Muscle-Specific Hypertrophy: Chest, Triceps and Shoulders


Muscle-Specific Hypertrophy: Chest, Triceps and Shoulders by Menno Henselmans

Part 2: Bicep, Back and Legs

Building a massive physique, unfortunately, requires a more measured approach than simply trying to heave as much weight as humanly possible.To know how to best train a muscle, you have to first understand its physical structure, specifically its biomechanics and fiber type composition. This information helps you select the correct rep ranges, weekly volume, and rest periods for optimal results. But many lifters don’t specifically tailor these loading parameters to individual muscles. For example, they’ll dedicate 4-6 weeks to “hypertrophy” and perform every exercise in the 8-12 rep range.

That’s a mistake. Optimal hypertrophy training is muscle specific.

Muscle-Specific Hypertrophy

In this two-part article, I’ll give you all the necessary information on these two topics – biomechanics and fiber type composition – for each major muscle. Today’s article will cover the chest, triceps, and shoulders, but begin with a brief recap on muscle fibers.

Fiber One-Two-Three

There are at least three different types of muscle fiber. To increase contraction speed, increase force production, and decrease resistance to fatigue, you have type I, type IIa, and type IIb fibers. Type I fibers are slow-twitch and type II fibers are fast-twitch.

The following table lists the main characteristics of each muscle fiber type.


Each muscle has a different fiber type composition. Some muscles are fast twitch dominant while others are slow twitch dominant.

Muscle fiber type composition is largely genetically determined and has very important muscle-specific training implications. Fast twitch fibers respond best to low volume, long rest intervals, high intensity and low frequency. Slow twitch fibers, in opposition, respond best to high volume, short rest intervals, low intensity and high frequency.Perhaps most importantly, fast twitch muscle fibers have significantly greater growth potential than slow twitch fibers.

Even in untrained individuals, they’re normally more than 20% larger and it’s not uncommon for them to be over twice as large.

The fiber type composition of each muscle varies per individual, but as with most physiological characteristics, people don’t differ that much. In the general population, differences in percentage of slow twitch muscle fibers are normally above 5% and usually below 10%. So, you probably aren’t that special in this regard, even though your momma said you were.As for muscle fibers changing from one type to another, getting old seems to be a factor (the percentage of fast twitch muscle fibers in your body starts to decrease after age 30), although some studies have shown high intensity resistance training helps to prevent this.

Bodybuilding type training, with loads between 6 and 12RM, can also turn both type I and type IIb fibers into type IIa fibers.

Whatever the story, since weightlifters, powerlifters, bodybuilders, and sedentary populations differ less than 5% regarding the percentage of slow twitch fibers in their muscles, it’s unlikely that you need to take fiber conversion into account with your training. Also, the theory that high intensity (>90% of 1RM) is optimal for hypertrophy because it makes you more fast twitch and those fibers have the highest growth potential is likely false. Yes, getting stronger helps you get bigger as it enables you to put more stress on your muscles, however, it’s also important not to neglect your slow twitch fibers. In bodybuilders, equal hypertrophy of both fiber types has been found, in contrast to powerlifters and Olympic weightlifters, which show preferential hypertrophy of the type II fibers.

In conclusion, for maximum hypertrophy, you should always try to find a balance between volume and intensity.

Muscle-Specific Hypertrophy

The Test

Of course, this is all just theoretical if you don’t know the fiber type composition of your muscles.To solve this problem, some smart trainers – who for whatever reason, always seem to be French Canadian – came up with a test to find out how fast twitch a muscle is. This test is commonly known as the 80% test.In short, you find your 1RM for an exercise that targets a specific muscle and then test how many reps you can do with 80% of that. If you can do less than 8, the muscle is fast twitch dominant. If you can do more than 8, it’s slow twitch dominant.

There are much more elaborate variations of this test – for example, Charles Poliquin uses 85% for 5 reps as the norm – but the principle is always the same. If you want to know more about this test, read Christian Thibaudeau’s (amazing) Black Book of Training Secrets.

The upside of this test is that it’s individualized. The downside is that it’s impractical. I don’t know of anyone that uses it systematically because you need to find an exercise for each muscle that really isolates it, meaning it’s probably hard to do a 1RM with that particular exercise (ever do a 1RM fly?). You also can’t overcome neural factors. Bad technique or an inefficient nervous system will cause you to underestimate your 1RM and make you look more slow twitch than you really are. You can use exercises like front squats and dumbbell bench presses to get a general idea of your fiber make-up, but it’s far from perfect.

The good news is that there’s considerable research on muscle fiber type composition. Now that we’re done with the introductory notes, let’s get to the good stuff!


The pectoralis major consists of two heads – the sternal head (lower chest) and the clavicular head (the upper chest). The chest’s primary functions are transverse shoulder flexion and adduction, as in fly movements. So,

Muscle-Specific Hypertrophy

So, to target the pecs you should pick exercises that involve transverse shoulder flexion or adduction.


it’s flexion when the shoulders are internally rotated and adduction when the shoulders are externally rotated. If you have trouble seeing the rotation of your shoulder, look at your elbows when your arms are raised in front of your body. Elbows out to the side means the shoulders are internally rotated and elbows to the floor means the shoulders are externally rotated.

Remember this, because you’ll need it in a minute.

Additionally, the angle between your arms and your body determines which head of the pectoralis is trained most – incline for upper chest, and decline for lower chest.A problem many lifters have when training their pecs is that the anterior deltoid takes over. The anterior deltoid is also involved in transverse shoulder flexion, but its role in adduction is small.As such, if you want to isolate the pecs from the anterior deltoid, perform movements with the shoulderexternally rotated. The most obvious choices would be standard fly movements where you actively try to slightly supinate your hand.However, even though the pecs are best isolated by exercises involving external shoulder rotation, the pectoralis major is biomechanically more efficient and thus stronger when the shoulders are internally rotated.

This means you can’t maximally stimulate the chest without training the anterior deltoid and you should take this into account when designing a program. It’s a common mistake to overemphasize the front delts.

So which exercises are best at stimulating the chest?

For pressing movements, the more you flare your elbows out to the sides, the better.This internally rotates your shoulders and makes the exercise involve more transverse shoulder flexion and less (non-transverse) shoulder flexion, which is the movement that occurs during front raises. In agreement with Vince Gironda and TC, neck/guillotine presses are arguably the greatest pec exercise in existence. Benching like this is known to cause shoulder pain for some – not to mention decapitate the odd hapless pudknocker who erroneously assumed “Guillotine” was yet another French Canadian strength coach – so you may want to use dumbbells or not take the risk at all.

An underrated exercise that doesn’t mess up your shoulders while still really hitting the pecs is pronated grip flys. Most people do flys exclusively with a neutral grip, but the pectoralis major is stronger when the shoulders are internally rotated, so a pronated grip is superior for chest stimulation.

You can do this with dumbbells, but dumbbell flys have a resistance curve that doesn’t match the strength curve (no tension at the top) and going too deep can compromise the shoulders. As such, I prefer cables. If your gym doesn’t have attachments that allow for a pronated grip, like straight handles or short ropes, you can just grip the hooks (attachments are for pussies, right?) or pull straps through the hooks and grip the straps. As for the optimal amount of reps to use for chest exercises, use low to medium reps.

The pectoralis major is a performance muscle and both its heads are predominantly fast twitch in almost everyone, with 60% type II fibers being the average.

Take home message

  • The pectoralis major is composed of approximately 60% fast twitch fibers.
  • It’s strongest when the shoulders are internally rotated (elbows pointing away from each other during presses) and is best isolated by flaring the elbows maximally out to the sides.
  • Try medium rep flys with a pronated grip.


If you understood the section about the chest, you know why benching like most powerlifter isn’t optimal for chest development. Powerlifters often don’t have the biggest pecs, but their triceps are usually monstrous (Dave Tate, anyone?).
This isn’t only due to the biomechanics (arched back, elbows tucked, J-curve) of the powerlifting bench press that emphasizes the triceps over the chest, but also the triceps’s fiber type composition.

Even more so than the pectoralis major, the triceps brachii is a performance muscle.

Muscle-Specific Hypertrophy

It’s fast twitch fibers outnumber their sluggish counterparts two to one with approximately 67% type II fibers.

Accordingly, it’s best to use relatively low reps the majority of the time. There’s one more thing you should know about the triceps – it consists of three heads (long, lateral and medial) and the long head is biarticulate, meaning it crosses the elbow and the shoulder joint and helps to extend and adduct the shoulder (move your arm down and towards your body). That means it enters ‘active insufficiency’ when it has to function as an elbow extensor while the shoulder is adducted or extended.

That is, it can’t exert enough tension to be active at both joints at the same time. Basically all horizontal presses, including dips (you might say they’re vertical, I say who cares?) leave the long head under-stimulated. You need overhead work to train the entire tricep.

Take home message

  • The triceps is composed of 67% fast twitch fibers, so train it according to the adage, “go heavy or go home.”
  • The long head needs to be trained with overhead work.


As you probably know, there are three deltoids – the anterior, lateral, and posterior head of the shoulder.

Muscle-Specific Hypertrophy

By the way, there is no such thing as a ‘medial head.’ In anatomy, medial refers to ‘near the middle of the body,’ whereas the correct term, lateral, refers to ‘the outside of the body.

‘ The terms are commonly confused and understandably so, but they’re in fact opposites, not synonyms.Terminology isn’t the only thing that’s misunderstood about shoulder training. Many people use completely unbalanced shoulder programs. A study showed that bodybuilders have front delts that are on average five times bigger than sedentary people. But their lateral delts are just three times bigger and their rear delts a mere 10 to 15 percent bigger. (Gundill, 2002)

This isn’t surprising, given that many people do horizontal and vertical pressing on top of shoulder work – and their shoulder work isn’t balanced to begin with.

This is partly due to the misconception that side raises are a good isolation exercise for the lateral deltoid. They’re not, unless you modify the exercise. During abduction, as in a side raise, taking the force generated by the lateral deltoid as 100%, anterior deltoid force is approximately 75% and supraspinatus force is 25%. That means the supraspinatus (another rotator cuff muscle) and the anterior deltoid together produce as much force as the prime mover, the lateral deltoid.

Furthermore, these studies were done on basically sedentary people, so athletes with dominant front delts can expect even worse results. The same holds true for overhead pressing movements. Doing them behind the neck or with dumbbells helps a bit, but they still don’t produce balanced shoulder development by themselves.

So how do you train the middle shoulder without involving the front?

Decrease the amount of shoulder flexion (raising your arm as in a front raise). You may have heard that it’s safer to do side raises in the ‘scapular plane’ which is about 30° to the front, and this is correct, but that means it becomes a front raise. The same goes for not fully extending the elbow. Yes, it’s easier on the elbow joint, but you should still aim for 99% extension. This should be sufficient to keep the stress on the muscles instead of the elbow. You want the weight to be in a line that extends straight from your lateral deltoid. This means it’s better to do the exercise on an incline bench.

Try an angle between 15 and 60° incline. The lower the angle, the more you also involve the posterior deltoid.

Doing side raises on an incline brings me to another factor to increase lateral delt activity, range of motion. The first 30° or so degrees of abduction are produced primarily by the supraspinatus, after which the lateral deltoid becomes the prime mover. Now, that’s not a bad thing, because the supraspinatus needs training as well, but it does mean you need to control the motion at the top. If you’re one of those yahoos that yank the weight to the side and then duck under it, you’re just straining your supraspinatus and hardly working your lateral delts.

If you do the exercise on an incline bench, you can’t duck under it, and can focus on muscle activity instead.

There’s one more very important factor that determines shoulder muscle activity – shoulder rotation (just like with the pecs). The more you internally rotate your shoulder during shoulder flexion and abduction, the more you involve both the lateral and the posterior head, and the less you involve the anterior head. However, during horizontal shoulder abduction, as in a reverse fly, externally rotating your arm actually increases lateral deltoid activation at the expense of the posterior deltoid. So for lateral and posterior deltoid training, I advocate extending your elbow very close to fully, not using the scapular plane, and internally rotating your shoulder.

These technique adjustments increase middle delt stimulation, but also decrease subacromial space width and increase impingement risk, so take care if you have shoulder issues. Also, you can counter these problems by retracting your scapulae.

The thing is, shoulder impingement is mainly a concern if your shoulders aren’t structurally balanced to begin with and these exercises ameliorate that situation, so it’s a bit of a chicken-and-the-egg scenario. Additionally, I recommend doing shoulder isolation work on an incline, which is generally easier on the shoulder. As for the posterior delts, besides internally rotating the shoulders during reverse flys or low incline side raises, you can train them with any type of pulling motion, such as rows or face-pulls, that hyperextend the shoulder (bring the elbow behind the body). The lats and the pecs can’t extend the shoulder beyond anatomical position, so the posterior deltoids then become the prime movers. For front delts, the front raise in the scapular plane with the shoulder externally rotated is a good, risk-free front delt exercise.

Unless you’re not doing any overhead pressing work, I don’t think you need any front delt isolation work though, especially not until your shoulders are structurally balanced.

Speaking of structural balance, to train the external rotators, I recommend face-pulls with an underhand grip. Squeeze hard at the top and pull the rope all the way against your face. If you want to isolate the infraspinatus and teres minor, do side-lying external rotations. They produce the greatest EMG activity of most external rotation exercises. Remember though, reverse flys also train all the external rotators, so unless you have trouble activating the infraspinatus and the teres minor, it’s generally sufficient to just do those and face-pulls. As for reps, all scapula-humeral muscles are actively involved in maintaining posture and stabilizing the shoulder during practically every upper body movement. As such, they can be expected to have a high work capacity and are correspondingly around 60% slow-twitch dominant.

This goes for the entire shoulder girdle, with one curious exception – the infraspinatus provides some oomph for the external rotators and is fast twitch dominant by a small margin.

Take home message

  • Traditional shoulder programs emphasize the anterior deltoid at the expense of the rest of the scapula-humeral muscles.
  • Overhead presses are generally plenty of work for your anterior deltoids.
  • Add incline side raises and reverse flys with your shoulders internally rotated to balance the program and round out your delts.
  • Use medium to high reps.

I hope this article has given you some new ideas to optimize your training. In the next installment, we’ll deal with the remaining major muscles in the human body. If you have any questions or comments, leave them in the LiveSpill.

Part 2 of this article: Biceps, back and legs

About the Author

Bayesian bodybuilder, popular science author and online personal trainer, Menno Henselmans helps serious trainees attain their ideal physique using scientific and Bayesian methods. Follow him on Facebook or Twitter and check out his website for more free articles.


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