Compound vs Isolation Exercises

A theory of muscle growth

January 10, 2020


3 min read

I use compound exercises over isolation exercises in my workouts, so I wanted to write about the trade offs. Here’s a small table comparing the difference between compound lifts and isolation lifts:

Category Compound Lifts Isolation Lifts
Joints involved Multiple Single
Muscles involved More muscles involved Fewer muscles involved
Weight More weight can be moved Less weight can be moved
Overall muscle growth More Less
Muscle growth distribution Between many muscles Focused on fewer muscles
Movement type Natural Natural and artificial
Exercise examples Squat, Bench press Leg press, Chest fly

Joints and Muscles Involved

The definition of a compound movement is that multiple joints are involved, and the definition of an isolation movement is that a single joint is involved. Since more joints are involved in compound lifts, it follows that more muscles are typically involved too.

Weight and Muscle Growth

Since more muscle is recruited for compound lifts, more total weight can be lifted. For example, you can squat significantly more weight in a rep than you can in a leg extension.

Because more muscles are involved in moving more weight, more overall muscle growth occurs, though that growth is distributed between all involved muscles.

With isolation work, specific muscles can be targeted beyond what a compound lift would target that muscle at. Because of this, smaller muscles can grow beyond what they ever could if using only compound lifts.

For example: if I do shoulder presses, a compound lift, I will target all three of my deltoids (shoulder muscles), distributing the load. If I wanted to grow my rear deltoid in a larger proportion, I could do face pulls and target just that muscle, pushing it close to its peak load. This way, I can get more growth relative to my other deltoids if I wanted to.

Because of all of these reasons, the most efficient way to build muscle is through compound lifts — you’re recruiting more muscle per repetition. People will refute this, since isolation work produces more noticeable muscle quicker. Compound lifts grow you in natural and distributed proportions, so the growth is less noticeable. It’s up to you to decide which path you’d prefer.

Natural Proportions

I have a theory that since compound movements are natural movements, their consistent use will, over time, produce the most natural and therefore aesthetically pleasing physique. You can get bigger faster if you do isolation work, but unless your work is carefully organized, you will achieve a less natural, and therefore less aesthetic, look overall.