Some people are just built different and I mean
that literally. Anatomists have long known that
you never quite know what you're going to find
during human dissection and I could tell you
from personal experience it's pretty exciting
to find something unexpected and the reason this
happens at all is because human beings, like
all other biological organisms, are subject
to variation within our species. Nature is
constantly experimenting to see if subtle
variations will equate to greater reproductive
or environmental success and in today's video,
with the help of the cadavers here in the lab,
we're going to take a look at a few different
musculoskeletal variations and see if they
can actually make someone better equipped at
certain activities including athletic performance.
It's going to be an unusual one. Let's do this.
[Intro]
Take a moment and ask yourself, what is normal?
How do we arrive at the conclusion that
something is just as we expect it to be or
not at all like we expect it to be? Now,
this question isn't unique to anatomist
by any means but it's something anatomist
have struggled with for a very long time.
When you dissect enough human beings, you're
going to find all sorts of blood vessels,
nerves, muscles, and even organs doing some
pretty unexpected things. Maybe they take
a different pathway than you're used to or
maybe they're just in a completely different
position than you anticipate such as in Situs
Inversus which is where the internal organs
of the body are completely reversed. The heart
projects to the right. The liver's on the left.
The stomach's on the right. Everything's
backwards yet still functional and look,
I get it, in Situs Inversus is extremely
rare but I think you get the point here.
Often times, there's a really fine line between
normal and abnormal. What could be considered
normal for one population might be considered
abnormal in a completely separate population. An
easy example would be height. The average height
for males in the United States is 1.77 meters or
5 foot 9 inches while the average height for a
male in India is 1.66 meters or 5 foot 5 inches.
Now it's not as though one is normal and the
other isn't. This is just a very obvious example
of variation within the species. But let's focus
on some less obvious ones. But real quick I want
to thank the sponsor of today's video Yogabody
Teachers College. When this lab first opened,
we exclusively taught in-person labs to
a variety of students: EMTs, paramedics,
medical assistants, massage therapists, and even
those going through yoga teaching certification
programs and I remember being very surprised
at just how much yoga teachers actually know
about the human body, which is one reason I'm
so impressed with Yogabody Teachers College.
They specialize in science-based online
certification programs for yoga teachers,
yoga breathing coaches, yoga trapeze teachers,
and stretching coaches. If you're interested
in starting a new career or side job helping
people improve their health, overcome injuries,
manage stress, or just live their best lives
longer, Yogabody's courses might be right for you.
They take a science-based business positive
approach to yoga, helping turn passionate students
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Since 2007, Yogabody has certified over
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They're backed by Yoga Alliance,
American Council on Exercise, and
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entire world eligible for college credits.
They prepared a free report for you called How to
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can just click the link in the description below.
Biceps brachii is perhaps the most
famous muscle in the human body. Now,
its name actually translates to two-headed
muscle of the brachium which is a really
good name considering that's exactly
what it does for most people. Typically,
the long head of biceps brachii originates
at the supra glenoid tubicle of the scapula
while the short head originates at
the coracoid process of the scapula.
Both heads will then insert at the
radial tuberosity of the radius. However,
multiple cadaver based studies have shown that it
can have anywhere between three and seven heads.
Sometimes attaching in the same locations
that the other two heads attaching or
it can get creative and attached
elsewhere on the humerus or scapula.
Most often, a third head will arise between
the long and the short heads and will attach
near the insertion of another famous muscle
called pectoralis major. Now studies haven't
really determined any usefulness for the super
numeray heads at this point but that doesn't
mean there isn't any usefulness. It just means
at least we haven't tested it all that much.
I mean, any additional heads means you're going
to have tension being transmitted differently
through the muscle and throughout the skeletal
attachments. In preparation for this video,
I looked for examples of body builders that
had additional biceps heads and honestly,
I didn't really find anything and it's possible
that I just didn't really look hard enough but
given that the incidence rate is around 13%
or less of the population actually has super
numerary biceps heads, it's not all that
surprising that I didn't find anything.
However, there's another variability within
biceps brachii eye that is all over the place and
there's even a test that you can perform yourself
although the test is far from scientific. Look,
muscles can be divided into what are
known as muscle bellies and muscle tendons.
Based on your genetics, you're going
to have a specific muscle to tendon ratio.
For some, the muscle belly is long, giving
the appearance of nice, full biceps brachii,
but for others, the muscle belly is much
shorter making the muscle belly bulge more
giving it a characteristic peak. Now, bone
length can also determine or help determine
the appearance of your biceps but the test
you'll commonly see be performed by people
is called the Finger Test. And what they'll do
so you'll bring your arm up and - I want you
to know I have impressively unimpressive
biceps and also I'm wearing a sweatshirt
here but if you take a finger and what you're
trying to do is you put it between your elbow
and then the muscle belly. So, you might
be able to fit one finger, two fingers,
three fingers and that will help you determine
your muscle to tendon ratio but at the end of
the day, it really doesn't matter all
that much which you have because you
can still grow the biceps regardless but it
definitely is going to affect its appearance.
Another famous muscle called the rectus abdominis
typically presents with eight individual segments
which are created by three horizontally oriented
tendonous intersections. The muscle originates on
what's known as the pubic crest of the pubic
bone and then travels and inserts up at the
xiphoid process of the sternum as well as the
costal cartilages of ribs five, six, and seven.
When the muscle contracts, each of those
individual segments will bulge and then
when you add that all together, you get a
ratcheting effect or more appropriately is that
crunch appearance that we're all familiar with.
However, some individuals can have up to five
tenderness intersections giving them 12 individual
segments or a 12 pack. A 10 pack which is created
by four tenderness intersections is far more
common than a 12 pack but still very uncommon.
It's possible that somewhere around 20% or so
of the population has a 10 pack while only one
to 2% of the population has a 12 pack. Now,
it's important to know that these percentages
are extrapolations based on the available
data, so please take them with a pretty big
grain of salt but you're probably wondering
does having these extra segments give you any
kind of advantage over those who have less
segments and the answer is... Probably not.
Don't get me wrong, it looks awesome for sure and functionally,
the increased segments might allow for some
more precision during contraction but the
problem here is a limit in range of motion by
the skeleton. You see, the ribs physically get
in the way and then the facet joints which
run up and down your vertebral column,
they define the allowed range of motion
throughout your entire vertebral column.
So, it's not as though just because you
added more segments, you can bypass the
skeletal limitations. However, if you're
a body builder, then it most definitely
comes with an advantage because again, it just
looks awesome. I can actually continue to give
example after example of variability within
specific muscles but instead, I now want to
focus on variability and how skeletal muscle
actually attaches to the physical skeleton.
For the nerds out there, this is
going to be a real treat because
we're about to get into the weeds
but it is very very cool. You see,
the real name for muscle attachment sites is
Enthesis and there are two different types of
enthesis. You have a Fibrous Enthesis
and a Fibrocartilaginous Enthesis.
You see, muscles are completely enveloped in connective tissue.
It surrounds every single muscle cell,
groups of cells, and even the entirety
of the muscle itself. A tendon is simply
a continuation of that connective tissue
except now the collagen proteins
are all going in one single direction.
Now, as that tendon approaches
and begins to merge with the bone itself,
this is where the differences between a
fibrous and a fibrocartilaginous enthesis
emerges. Fibrous enthesis are relatively
straight forward. The collagen from the
tendons will blend with the periosteum of a
bone. Periosteum is that connective tissue
outer wrapping of a bone and depending
on the muscle, the collagen from the tendon
may actually penetrate deeper into
the dense compact bone underneath.
A Fibrocartilaginous enthesis on the other hand,
I mean, it does very similar but instead as it's
approaching the periosteum, the collagen will
start to transition into cartilage cells and then
again, it can continue going to the periosteum and
the compact bone but because there's cartilage,
that's going to affect how energy
is transmitted between the tissues.
Most studies have been focused on the
fibrocartilaginous enthesis because honestly
that's just the most common type of enthesis
in the body. In the field of osteoarcheology,
scientists are in a constant pursuit to
understand the shape and size of an
enthesis and how that may relate to the
physical activity in someone's lifetime.
Bones are capable of reshaping themselves based
around activity. In fact, Jonathan did an entire
video already on how exercise can shape your
bones. So, be sure to check that out after this
video but I want you to picture this - let's say
a forensic anthropologist is called in to identify
or investigate skeletal remains that are found in
a forest. If they were able to look at the shape,
size, and location of these enthesis and then
in infer, you know, it was a construction worker
- played piano, so on and so forth. That would
dramatically speed up the investigative process.
It's also useful in helping to
determine the physical lifestyle of
our human ancestors such as Homo Naledi or Homo
Heidelbergensis and plenty of others. Although,
there are other factors that go into determining
the shape and size of these enthesis such as age
and sex. So, unfortunately, it's not as simple
as just to say, Oh, it's shaped and sized like
this because of physical activity. It's - it's
complex but now that we understand that nature is
constantly experimenting through the evolutionary
process, let me ask you another question:
Do you think there may be some value
in shifting the location of an enthesis
in order to create a difference in leverage? The answer is yes.
Not only are muscle shapes and
sizes variable but the location with which
they attach on the skeleton can also vary.
Now, I don't want to make it seem as though,
you know, the translocation of this
enthesis is going to be huge. I mean,
you don't want muscles just attaching
everywhere willy nilly, that would be very bad.
Instead, the enthesis might have just shifted
a couple millimeters or less to some different
location on the same bone but that small shift
can have very large consequences in regards to
leverage. It's entirely possible that a muscle or
two or more in your body are attaching a slightly
different location than what we teach in
the textbooks making you slightly faster
or stronger depending on the muscle and the
available range of motion so on and so forth.
How much faster how? Much stronger?
I couldn't tell you, right? We would
need to take the measurements
and then do the math to figure it out
but this is the struggle when it comes to
determining what is "anatomically normal".
It's not as though the textbooks are wrong or
anatomy is just wildly inconsistent. In fact,
anatomists are able to determine what is
considered normal based around repeated
observations. Traits within populations
can and do shift over time. That's just
the evolutionary process but this is
why anatomists typically favor a range of
normality as opposed to a strict and unwavering
normality but from a teaching standpoint,
that would just be brutally difficult
to do in an intro to anatomy course.
Can you imagine sitting in the
classroom and your instructor says,
"for the most part", after everything they teach,
it would be the most confusing class in the world.
Intro anatomy courses are teaching students the
structures and processes that have been observed
the most over hundreds of years of rigorous study.
I have no problem saying that it's normal for
a human to have two arms, two legs, a brain,
a liver, an epidermis, or biceps brachii that
originates at the super glenoid tubercle,
the coracoid process and inserts
at the radial tuberosity. Just because
there may be a range of normality
doesn't mean that it's unreasonable
to expect things to be structured
a certain way most of the time.
Personally though, what I to be the most
interesting are the edge cases in the bell
curve of normality. Look, we're not finding
any new structures in the human body. In the
event that you see a headline that says,
"Anatomist discovered new structure".
They probably didn't. Anatomist have likely known
about that for quite some time. The problem just
came down to likely classification as
well as determining its exact function.
Instead though, we are still finding
new variable tissues and structures in the
body and trying to figure out how that
relates to the body's overall function.
I would not be surprised if many of
the best athletes in the world have
variabilities that are either bordering or
simply outside of the range of normal and
it positively affects their performance in
ways that you just cannot train for, right?
If I just dropped everything and
decided to become an elite swimmer,
that doesn't mean I can do it at least in a highly
competitive fashion, right? Bodies are different,
people are Different. It's not to say that
athletes don't work extremely hard because
they do. It's just saying if we really started
looking into the nuances of these things,
it wouldn't be surprising if we're
finding, oh look, Michael Phelps had a
muscle attached in a slightly different
position or something along those lines.
In fact, to me, this is just really interesting
about the human body because what it shows us
is that really, truly, quite literally, some
people are just built different. Thanks for
watching everybody. Be sure to click the
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free report from Yogabody Teachers College
today. As all be sure to like, comment,
subscribe if you feel so inclined
and I'll see you in the next video.