Training a Muscle’s Fiber Makeup for Maximum Size

Q: I am a newbie to bodybuilding. How heavy should I go on shoulder exercises to get a full workout? I am already in good shape from athletics.

– Ian E.

My Answer: If you’re going to be a bodybuilder, then what you’ll need to do is focus on “size training” as opposed to athletic training.  Depending on the sport your athletic background should have helped developed the strength, explosive and endurance of your deltoids.

Each muscle group has a “personality” based on its fiber makeup.  This means that the deltoids respond to a specific range of repetitions and a specific tempo.  In fact the 3 deltoid heads differ from each other in terms of rep ranges.

The anterior delts are comprised of primarily fast-twitch muscle fiber, so they respond best to low reps and extremely heavy weight.  If you look at weightlifters, they have well developed delts from explosive overhead lifts like the clean and jerk.

The lateral (sometimes called medial) delts are composed of strength endurance fibers, so they respond best to high reps.  This is why basketball players have full but ripped delts, because they’re constantly raising their arms overhead.

I go over these differences between the deltoid heads in Strength and Physique: High Tension Exercises for Muscular Growth. If you understand the differences in fiber makeup between the different muscle, then you can train them accordingly for maximum hypertrophy.


Q: Are “muscle density” routines/training a scam? Isn’t diet & cardio going to get you to a place where your muscle looks “hard and full, with paper-skin”? Or, is there actually some substance to the info out there?

Thank you for your time.



My Answer: Well I don’t know what sort of training routines you’re looking at, but different types of training can get your muscles more “dense.” What do we mean by muscle density?

Muscle density refers to how thick and hard the muscles look and feel. This is different from “training density,” where you do more work per unit of time. Muscle density is developed through sarcomere hypertrophy. In other words, the muscle fibers grow by thickening in diameter. This is different from sarcoplasmic hypertrophy where your muscles grow from increased fluid retention.

How do you develop sarcomere hypertrophy? Heavy weight and low reps. Anywhere from 3-8 reps, with a target rep range of 4-6 reps being ideal.

So cardio is not the way to go if you want muscular density. If anything, you will lose muscular density, because cardio is based on low weight (or more accurately, low force production) and ultra high reps, the exact opposite training method.

But if you want paper thin skin, then diet plays a crucial role. A cyclical ketogenic diet as mentioned in Training for the Busy Bodybuilder is the way to go.


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