises to compound exercises didn’t significantly increase muscle growth or strength in untrained and trained men and women.

As researcher and writer Greg Nuckols has noted in an unpublished meta-analysis, though, most of these studies were conducted in such a way that made it almost impossible for isolation exercises to show benefits. 

When Nuckols analyzed the results of seven studies on this topic, he found that isolation plus compound exercises increased muscle size by about 3.8 percent versus 3 percent with just compound exercises. 

That wasn’t statistically significant (large enough to indicate a cause-effect relationship), but it would be practically significant when considered in the context of months and years of continued training. 

Think of it this way: If I told you that you could increase muscle growth by 27 percent by spending an extra 20 to 30 minutes in the gym each week doing a few relatively easy exercises, would you do it? Does Dolly Parton sleep on her back?

Basically, while isolation exercises may not drastically boost muscle growth, they do contribute in a meaningful way. And when you consider how little time and energy they require, including them in your program is a no brainer. 

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Isolation Exercise Benefits

A major reason to include isolation exercises in a strength training routine is working your muscles in several different ways—in different directions and at different angles—produces better results than just one or two ways.

In a study conducted at the University of São Paulo, for instance, researchers found that despite doing the same amount of weekly volume, people who did a combination of lower-body exercises that included the Smith machine squat, deadlift, leg press, and lunge gained more strength and experienced more balanced and proportionate muscle growth than people who only did the Smith machine squat.

The same effect has been noted in several other studies as well:

  • Researchers at Londrina State University found that training with three different exercises produced more symmetrical and complete growth of the thighs, biceps, and triceps than training with one exercise.
  • Scientists at the Federal Institute of Sudeste of Minas Gerais found that six months of bench pressing produced consistent growth of the chest muscles, but not the triceps, which plateaued after about eight weeks. This suggests that adding triceps exercises would’ve produced more triceps growth.
  • A research team at the University of Tokyo found that squats produced very little growth of the rectus femoris (a muscle in the middle of your thigh), which also suggests that including an isolation exercise that targets this muscle, like the leg extension or Bulgarian split squat, would be beneficial.

To summarize my case for doing isolation exercises:

  1. Isolation exercises allow you to continue training specific muscle groups when it’s no longer practical to do so with a compound exercise. For instance, your chest and shoulders will probably be bushed after several sets of bench and dumbbell pressing, but your triceps may be up to a few sets of an isolation exercise. Or, while your low-back and forearms are typically shagged after just a few sets of deadlifts, your lats and hamstrings aren’t. 
  2. Isolation exercises allow you to train a muscle group in different positions and through different ranges of motions, which likely improves muscle growth. For example, bench pressing and overhead pressing (compound exercises) train your triceps in a very different position than triceps extensions or dumbbell pullovers (isolation exercises). 
  3. Doing the same three or four exercises every week for months on end gets boring, and boring workouts tend to be less productive than engaging ones. 
  4. Repeating the same exercises in the same way for long periods of time probably increases the risk of repetitive stress injuries (a gradual buildup of damage to tissues from repetitive motions), especially when you start using heavier weights. 

While the lion’s share of your gains will come from compound exercises, by supplementing them with the right isolation exercises (like I recommend in my books for men and women, Bigger Leaner Stronger and Thinner Leaner Stronger), you’ll get even more muscle and strength out of your training.

Isolation exercises come with their own quirks and challenges, though, and one of the main ones is that it’s difficult to keep adding weight over time. 

In other words, you’ll plateau much sooner on most isolation exercises than you will on most compound exercises. If you’d like to learn how to counter this problem, check out this article on the 8 best ways to progress on isolation exercises. 

+ Scientific References