The Human Back Is A Design Disaster

July 18, 2019

Everyone who lives long enough is likely to experience back pain. And the cause isn't just aging. We have evolution to blame for a spine that's an engineering nightmare. Cheddar Explores how our spines changed to accommodate human bipedalism.

FULL TRANSCRIPT

Speaker 1: Of all the reasons people go see their doctors worldwide,

Speaker 1: back pain comes in right at number 6.

Speaker 1: Back pain is coming for us all.

Speaker 1: You, your friends, your parents,

Speaker 1: everyone you've ever known,

Speaker 1: if you live long enough,

Speaker 1: you're gonna get back pain.

Speaker 1: Oh yes, you're thinking "Well,

Speaker 1: that's just aging, isn't it?"

Speaker 1: Doesn't everything decay and

Speaker 1: crumble as we hurtle towards oblivion?

Speaker 1: Well, yes.

Speaker 1: But also humans are the only mammals to

Speaker 1: suffer many of these musculoskeletal maladies.

Speaker 1: You don't hear chimps and gorillas

Speaker 1: complaining about their herniated discs.

Speaker 1: I bring up chimps because chimpanzees share

Speaker 1: a common evolutionary lineage with us.

Speaker 1: So understanding how our anatomy differs from

Speaker 1: our chimp cousins can help us

Speaker 1: understand some of the mysterious aches,

Speaker 1: and pains, and quirks about us.

Speaker 1: Why pregnant women waddle like this

Speaker 1: or why your grandma gets

Speaker 1: shorter and stooped over like this.

Speaker 1: Essentially, it can help us understand why

Speaker 1: the human spine is an engineering nightmare?

Speaker 1: [MUSIC] Let's run through some of

Speaker 1: the greatest hits from

Speaker 1: the musculoskeletal problems that

Speaker 1: affect only humans and not other mammals album.

Speaker 1: Fractured hips, bunions, hernias, fallen arches,

Speaker 1: torn meniscuses, shin splints, herniated discs,

Speaker 1: fractured vertebrae, spondylolysis, scoliosis,

Speaker 1: kyphosis, osteoporosis, just to name a few.

Speaker 1: All of this pain can be traced to

Speaker 1: arguably the most important adaptation humans

Speaker 1: made, standing upright.

Speaker 1: This one very human feature causes two big issues.

Speaker 1: Let's break them down, taking

Speaker 1: a short stiff horizontal spine

Speaker 1: that was adapted for climbing,

Speaker 1: and trying to balance our big heads over

Speaker 1: our 26 vertebrae and our feet is a tall order.

Speaker 1: Evolutionary anthropologist, Bruce Latimer,

Speaker 1: studies the evolution of human locomotion.

Speaker 1: He compares this task to trying

Speaker 1: to stack 26 tea cups and saucers,

Speaker 1: and then balance a human head on top of them.

Speaker 1: To make this configuration possible,

Speaker 1: we evolved some anatomical quirks.

Speaker 1: Latimer uses the fossil record,

Speaker 1: as well as data about modern apes and

Speaker 1: modern people's spines to trace

Speaker 1: the evolution of these mechanical changes.

Speaker 1: [MUSIC].

FEMALE_1: [MUSIC] Chimpanzees have

FEMALE_1: a straight stiff spine which supports climbing.

FEMALE_1: Our spine is flexible and curvy

FEMALE_1: which supports our weird upright gait.

FEMALE_1: You probably know this spot in the

FEMALE_1: lower back as the iconic resting place for

FEMALE_1: your hands when you're complaining about how getting old

FEMALE_1: is the worst and your back just isn't what it used to be.

FEMALE_1: Its anatomical name is the Lumbar Lordosis.

FEMALE_1: Our spine had to curve

FEMALE_1: inwards here to avoid the birth canal,

FEMALE_1: while also keeping the torso balanced over the feet.

FEMALE_1: This is why women who are very

FEMALE_1: pregnant sometimes lean back this way.

FEMALE_1: It's to correct for the way the weight of

FEMALE_1: the fetus throws off the center of balance.

FEMALE_1: While these bends and our spine

FEMALE_1: help us balance and walk upright,

FEMALE_1: from an engineering standpoint,

FEMALE_1: they're weak spots just begging for failure.

FEMALE_1: Meet T8, the most

FEMALE_1: commonly fractured vertebra in the spine.

FEMALE_1: It's had a mechanically weak location.

FEMALE_1: Plus as we age and our discs and joints get worn down,

FEMALE_1: we get more and more likely to suffer a break.

FEMALE_1: And once T8 goes,

FEMALE_1: you've changed the load bearing situation of the spine,

FEMALE_1: and it's not long until T12 and L1 break.

FEMALE_1: And when that happens, you're putting pressure on

FEMALE_1: the large joints at the bottom of

FEMALE_1: the spine until they break.

FEMALE_1: This is the reason your grandma gets shorter

FEMALE_1: and stooped over and gets a dowager some.

FEMALE_1: Okay. That's the first big problem.

FEMALE_1: The curves are mechanical weak spots.

FEMALE_1: Here's another big factor, our gait.

FEMALE_1: Whether you're a human, a flea, an ostrich,

FEMALE_1: or a tiger, you've got to do

FEMALE_1: two things to get anywhere in this world.

FEMALE_1: You need to create enough force and friction

FEMALE_1: with the ground to propel yourself forward.

FEMALE_1: And you also need to protect your body from

FEMALE_1: the force that's generated each

FEMALE_1: time your feet strike the ground.

FEMALE_1: Don't underestimate the importance

FEMALE_1: of this aspect. It's critical.

FEMALE_1: Latimer uses a Siberian tiger

FEMALE_1: to illustrate his point here.

FEMALE_1: When an 800 pound tiger is galloping at 35 miles an hour,

FEMALE_1: the force that's being generated each

FEMALE_1: time its paws hit the ground is enormous,

FEMALE_1: enough to blow the cat to pieces.

FEMALE_1: In quadruped like the tiger,

FEMALE_1: their tricep and shoulder

FEMALE_1: muscles contract and elongate in a special way that

FEMALE_1: absorbs the mechanical energy and

FEMALE_1: disperses it as harmless heat.

FEMALE_1: But because we traded in four limbs for arms,

FEMALE_1: we don't have our shoulder muscles

FEMALE_1: available as shock absorbers.

FEMALE_1: In humans, all of

FEMALE_1: that force is entering the body through a single point,

FEMALE_1: our heel, and then traveling up our leg.

FEMALE_1: So we rely on the muscles of our lower legs

FEMALE_1: to absorb that energy and protect our joints.

FEMALE_1: When your heel strikes the ground,

FEMALE_1: you flex your knee around five to six degrees,

FEMALE_1: allowing the quad to absorb the energy.

FEMALE_1: And in the push off stage,

FEMALE_1: when the ball of your foot pushes off the ground,

FEMALE_1: the quad muscle contracts,

FEMALE_1: which creates the force against

FEMALE_1: the ground that propels you forward.

FEMALE_1: That's a lot of force coming through one contact point,

FEMALE_1: so you've adapted our gait to mitigate all that pressure.

FEMALE_1: With each step, you throw your right arm

FEMALE_1: and left leg forward at the same time.

FEMALE_1: Basically, we're constantly twisting.

FEMALE_1: That's our adaptation for further dispersing

FEMALE_1: the torsional load from our weirdo bipedal gait.

FEMALE_1: If we didn't make this twist,

FEMALE_1: the reactive force from the ground would be

FEMALE_1: strong enough to spin you around.

FEMALE_1: This twisting is another major source

FEMALE_1: of our back problems.

FEMALE_1: In between each bone in your spine,

FEMALE_1: there rests a cushion of

FEMALE_1: collagen with a mucus protein gel filling.

FEMALE_1: This cushion is the entire vertebral disc.

FEMALE_1: Its structure is often

FEMALE_1: compared to that of a jelly doughnut.

FEMALE_1: Um, the discs allow our spine to

FEMALE_1: twist and flex and

FEMALE_1: absorb some of the ground force reaction.

FEMALE_1: They also help evenly distribute

FEMALE_1: the load that our spine is supporting.

FEMALE_1: But twisting all day, every day,

FEMALE_1: millions of times over

FEMALE_1: our lifetime really does a number on the discs.

FEMALE_1: The tough outer layer wears out.

FEMALE_1: Sometimes the jelly escapes the doughnut.

FEMALE_1: When that happens, you've got a herniated disc.

FEMALE_1: The jelly can push into nerves causing pain or numbness.

FEMALE_1: By the time we hit 50 or 60,

FEMALE_1: we are all looking at that pain.

FEMALE_1: Some of us will see it earlier or worse than others too.

FEMALE_1: If you're a gymnast or you

FEMALE_1: swim the butterfly for instance,

FEMALE_1: you're putting your lumbar low doses through

FEMALE_1: some intense pressure and wear and tear.

FEMALE_1: If you carry weight,

FEMALE_1: you're putting more load on the spine and its discs.

FEMALE_1: And of course, if you do a lot

FEMALE_1: of repetitive twisting, lifting,

FEMALE_1: or pulling at your job,

FEMALE_1: that's adding more twist and load cycles

FEMALE_1: to the spine and the discs as well.

FEMALE_1: We can try to stave off the worst of it by strengthening

FEMALE_1: our core muscles for added spinal support and stability.

FEMALE_1: And we can also remember that

FEMALE_1: this is a relatively small price to pay.

FEMALE_1: Standing upright is what makes us human.

FEMALE_1: And the number 1, most successful primates.

FEMALE_1: [MUSIC].