What's up guys! Michael Kamalu here aka Dr Gaines and, in this video, I'm going to go
over everything you need to know about shoulder anatomy and physiology in order to maximise the
effectiveness of your workouts. Now, since there's a lot of material to cover here, and I want to do
it all justice, I'm actually going to split this up into two videos. In the first video,
part one, I'm going to go over the shoulder joint as a whole, including all of the muscles
that go into its movement. Hint! There's a lot more than just the Deltoids. Then, in part two,
I'll go over the Deltoids specifically, and a deep dive into the three different heads
of the Deltoids and how you can work out each one of them. So, first we need to understand a
little bit about the joint itself. The shoulder is actually called the Glenohumeral joint. It's
called that because the Humerus comes into contact with the Glenoid Fossa, which is that concave
shaped edge of the scapula. Fist is the head of the Humerus and my hand is the Glenoid Fossa,
so the shoulder moves around inside that joint. The Glenohumeral joint is the most complex joint
in the human body. It also allows for more mobility than any other joint. But, in anatomy,
mobility comes at a price and that is stability. In other words, the more movement a joint has,
the greater chances are that something is going to go wrong and that's part of the reason why
the shoulder is the most commonly injured joint for weight lifters and athletes. There's another
big reason for that and I go in detail over it in another video that I will link below.
What we're going to focus on is understanding all of the muscles in the shoulder and there
are 17. 17 different muscles that cross the Glenohumeral joint and therefore, when activated,
move your shoulder to one degree or another. Some of you may be thinking "Man, I don't care
about all the other muscles. I just want to work my Deltoids." However, if you really want to hit
your Deltoids and maximise the efficiency of your Deltoid workouts, it is imperative to understand
the other muscles that move the shoulder for multiple reasons. A big one is that, if you know
what other movements the muscles do, then you can isolate them and keep them from contributing
to lifting the weight when you're working your Deltoids so you can isolate it much better and put
a lot more load on the Deltoids themselves. For example, there are many lists that people do where
they think they're working their Deltoids, but in reality, they're really activating, mostly, their
Trapezius, Pec Major or the Coracobrachialis. Obviously, in those situations, you're going
to be leaving results on the table. You're not going to get the same workout on your Deltoids
that you'd otherwise could. Now, we're going to go over those 17 muscles one by one and I'm going
to break it down by movement. So, we will start with what muscles do flexion of the shoulder.
Inflection is moving your arm out and up in front of you and, remember as we go over these muscles,
we're excluding the Deltoids. For now, just forget about them. I'm only going to be talking
about the other muscles that do those movements. Muscle number one that flexes the shoulder is the
Coracobrachialis. It is a relatively small, but powerful muscle that originates here,
on this bony process of the Scapula called the Coracoid process and inserts down here,
on the front of the Humerus. Now, I know it's probably hard to see that and so, that's why
I've also included the images on my left here so that you can see those in better detail.
As a quick side note, you'll see me talk a lot about origination points and insertion points.
Why are those so important to understand? Well, in order to know what any muscle does and,
therefore how to most efficiently work out that muscle. You have to know where it originates
from and where it inserts because that will tell you what that muscle does. For example,
because the Coracobrachialis originates here on the Scapula, and inserts on the front of the
Humerus. What's it going to do when it contracts? Well, it's going to bring that up closer to the
origination point. The insertion point will become closer to the origination point and, in this case,
it flexes the upper arm up. There are two more muscles that do flexion of the shoulder. The
second is the biceps. Now, most people understand that the biceps flexes the arm at the elbow
but, most do not know that it also flexes the arm at the shoulder. And the reason is, because of
again those origination and insertion points. The word biceps has BI in it because it has two parts.
As you can see, they both have the same insertion point just past the elbow on, what's called the
radial Tuberosity. But, as you can see, they have very different origination points. So, right now,
we're focused on the long head of the biceps, which is the most lateral one. Curls up around the
head of the Humerus and originates from a point on the scapula called the Supraglenoid Tubercle
super. Meaning, on top of the Glenoid and Tubercle, just refers to ridges on the bones that
stand out. So, when the Long Head of the biceps contracts, not only will it pull up on the Radius
bending the elbow, but it will also pull from its origination point up here on the Scapula and flex
the arm at the shoulder. As another side note of why it's so important to understand anatomy,
that actually means that you don't get a full contraction on your biceps unless your arm is
flexed up at the shoulder. The third muscle that flexes the shoulder is the Pectoralis Major.
Now, as you can see, it inserts on what's called the Greater Tubercle of the Humerus
aka big bony part on the arm. However, there's not just one origination point. Tech Major is so large
that it has multiple different origination points and, therefore, has multiple different actions
because of that Pec Major is broken up into three different functional parts. The Clavicular part,
the Sternal part and the Costal part. So, which part of the pec is going to flex the shoulder?
Well, that means the fibers have to be pulling the Humerus up, so it is the clavicular fibers of Pec
Major and called Clavicular because they originate from the Clavicle or the Collarbone. Then they
insert there, like all of them do, on the Humerus. So, when those contract, it's going to pull your
upper arm up and flex the shoulder activation of those sternal fibers. It's going to adduct your
arm, or bring it closer to your body and it's also going to medially rotate your arm. As you can see,
since the costal fibers are below the insertion point. They're going to pull down on the shoulder.
That's actually why decline presses work your lower chest. I'll link another video below where
I actually go over the Pec Major in a lot more detail and the 10 ways to work it, so that covers
flexion of the shoulder. And now, we're going to move into abduction which is moving your upper arm
away from your body to the side that brings us to muscle number four and that is the Supraspinatus.
The Supraspinatus originates on what's called the Supraspinous Fossa of the scapula. Fossa
generally means a hole or valley type of landmark. And so again, I know this may be hard to see
but, the top of your scapula, all along that border there is where it originates from and
then it will go under this top part of the scapula which is called the Acromion and insert on the
head of the Humerus. Specifically the greater Tubercle of the Humerus aka the big bony part. So,
what's going to happen when the Supraspinatus is activated and those fibers contract
or it's going to pull on the head of the humerus and abduct the arm? So, what's really important
to understand here is, there are multiple studies that show that the Supraspinatus is exclusively
the muscle in charge of the first 15 to 20 degrees of abduction. So, the Deltoid does not even get
activated until after your arm is about here. I'll go into that more detail in part two of this
video. The next muscle that abducts the arm at the shoulder is one that you probably wouldn't have
guessed. But, is the Serratus Anterior, that's that finger muscle that lies along your ribs here.
Specifically ribs one through nine are where it originates from and then it travels under the
scapula and insert on the back side of the Medial Border of the scapula. So, what's going to happen
when it contracts? Well, it's going to pull the Scapula closer to your body and that, inevitably,
ends up abducting your arm. The last muscle we'll go over that does abduction of the shoulder
is actually the Short Head of the biceps. But it's only true if your arm is rotated backwards and to
your side, as we already went over. Both of the biceps insert down here on the Radial Tuberosity,
but the Short Head originates from this Coracoid process. So, if your arm is rotated out,
then it is one of the primary muscles that will be activated in order to pull the Humerus closer
to the Scapula and abduct the arm. It also does give some activation with flexion of the shoulder
but is a minor player there. However, again, when rotated out it becomes a major player
in abduction. That's a great example of how very small variations in movements positions
resistance angles of your body can have a drastic impact on how much each muscle gets activated,
how much you're working them next. We will go over extension of the shoulder. If flexion is
moving the arm out and up, then extension which is the opposite, is moving your arm back. Even
hyper-extending your arm which is bringing it behind your back. The first extensor we'll discuss
is the Latissimus Dorsi, most commonly called the Lats. It originates from the spine specifically t7
to t12 of your Vertebrae and travels up to insert on the Lesser Tubercle of the Humerus or the
smaller bony point. So, when the shoulder is in a flexed position, it's stretching the lats and then
it is the Lats along with a couple other muscles that will pull it back down. Or extend the arm at
the shoulder and it also does some Hyperextension of the shoulder but it's not a major player. What
is a major player in Hyperextension is the next muscle and that is the Teres Major. The Teres
Major originates on the Inferior angle of the Scapula the bottom and then inserts similarly on
the back of the Humerus, specifically the Lesser Tubercle of the Humerus, the smaller
knob. So just like the Lats. When the shoulder is flexed, it extends it and is a major player in
Hyperextension of the shoulder. The other player in extension and Hyperextension of the shoulder,
you may not have guessed but, it is the Triceps. The Long Head of the Tricep specifically is the
only of the three heads that does not originate on the Humerus. The other two originate on
the Humerus and insert down here on this bony part of the Ulna, called the Olecranon and so,
when activated, extend the elbow joint. However, the Long Head of the Triceps originates up here
on the Scapula, specifically the Infraglenoid Tubercle of the Scapula and fro below the Glenoid
Tubercle little knob. So, what's going to happen when the Long Head of the Triceps is activated?
Well it's going to pull the Ulna closer to the Inflammatory Tubercle of the Scapula.
Another example of the importance of anatomy that means that you do not get a full contraction
of the Triceps or the Long Head of the Triceps, at least unless the arm is bent in a hyper extended
position, and I do another video on that which, again I will link below. That brings us to our
next motion, which is elevation of the shoulder or bringing your shoulder up. There are two primary
muscles involved in elevation of the shoulder. The first is the Trapezius. Trapezius is one of
the largest muscles in your body and expands virtually the entire back and, similarly to
Pec Major is due to that it's broken up into three different functional parts. The Descending Head,
the Transverse Head and the Ascending Head of the Trapezius. So, what part is going to elevate
the shoulder? Well, the ones that are above the shoulder, so the descending part of the Trapezius
originates from the back of the skull as well as some of the Cervical Vertebrae
and then travel down and insert all along the spine of the Scapula, which is this
bony part sticking out on the back of your shoulder. So, when those contract, it's going
to bring the spine of the shoulder closer to the head. Now, that's important to understand because,
when people say they're going to do shoulder shrugs, well they're actually not working their
Deltoids at all. There's the Trapezius and one other muscle that is primarily responsible for
that. The other muscle is the Levator Scapula. You can guess what it does just by the name
Levate Elevate Scapula. So, it originates from the c1 and c2 Cervical Vertebrae, specifically the
transverse processes which are the ends that stick out to the sides and inserts on the Acromion,
which is the lateral most part of your Scapula. Most people can feel it in their shoulder.
So again, when it contracts, it pulls the shoulder closer to the bottom of your Head. The next motion
is retraction attraction, bringing your shoulder back behind your body. I won't take a whole lot
of time on this one because it's the muscles of the back that are responsible. Most people
aren't trying to work their shoulder when they do back workouts. However, for sake of completion,
there's the Rhomboids. Rhomboid Major and Rhomboid Minor, which originate along the spine
and insert mostly along the Medial Border of the Scapula, therefore bringing your shoulder back
behind your body. Then there is the Acromial section of the Trapezius that we went over
earlier the next movement is protraction of your shoulder, which is the opposite of retraction.
Protraction. Protraction is a very common movement in people working their shoulders. There are two
primary muscles responsible for protraction. The first is the Serratus Anterior which we already
went over because it originates from the front of the ribs and then inserts back behind the Scapula
along the Medial border. It's going to pull that shoulder girdle tight against the body.
The other muscle that protracts the shoulder is actually Pectoralis Minor which originates on
the medial ends of the ribs, specifically ribs three through five. But, unlike Peg Major,
it does not insert on the Humerus. Pep Minor actually inserts on the coracoid process.
Now, we've gone over a few muscles that insert there but, you can see how, when it brings the
insertion point closer to the origination point, it's going to protract your shoulder.
And there's another movement it does and, because it's pulling from beneath the coracoid process,
it also depresses the shoulder brings it down. The final two motions we're going to hit are internal
and external rotation of the shoulder. A lot of people think that, when they grab a cable or
worse a free weight and do internal and external rotation, that they're working their Deltoids.
In reality, there's very minimal activation of the Deltoids. We'll start with external
rotation and that brings us to the Infraspinatus Infra below Spinatus spine. So, the Infraspinatus
is right below the spine of the Scapula and originates from what's called the Infraspinous
Fossa, the valley landmark that lies below the spine and then comes across and inserts on the
greater Tubercle of the Humerus. So, you can see that, when it's activated it's going to pull this
greater Tubercle of the Humerus which is, right now facing laterally. It's going to twist it,
bones here can't really do that movement but it's going to externally rotate the shoulder. The other
muscle that externally rotates the shoulder is the Teres Minor. We already went over the Telly's
Major but, the Minor originates along the lateral border of the Scapula. Then also inserts on
that greater Tubercle of the Humerus. Again, when that contracts, it's going to externally rotate
the shoulder. The antagonist for these two muscles and the muscle that does internal
rotation of the shoulder is a muscle called the Subscapularis. Sub being under or behind scapula,
it actually originates from the back side or underside of the scapula and then travels around
to insert on the front of the Humerus in what's called the Lesser Tubercle or the smaller knob
and so, when that contracts, it's going to bring that front of the Humerus closer to the back side
of your scapula. The result is internally rotating your arm. Now, if you remember, I did mention one
other muscle that also does medial rotation of the shoulder and that is Pec Major. So,
if you have a cable and you're doing internal rotation, you're not touching the Deltoid
at all but, it actually can be a pretty great finisher or a superset for working your chest.
And there you have it, those are the 17 muscles, besides the Deltoid, that move the shoulder joint.
As you can see, I wasn't kidding when I said it's the most complex joint in the body and, we really
just brushed the surface. But that's why, when a client tells me they want to work their shoulders,
I'll ask them to be a little more specific. It also emphasizes how important it is for anyone
who wants to get serious about weightlifting or fitness to understand the anatomy of their body,
before they go around throwing weights. Because, again, very slight variations in position motion
resistance angle can have drastic impacts on how much you are working each muscle and,
not to mention, can have a dramatic impact on preventing or rehabbing injuries. So, now that
we understand the shoulder as a whole, ready to go into more detail on the muscles that most people
are referring to when they say they want to work their shoulders and, that's the Deltoids. So,
stay tuned for part two. I'll be releasing that within the next few days. If you like
these videos, make sure to subscribe and turn on those notifications and we'll see you then!