Human skeleton 101

I believe if you have been exercising for a while you know the feeling of wanting to know more. Exercise is such a beautiful thing, because it seduces us with very concrete and desirable goals like a stronger body, but slowly but surely it take us into the marvels of the human body. So this article is a call to that curiosity: so we don’t only stay with the what’s and how’s, but we also explore the why’s. This time, it is about the skeleton.

The human skeleton has written within it a history of adaptation. Let’s take a look at it.


As difficult as making sense of all this bones may seem, there is a certain logic behind it. Think of that very same human being, only walking on four legs. You would immediately have very striking facts, like these:

  • The extremities have identical structures. This suggest a time when we were quadrupedal animals. Both the arms and legs start with one bone – the humerus and femur. After this there is a hinge joint, the elbow and knee, meaning joints that allow mostly flexion and extension, not rotation. This joints are mostly about connecting more complex joints, standing a lot of pressure but also being limited in their mobility. This area from the shoulder to the elbow and from the hip to the knee comprises the upper portion of the extremity, and in the lower portion there are also similarities – two bones (Radius and ulna in the arm, Tibia and fibula in the legs). This ends with the wrist and ankle, where on both cases there are three carpals, followed by four carpals, five metacarpals and five phalanges.
  • Both extremities start with ball & socket type joints- the shoulder and the hip. This type of joints allow the greatest range of motion possible, but are also the most prone to injury.
  • Both the shoulder joint and the hip joint connect to bigger bones – the scapula and the pelvis. This structures determine the position and health of the extremities, and connect them to the spine.
  • There is a difference, though. When we got to stand upright in our evolutionary history our arms specialized in manipulation, and our legs in locomotion. This had the effect of the shoulders being designed for mobility over stability, and the hip being designed for stability over mobility. This is why the scapula is a floating bone, allowing the greatest amount of mobility in the human body, whereas the pelvis has a bonny connection to the spine.
  • Finally, the clavicle separates the two arms in order for us to be able to stand both compression (push) and tension (pull) forces over them. We moved from the arms to the side design fish and reptiles have to an arms to the front design that four leg creatures like dogs have, to finally have a collarbone that comes from our arboreal past and makes our arms not only being designed for staying close to our body but also to extend, grab and manipulate.

That’s it for the extremities. Now let’s take a look at the spine and all the middle compartments of the skeleton.

Image from Atlas of Human Anatomy, by Frank H. Netter

Take a look at that marvel. We won’t get into all of the little details, but on the big picture we can see:

  • We have four portions in our spine. From top to bottom, the cervical, thoracic, lumbar and sacral area. We will talk about the coccyx in just a moment. Remember that thing about the hip area being designed for stability over mobility? It is the same in the spine. The cervical area has the most mobility, where the first two vertebras, the atlas and axis, allow a great range of motion for the head, senses and specially the eyes to be able to guide us around. The thoracic curve allows mobility too, but stability starts to become more important here. This is the connection of your neck with your lower back, where the lumbar curvature is the strongest part of your spine but also the less mobile. Finally, the sacrum is deep within our body, having of course very little mobility.
  • The cervical area and the sacral area both compensate each other in terms of position. When you move one, the other one adapts to it to keep balance in a body that has to constantly withstand the force of gravity. The thoracic and lumbar portions of the spine just transmit this compensations between the farthest points of the chain.
  • If the latter is so, what about the coccyx? That is, probably, the root of a tail we used to have and we no longer do. Animals use their tails for communication, locomotion but also for balance. The difference in us would be then that, due to our rise from the ground to stand on two feet, the great balance compensations that used to happen mainly between the head and the tail moved a little bit closer when we lost our tail, so now it happens between the cervical and sacral area of the spine.
  • There are two key areas that are responsable for the uprightness and spring of our skeleton. The first one is around L4-S1 (the letter stands for the area of the spine, in this case, the lumbar and sacral area, and the number means the specific vertebra, which go from low to high in the feet direction). Here is the convergence of two forces: from the ground there comes a force that is carried through your feet and legs and that pushes your body upwards, and from your head and torso comes a force that moves your body downwards, which is called weight. When this area is balanced the spine can remain upright and not collapse under the force of gravity, or do it without a great deal of effort. The second area is at T5-T6 level, where the level of flexion of your upper torso is managed, thus being responsible for the spring of your spine. This two areas are children of our evolutionary process of standing upright.
  • Regardless of the last paragraph, what really holds the skeleton up is the muscles. The bones by themselves just hold everything together but, without the muscular system, the skeleton would be nothing but a pile of bones lying on the floor.

I think that is enough for today. I hope you enjoyed this little journey inside the marvel of our skeleton. I also hope that this was not only information, but a gateway into more curiosity, awareness and empathy for something as amazing as yourself.

If you want to know more about these topics, I’d recommend the work of Tom Myers and Lee Parore

Kinema Project products

Pliable body (Get flexible fast!)

The Dynamic Structure (Bulletproof your joints!)

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