Beauty BENEATH The Skin: A Sack Of Bony Levers And Fluid-Filled Joints

try 2

My latest blog-buster is not exactly great world literature, but it is chopful of valuable information.  The book is called Essentials of Strength Training and Conditioning.  It is by Thomas R. Naechle  and Roger W. Earle, and it comes to us from the National Strength And Conditioning Association.   It’s a college textbook, a fairly standard one I assume, and perhaps the preeminent one.  It will take me several blogposts just to skim the surface of all its vast offerings.  My approach to the book is mainly from the perspective of a weightlifter, so my entries will frequently touchback to that theme.

For my first entry on the book, I want to begin by briefly describing what I learned about human musculature.  In the later entries I’ll talk about nutrition and supplements, and then maybe we’ll pop into the gym for some tips on weightlifting that will make more sense once you understand a little bit more of what’s going on beneath the skin.

A picture’s worth a thousand words when it comes to describing and understanding the human anatomy, so I strongly advise you to search for clear diagrams or “maps” of how the body is put together in order to better comprehend these entries, which will of themselves remain relatively light and shallow as far as biology-instruction goes.

Before getting into how muscles manipulate the bones of the body, let us briefly review the human skeleton…

The human body’s whole hot mess (98.6 degrees), is kept from collapsing into a skin-sack full of bloody jelly and internal organs by the human skeleton.  The skeleton’s rib cage and cranium protect most of the vital stuff, and it seems to me that most things hang directly or indirectly off the spine, probably going back to ancestral days when we walked at least some of the time on all fours, and so the spine was usually kept in more horizontal positions than we tend to keep in our non-hanky-panky waking hours today.  In those days, our organs and spinal discs would have hung down more freely, instead of setting atop each other in the rather smushed-together, modern fashion.

All the big-movement muscles of the body use the bones of the skeleton as levers to move the body around (exceptions would include muscles like those of the face or heart or tongue).  Because muscles are a one-trick pony (contracting is their main skill), they are actually only capable of pulling on the levers.  Even when we are pushing something– we are actually pulling… on our own bones.

Many of the beautiful and graceful (and not so graceful) movements of the human body are conducted by the manipulation of many of its approximately 206 bones by many of its approximately 430 muscles.

Just for the record, let’s quickly run through the main parts of the skeleton.  I’m not going to describe the skeleton in detail, but I suggest you look at a bone-map to aid in visualization.

THE HUMAN SKELETON…

1) The Main Line:  cranium, spinal column, ribs, sternum;  the spinal column has over thirty vertebrae: 1 thru 7 in the neck, 8 thru 19 in the upper and mid back,  and vertebrae 20 thru 24 in the lower back (the “Lumbar” region).   At vertebra 25 the weirdness sets in.  Vertebrae 25 thru 29 are fused together to make the back of the pelvis.  Most people assume that the last three-to-five vertebrae (the number varies between individuals) are leftover from some kind of tail, and the odds are that they’re correct… but personally, I don’t rule-out the possibility that the area (called the coccyx) is just part of the basic, adaptable design of the general set of mammalian blueprints, and that we’re set to have a tail if evolution ever decides we need one (I’d gladly take one if it was prehensile!).

2) The Secondary Line:  pectorals, the scapulas and clavicles, the pelvic girdle

3) The Limbs:  Arms (from the shoulder: humerous, radius, ulna, carpas, metacarpals, phalanges);  Legs (from the hip: femur, patella, tibia, fibula, tarsas, metatarsals, phalanges)

While we’re on the subject of the skeleton, you may hear people talk about the proximal versus the distal end of a muscle.  This is simple:  the proximal end of a muscle is nearer (proximate) to the trunk, and the distal end is more dis-tant from the trunk.

The first step in voluntary movement (after the metaphysical part about deciding to move) is the sending of signals from the brain and nervous system out to the muscles which we want to move (actually, we don’t really think about which muscles we want to move– we just know we want to use, say, our right hand to grab that beer mug and bring it –gently– to our lips).  Luckily for us, our brain is smarter than we are.

Nervous system signals are either “on” or “off” (in that binary way of conducting business Nature has at its most basic level).  The “on” is the instruction to the muscle to contract.  Otherwise, the muscle is “off”– relaxed.  When the muscles contract, they shorten lengthways.  This shortening causes the muscle to pull-in at the ends– at the places where it is anchored, via tendons, to the bone.  The contracting muscle pulls-in the tendon, and the tendon in turn tugs at the bone– and voila!– movement ensues.

The change from muscle to tendon is so continuous, it is not as easy as you might think to draw a line and say, on this side is muscle, on this side tendon.  As our authors tells us, tendons “blend into and are continuous with both the muscle sheaths [surrounding the muscle] and the connective tissue surrounding the bone.”  Furthermore, tendons “have additional fibers that extend into the bone itself, making for a very strong union.”

Fibrous connective tissues cover:  each muscle fiber, each bundle of muscle fibers, and each bundle of muscle bundles (the “muscle,” itself).  Our authors tell us that all three levels of this connective tissue (called respectively the endomysium, the perimysium, and the epimysium) are “continuous with the tendon.”  The tendon is so intricately woven to the end of the muscle that it could almost be said to be an extension of the muscle.  Due to this intricate connection between the tendon and the muscle fibers, the bundles of fibers, and the overall muscle– the tension created by the contraction of each individual muscle cell’s contraction is summed and securely communicated to the tendon.

Furthermore, each bone is covered by its own connective tissue called periosteum, and the tendon connects to this.  Thus, securely anchored at both ends, the tendon serves as a very strong bridge between the muscle and the bone.

People vary in precisely how their tendons attach to the bone, and this seemingly small detail can actually result in substantial differences in strength between individuals.  As our authors write, “a person whose tendons are inserted on the bone farther from the joint center should be able to lift heavier weights because the muscle force acts through a longer moment arm and can thus produce greater torque around the joint.”  Of course, there’s a trade-off for that increased strength (there’s always a trade-off)… Such strength-increasing tendons can slow down a person’s movement since “with the tendon inserted farther from the joint center, the muscle has to contract more to make the joint move through a given range of motion.”

Besides causing movement, muscles can also act to slow or stop movement.  Muscles causing movement are called “agonists.”  Muscles putting on the brakes are called “antagonists.”  Depending on the activity, most any bone-lever-pulling muscle can serve as either an agonist or an antagonist.  The reason we need the antagonist is so we don’t destroy our own joints by slamming them too wide open, too fast.

Speaking of joints, here’s a little something to get you higher (in your level of knowledge)…

There are basically two different classifications of joints:  roaches and blunts– no, no– jk…

There are basically two different ways we can divide joints:  1) by how they fit together, and  2) by what they are made of.

.

How Joint’s Fit Together

Joints can rotate around…

1) a single axis, like the elbows or knees (actually the knee is slightly more complicated than a simple single axis since its axis of rotation shifts during the range of its motion)

2) a double-axis, like the ankle and wrist (left to right, up and down), and…

3) a ball-and-socket joint, like the shoulder and hip, which have incredible range of motion

.

How Joints Are Put Together

You can have…

1) Fibrous Joints— like the sutures of the skull… if you’re lucky, there’s very virtually no movement at these joints

2) Cartilaginous Joints— such as those of the disks located between the vertebrae of the spine; these allow limited movement

3)  Synovial Joints— these are what most of us think of when we think of joints (well, depending on your life-style choices);  in synovial joints, like those of the elbow and knee;  the entire joint is enclosed in a capsule of “synovial fluid;” also,there’s usually ligament and cartilage around for support and for movement-enhancement, like the hyaline cartilage covering the end of the bone where it meets the joint

In the next post, I’ll talk more about what is going on inside the muscle once it receives the signal to contract.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s