How do muscles help erect the spine?

Muscles of the spine help to support it against gravity. For example, the multifidi interweave throughout the vertebrae and, as I understand, sort of reinforce the spine. So let's suppose muscles help to make the spine more stiff and rigid and this somehow helps it fight gravity.

What portion of support comes from the muscles? Would a spine by itself be able to support itself? In other words, to what extent is our ability to support our spine to remain upright due to muscles and how exactly do they help keep the spine erect in this capacity?

A biomechanical analysis can be done to determine how much support comes from the muscles vs other (skeletal) support structures. Assume the body is standing upright, in static equilibrium. Consider this (over simplified) free body diagram of the upper torso where the sum of the forces equals zero in static equilibrium.

Here the diagram over simplifies the analysis with one general equation: Fsupport = sum of all the weights. Since we are considering only how much weight muscle supports, we deduct Wbones from Fsupport.

A spine by itself would not be able to support itself because the sum of the forces do not equal zero in static equilibrium. (Wgravity + Wspine) > Fsupport.

In reality, each muscle, bone, and organ has many more forces with specific magnitudes in different directions that altogether equal the weight of the specific region of mass it supports. I imagine these forces as many vectors over an area/field. A more detailed analysis would require a program like MATLAB that uses triple integrals in calculus to visualize these forces in 3D. This kind of visualization can help us color code only the muscle vectors which answers your question, "to what extent is our ability to support our spine to remain upright due to muscles," as a percentage of the sum of all the forces input into the program. How the muscles keep the spine erect can be determined from such visualizations as descriptions of directional forces.

For an example of how this kind of analysis is done, see this paper on lumbar spinal support.

Spine is the only element between thorax and pelvis that can support compressive stress, and thus the weight of the upper body. So the spine needs to support all that.

However, the spine is not rigit enough, and would buckle without muscles. Muscles stabilize it by pulling in a coordinated manner, just as ropes can help stabilize an erected mast. The paper cited by Anna Lu,, illustrates this, and states that muscles have both an active role (their relative tension can be tuned) and a passive role (they behave as elastic ropes).

Note however, that this is done at the price of exerting even more compressive stress on the spine!

Erector Spinae Strengthening Exercises

If your back is aching and tired, weak muscles may be to blame. The erector spinae are muscles that run along the spine and are the primary muscles that help you rise back up when you bend over. With an inactive lifestyle, these muscles become weak, which puts you at risk for back strain. To reduce your aches and prevent injury, add some back-strengthening erector spinae exercises to your routine.

The Connection Between Lower Back Pain and Erection Problems

One of the most common health complaints among Americans is lower back pain, which affects up to two-thirds of all men and women at some point in their lives. Less widely recognized is the association between chronic low back pain and erectile dysfunction.

For centuries, writers have likened human anatomy to a marvel of engineering and art, both complex in its design and beautiful in appearance. Like an expensive car, the body is an assemblage of individual components that function smoothly together as long as all of those components are scrupulously maintained. Let one part go unattended to, and it may eventually fail, setting off interactions with other components that may cause them to fail or perform poorly.

Interconnectedness of Bodily Structures

When one considers the interconnectedness of all the structures and organs of the human body, it becomes somewhat easier to see how problems in one area can quickly turn into problems for other areas too.

In an article posted at, California physiatrist Christina Lasich, M.D., a specialist in pain management and spine rehabilitation, cites a recent study of men under 50 with lumbar spine disease. More than one-third of those men, relatively young in age, suffered from erectile dysfunction too.

Physiatry, for those unfamiliar with the term, is a medical discipline that seeks to restore and enhance functional ability and quality of life to people suffering from physical disability or impairment.

Research into Subject Limited

Despite the high incidence of erectile dysfunction among men with chronic back pain, many of them still relatively young, the link between back pain and ED has not attracted the research attention it deserves, according to Lasich. She says that many lay people theorize the ED among back pain sufferers is caused somehow by hormonal imbalances, such as those caused by long-term opioid use to manage pain. She points out, however, that low blood levels of testosterone are not known to cause ED.

Rather, Lasich suggests, the link between spinal problems and ED is more likely to arise from problems related to the nervous system. She points out that erectile function is controlled by “two different nerve centers in the spine: the parasympathetic input from the sacrum and the sympathetic input from the thoracic-lumbar pathway.” Any damage to the these areas of the spine, whether traumatic or because of neglect, can lead to sexual dysfunction.

Spinal Surgery Might Not Help

And erection problems that arise from spinal injury or disease will not necessarily disappear once the spine is repaired. Lasich notes that another study of men under 50 who underwent spinal surgery showed that the resulting improvements in erectile function were minimal.

Lasich is quick to point out that surgery to correct spinal damage can sometimes salvage sexual function. She cites the case of a 35-year-old man who had suffered from mild ED since the age of 18. In his case, spinal surgery did lead to improvements in erectile function. Anecdotal evidence indicates that men with mild erection problems are more likely to regain normal erectile function after spinal surgery.

Back Pain Hardly Conducive to Sex

As previously noted, chronic low back pain can lead to erection problems in men. However, both men and women who experience acute episodes of lower back pain may find it difficult to get excited sexually, wincing at the very thought of how sexual activity might aggravate the pain they’re already enduring.

This relationship between back pain and sexual dysfunction makes it important for those with chronic back pain to discuss their concerns with their sexual partners and their doctors as well. Sexual dysfunction related to back pain “is probably more common than physicians think and for patients to admit to,” according to Michael R. Marks, M.D., a spokesman for the American Academy of Orthopaedic Surgeons. In an interview with, he said he makes it a practice to routinely quiz his back pain patients about the impact of the disability on their sex lives.

Some Patients Reluctant to Talk Sex

Marks acknowledges that it’s sometimes difficult to get to the truth about the effects of back pain on the sexual function of his patients. While some welcome the opportunity to discuss the effects of their pain on sexual intimacy, most won’t broach the subject voluntarily, he says.

Given this natural reluctance of most back pain patients to bring up the subject, many doctors in his field are happy to let the matter go unaddressed, says Marks. To back pain patients with concerns about their pain’s impact on sexual function, he urges them to bring up the subject themselves.

Erectile Function Explained

As most men today are aware, an erection begins not in the penis but in the brain. When the brain receives signals of physical stimuli to the genitals or generates feelings of sexual desire, it sends a flood of nitric oxide coursing toward the pelvic region. On its way, the nitric oxide triggers secondary chemical reactions, one of which leads to the synthesis of a substance known as cyclic guanosine monophosphate, or cGMP.

A major player in erectile function, the cGMP signals the smooth muscle tissue that lines the inner walls of arteries to relax. As the muscle tissue relaxes, arteries dilate, thus increasing the volume of blood they can carry. This facilitates the erection process that requires robust blood flow to achieve and sustain erection.

How Back Pain Affects Sexual Function

There are a number of ways in which the body parts involved in back pain can interfere with erectile function, according to Kenya-based physical therapist Eunice Kabana. In an article posted at, she considers three specific links between chronic back pain and erectile dysfunction.

  • Hip flexors are the muscles that run from the lumbar spine through the groin to the hip. When these muscles tighten, they cause compression in the pelvic region that can impede blood flow. And, as you’ve seen, strong blood flow is essential for optimal erectile function.
  • Spinal stenosis, a narrowing of the space between individual vertebrae, can put undue pressure on the nerves and blood vessels that pass through those spaces. Among the nerves that might be pinched in such cases is the pudendal nerve that carries sensation from the external genitalia to the brain, control center for the nervous system.
  • Herniated discs, a rupturing of the fibrocartilaginous discs that separate one vertebra from another, can interfere with a wide array of bodily functions, not the least of which is erectile function.

Doing Nothing Isn’t the Answer

The natural reaction to acute pain in the lower back is to do nothing for fear that virtually any movement will exacerbate the underlying condition and increase pain. However, certain exercises can help to strengthen the back and relieve the pain. At the same time, other exercises that might be worthwhile for those without back problems can aggravate the situation, according to Check with your doctor or physical therapist to help you develop an exercise program tailored specifically to your condition.

Some exercises that can help strengthen the back and relieve pain include partial crunches, hamstring stretches, wall sits, and press-up back extensions. You should probably avoid leg lifts, toe touches, and sit-ups.

Maintaining flexibility, including in the legs, can help with lower back pain.

How to Do Them

To perform partial crunches, lie on the floor or exercise mat with knees bent and feet flat on the floor. You can put your hands behind your neck or cross your arms over your chest. Tighten your stomach muscles and raise your shoulders off the floor. Don’t use your arms to pull your neck off the floor or lead with your elbows. Once you’ve reached a raised position, hold it for a second and then slowly lower your back to the floor. Repeat 10 or 12 times.

For the hamstring stretch, lie on your back with one knee bent. Loop a towel under the ball of your other foot. Slowly pull back on the towel raising the leg until you feel a gentle stretch down the back of leg. Hold that position for 15 to 30 seconds. Do two to four times for each leg.

Doing a Wall Sit

To perform a wall sit, stand 10 to 12 inches with your back facing the wall. Lean back until your back is flat against the wall and then slowly slide your back down the wall until your knees are slightly bent, taking care to keep your back flush against the wall. Hold that position for about 10 seconds and then slowly slide your back up the wall again. Repeat 8 to 12 times.

For press-up back extensions, lie on your stomach with your hands planted on the floor palms down directly beneath your shoulders. Push against the floor with your hands to slow raise your shoulders above your hands. If you can comfortably do so, put your elbows on the floor below your shoulders and hold that position for several seconds.

ED Drugs Might Help

Viagra and the other oral ED drugs that temporarily improve blood flow to the penis can help some men who suffer from erection problems related to lower back pain. How much they help depends to a large degree on the amount of damage done to the nerves and blood supply that are involved in erectile function.

How to Straighten Your Spine

This article was co-authored by Karen Litzy, PT, DPT. Dr. Karen Litzy, PT, DPT is a licensed physical therapist, international speaker, owner of Karen Litzy Physical Therapy, PLLC, and the host of the Healthy Wealthy & Smart podcast. With over 20 years of experience, she specializes in a comprehensive approach to practicing physical therapy utilizing therapeutic exercises, manual therapy, pain education, and home exercise programs. Karen holds a Master of Science in Physical Therapy and a Doctor of Physical Therapy from Misericordia University. Karen is a member of the American Physical Therapy Association (APTA) and is an official spokesperson for the APTA as a member of their media corps. She lives and works in New York City.

There are 19 references cited in this article, which can be found at the bottom of the page.

wikiHow marks an article as reader-approved once it receives enough positive feedback. This article received 12 testimonials and 83% of readers who voted found it helpful, earning it our reader-approved status.

This article has been viewed 1,665,726 times.

The spinal column runs down the middle of your back and contains the spinal cord, which is like a superhighway of nerves that connect your brain to every tissue in your body. Needless to say, the health of your spine is of paramount importance. From the lateral or side view, your spine contains three main curves, which are needed for flexibility and stability. [1] X Research source However, viewing your spine from the back, it should be straight and not deviate from side-to-side very much at all. Some people are born with abnormally curved spines, but ill health, poor posture and inadequate nutrition are more responsible for spinal pathology.

Management and Treatment

What are the treatments for spinal stenosis?

Choice of stenosis treatments depend on what is causing your symptoms, the location of the problem and the severity of your symptoms. If your symptoms are mild, your healthcare provider may recommend some self-care remedies first. If these don’t work and as symptoms worsen, your provider may recommend physical therapy, medication and finally surgery.

Self-help remedies include:

  • Apply heat: Heat usually is the better choice for pain due to osteoarthritis. Heat increases blood flow, which relaxes muscles and relieves aching joints. Be careful when using heat – don’t set the settings too high so you don’t get burned.
  • Apply cold: If heat isn’t easing your symptoms, try ice (an ice pack, frozen gel pack, or frozen bag of peas or corn). Typically ice is applied 20 minutes on and 20 minutes off. Ice reduces swelling, tenderness and inflammation.
  • Exercise: Check with your healthcare provider first, but exercise is helpful in relieving pain, strengthening muscles to support your spine and improving your flexibility and balance.

Non-surgical treatments include:

  • Oral medications:Nonsteroidal anti-inflammatory medications (NSAIDs) – such as ibuprofen (Advil®, Motrin®), naproxen (Aleve®), aspirin – or acetaminophen (Tylenol®) can help relieve inflammation and provide pain relief from spinal stenosis. Be sure to talk with your healthcare provider and learn about possible long-term problems of taking these medicines, such as acid reflux and stomach ulcers. Your healthcare provider may also recommend other prescription medications with pain-relieving properties, such as the anti-seizure drug gabapentin (Neurontin®) or tricyclic antidepressants such as amitriptyline (Elavil®). Opioids, such as oxycodone (Oxycontin®) or hydrocodone (Vicodin®), may be prescribed for short-term pain relief. However, they are usually prescribed with caution since they can become habit forming. Muscle relaxants such as cyclobenzaprine (Amrix®, Fexmid®) can treat muscle camps and spasms.
  • Physical therapy: Physical therapists will work with you to develop a back-healthy exercise program to help you gain strength and improve your balance, flexibility and spine stability. Strengthening your back and abdominal muscles — your core — will make your spine more resilient. Physical therapists can teach you how to walk in a way that opens up the spinal canal, which can help ease pressure on your nerves.
  • Steroid injections:Injecting corticosteroids near the space in the spine where nerve roots are being pinched or where worn areas of bone rub together can help reduce inflammation, pain and irritation. However, only a limited number of injections are usually given (typically three or four injections per year) because corticosteroids can weaken bones and nearby tissue over time.
  • Decompression procedure: This outpatient procedure, also known as percutaneous image-guided lumbar decompression (PILD), specifically treats lumbar spinal stenosis caused by a thickening of a specific ligament (ligamentum flavum) in the back of the spinal column. It is performed through a tiny incision and requires no general anesthesia and no stitches. The procedure is guided by an X-ray and a contrast agent that is injected during the procedure. The surgeon uses special tools to remove a section of the thickened ligament, which frees up space within the spinal canal, reducing compression on nerve roots. Some of the advantages of this procedure are that the bony architecture of the spine is left intact and there is little disruption in the mechanics of the spine so people recovery quickly. People usually go home a couple hours after the procedure and begin walking and/or physical therapy soon thereafter. Compared with before the procedure, you will be able to walk and stand for longer periods of time and experience less numbness, tingling and muscle weakness.

When is spinal stenosis surgery considered?

Because of the complexity of spinal stenosis and the delicate nature of the spine, surgery is usually considered when all other treatment options have failed. Fortunately, most people who have spinal stenosis don’t need surgery. However, talk with your healthcare provider about surgical options when:

  • Your symptoms are intolerable, you no longer have the quality of life you desire and you can’t do or enjoy everyday life activities.
  • Your pain is caused by pressure on the spinal cord.
  • Walking and maintaining your balance has become difficult.
  • You have lost bowel or bladder control or have sexual function problems.

What are the surgical treatments for spinal stenosis?

Surgery options involve removing portions of bone, bony growths on facet joints or disks that are crowding the spinal canal and pinching spinal nerves.

Types of spine surgery include:

Laminectomy (decompression surgery): The most common type of surgery for this condition, laminectomy involves removing the lamina, which is a portion of the vertebra. Some ligaments and bone spurs may also be removed. The procedure makes room for the spinal cord and nerves, relieving your symptoms.

In a laminectomy, the lamina portion of the vertebral bone is removed.

Laminotomy: This is a partial laminectomy. In this procedure, only a small part of the lamina is removed – the area causing the most pressure on the nerve.

Laminoplasty: In this procedure, performed in the neck (cervical) area only, part of the lamina is removed to provide more canal space and metal plates and screws create a hinged bridge across the area where bone was removed.

Foraminotomy: The foramen is the area in the vertebrae where the nerve roots exit. The procedure involves removing bone or tissue this area to provide more space for the nerve roots.

Interspinous process spaces: This is a minimally invasive surgery for some people with lumbar spinal stenosis. Spacers are inserted between the bones that extends off the back of each vertebrae called the spinous processes. The spacers help keep the vertebrae apart creating more space for nerves. The procedure is performed under local anesthesia and involves removing part of the lamina.

Spinal fusion: This procedure is considered if you have radiating nerve pain from spinal stenosis, your spine is not stable and you have not been helped with other methods. Spinal fusion surgery permanently joins (fuses) two vertebrae together. A laminectomy is usually performed first and bone removed during this procedure is used to create a bridge between two vertebrae, which stimulates new bone growth. The vertebrae are held together with screws, rods, hooks or wires until the vertebrae heal and grow together. The healing process takes six months to one year.

Is spinal surgery safe? What are the risks of surgery for spinal stenosis?

All surgeries have the risks of infection, bleeding, blood clots and reaction to anesthesia. Additional risks from surgery for spinal stenosis include:

  • Nerve injury.
  • Tear in the membrane that covers the nerve or spinal cord.
  • Failure of the bone to heal after surgery.
  • Failure of the metal plates, screws and other fasteners.
  • Need for additional surgery.
  • No relief of symptoms/return of symptoms.

How do I prepare for spinal stenosis surgery?

To prepare for spine surgery, quit smoking if you smoke and exercise on a regular basis (after checking with your healthcare provider first) to speed your recovery time. Ask your provider if you need to stop taking any non-essential medications, supplements or herbal remedies that you may be taking that could react with anesthesia. Also, never hesitate to ask your healthcare team any questions you may have or discuss any concerns.

What happens after spinal surgery?

If you’ve had a laminectomy, you may be in the hospital for a day or two. If you’ve had spinal fusion, you may have a three- to five-day hospital stay. If you’re older, you may be transferred to a rehabilitation facility to receive additional care before going home.

You will be given pain medications and/or NSAIDs to reduce pain and swelling. You may be given a brace or corset to wear for comfort. You will likely be encouraged to get up and walk as soon as possible. Your healthcare provider or physical therapist will recommend a light form of exercise right after spinal surgery to insure that your back does not stiffen and to reduce swelling. Your physical therapist will develop an individualized exercise plan to stretch and strengthen muscles to support your back and stabilize your spine.

Taking hot showers and using hot compresses may help alleviate pain. Additionally, using an ice pack may ease pain before and after exercise.

How long is the recovery period after spinal stenosis surgery?

Full recovery after surgery for spinal stenosis and return to normal activities typically takes three months and possibly longer for spinal fusion, depending partially on the complexity of your surgery and your progress in rehabilitation.

When can I return to work after spinal surgery?

If you’ve had a laminectomy, you will likely be able to go back to work at a desk job within a few days of returning home. If you’ve had spinal fusion, you’ll likely be able to return to work a few weeks after your surgery.

If you've been taking a muscle relaxant for an extended period, don't abruptly stop taking it one day. Doing so may set you up for some unpleasant withdrawal symptoms, such as nausea, vomiting, and trouble sleeping. When these drugs need to be discontinued, doctors typically taper the dose gradually before stopping the medicine.

It's good to keep in mind that muscle relaxants are just one part of pain control for your back problem. To keep back pain from returning, your doctor may recommend other treatments, such as physical therapy and exercise, ergonomic changes at work, and/or epidural steroid injections.

Erector Spinae Function

Erector spinae function is to stabilize the spine and allow us to make various types of movements that involve the spine. Where each muscle originates and attaches determines the range and direction of movement.

Other muscles of the back also help us to rotate, flex, and extend. Although the erector spinae are often called the deep back muscles, they are not the deepest. This is why you may see them labeled as intermediate muscles in anatomy books. The deeper muscle layer that lies underneath the erector spinae is a separate muscle group – the transversospinales muscles. They are mentioned in this article as they also play a part in movement but are definitely not part of the erector spinae muscle group.

The intermediate iliocostalis, intermediate spinalis, and intermediate longissimus muscles of the erector spinae (as they are also called) extend and lift the vertebral column to provide support. By separating the individual vertebrae they provide an extra layer of protection, keeping the small bones slightly apart and relieving pressure on the cartilage discs. One of the reasons we get smaller as we age is because of the thinning and stretching of these muscles – weaker, less dense bones and less distance between the vertebrae squashes the cartilage discs between them. If the erector spinae were in perfect condition throughout the aging process they would keep us closer to our original height.

The erector spinae also enable lateral flexion (bending sideways) and rotation of the back. Unilateral (one-sided) contraction of the erector spinae group causes the same side of the body to flex (ipsilateral flexion) or rotate, while bilateral contraction straightens or extends a portion of the spine. Pure erector spinae action is limited to flexion, rotation, and extension.

The erector spinae group contains three muscles than run either side of the spine. This means each muscle has a parallel partner connected by tendons – we can almost say we have two iliocostalis, two longissimus, and two spinalis muscles, although these are seen as single muscles.

Because this muscle group shares common tendons and nerve pathways and have a similar function they are grouped together under the umbrella term of erector spinae. Longissimus, spinalis, and iliocostalis muscles are all innervated by the spinal nerves and attach to shared areas of tendon at the vertebrae, sacrum, iliac crest, and sacroiliac and supraspinous ligaments. You can see where the supraspinous ligament covers the vertebrae in the image below.

Muscle location depends on where each muscle starts (its origin) and stops (its insertion site). The origin of any muscle refers to its attachment site to a part of the body that does not move the insertion point of a muscle tells us where the muscle causes movement by pulling a non-fixed part of the anatomy in the direction of the origin. This happens when the muscle contracts. That means that when you know the points of origin and insertion, you also know the direction of that muscle’s movement. As the spine consists of lots of small bones, there are also lots of erector spinae insertions.

Erector Spinae: Iliocostal Muscle

The musculus iliocostalis or iliocostal muscle is divided into the iliocostalis cervicis, iliocostalis thoracis, and iliocostalis lumborum. This might seem like a lot of tough Latin names but you only need to remember them once – cervicis relates to the cervical spine of the neck, thoracis to the vertebrae of the thorax, and lumborum to the lumbar spine or lower back. The neck part of the iliocostal muscle has its origins at the angles (curves) of the third to sixth ribs. Its insertion points are at the transverse processes of the fourth, fifth, and sixth cervical vertebrae. Transverse processes are located at either side of the spinous process (the part you can feel) of each vertebra. Of course, you don’t need to know the origin and insertions of each muscle, but when you picture them in your head, this information tells you that when the iliocostalis cervicis contracts, it brings the top of the neck (insertion) towards the upper ribs (origin).

The thoracic section of the iliocostalis muscle originates at the angles (curves) of the seventh to twelfth ribs and inserts into the upper ribs (numbers one to six) and the transverse process of the seventh (lowest) cervical vertebra. The picture below shows how many vertebrae are associated with the cervical, thoracic, and lumbar spine. You can also see the transverse processes of the individual vertebrae sticking out to either side. So this muscle, whenever it contracts, pulls the upper ribs slightly downwards. This assists in a minor way with breathing in and out, but mainly allows us to bend forwards (forward flexion).

The lumbar part of the iliocostal muscle (iliocostalis lumborum) originates at the sacrum and iliac crest and has insertion points at the angles (curves) of ribs five through to twelve, and the transverse processes of L1 to L4. So you know that this also allows a downward movement of the back and lower ribs towards the pelvis.

But the iliocostal muscle does not work alone – it is only part of the erector spinae group and needs its partners to be effective – the longissimus and spinalis muscles.

Erector Spinae: Longissimus Muscle

The longissimus muscle is the largest of the three erector spinae. It runs from the shared tendon of the lower back all the way up to the skull. It is, in fact, the longest muscle of the human body – and of most vertebrates – but with a name like longissimus, that’s not surprising.

Again, we can split the spine into different sections. The only difference is that we add the skull – or rather a bony attachment point of the skull called the mastoid process – to give us the name for the highest point of the longissimus muscle – the longissimus capitis. Capitis means head. This part is followed by the longissimus cervicis, thoracis and lumborum. However, because the thoracic and lumbar parts act similarly they are usually grouped together as the longissimus thoracis et (and) lumborum.

The longissimus capitis originates at the transverse processes of C4 to T5 and insert at the mastoid process of the skull. Sometimes called the trachelomastoid muscle, it allows head extension (straightening), flexion, and rotation. The longissimus cervicis (neck) originates at T1 to T5 and inserts at the second to the sixth cervical vertebrae. Those neck rotating exercises you do when you have sat at the computer too long? They involve a lot of longissimus cervicis work! Finally, the longissimus thoracis (et lumborum) origins at L1 to L5 and various bones of the pelvis and inserts into all of the thoracic vertebrae, the angles of the seventh to twelfth ribs, and L1 to L5. If you can keep a hula-hoop going, you have great lower longissimus muscles!

Erector Spinae: Spinalis Muscle

The spinalis muscle runs closest to the spine and is split into the spinalis capitis, spinalis cervicis, and spinalis thoracis. It is not as long as the longissimus so does not have a lumbar area.

The origins of the spinalis capitis are the spinous processes (the sticking out bits you can feel) of vertebrae C7 to T1. These insert to the middle of the occipital bone at the back of the skull – so we know this top part pulls the head back. Spinalis cervicis origins are also at C7 to T1 but these insert into C2 and C3, bringing the very top of the spine towards the thorax. Finally, spinalis thoracis – with origins at T11 to L2 – brings the spinous processes of T2 to T8 towards the lower back.

Here's How Ejaculation Actually Works

Ejaculation may feel like a glorious mess, as uncontrollable as an avalanche or a runaway train. In reality, it’s a tightly choreographed court dance: integrating three different branches of the nervous system, triggering cascades of contractions in smooth and striated muscles, all accompanied by the electrical storm of orgasm. Here’s how it works.

Sexual Feedback

Ejaculation is the endpoint of a process that begins with a touch. Skin covering the shaft and glans of the penis is filled with nerve endings sensitive to pressure and vibration. Stroking that skin sends signals to the brain that say ‘sexytime!”

The brain bundles those signals into the gestalt of information that it’s getting from other parts of the body: eyes, nose, imagination, and if sexual arousal develops, it responds by making that penile skin even more sensitive to touch. More touching further increases sensitivity, in a positive feedback loop that can build to a show-stopping involuntary eruption.

When enough stimulation trips arousal over into orgasm, it also triggers a storm of activity in the three ejaculatory centers deep in the brain. These areas, in the hypothalamus and the midbrain, fire off a pattern of impulses to coordinate the release of sperm from the testes, the creation of semen, and tie the final contractions tossing semen out of the body to the feelings of orgasm.

Loading the Charge

Before the spurting can begin, sperm need to be brought out of storage and put in position. And despite the tails, they can’t yet swim for themselves .

Instead, smooth muscles in the walls of male reproductive organs contract in a coordinated wave. The conveyor-belt like movement takes concentrated masses of sperm from the epididymis where they matured and dumps them into the urethra at the base of the penis. Along the way, they pass by a series of glands (like the seminal vesicles and the prostate) which each squeeze out specialized fluids that dilute the sperm and create the complex goo we call semen.

Semen accumulates at the back end of the penis, inside the base of an erectile structure called the corpus spongiosum (or in older papers, the corpus cavernosum urethrae). The corpus spongiosum is the odd man out of the three erectile structures inside the penis: unlike the two erection-producing corpora cavernosa that run alongside it, the corpus spongiosum is softer and flares at its tip to form the glans. Its base also swells slightly, forming a structure called the urethral bulb.

The urethra plunges into the middle of the bulb in a sort of turducken of sexual tissues: urethra at the center, erectile tissue surrounding it, all wrapped in layers of muscle. As semen fills the urethra, pressure starts to build in the bulb. The muscular conveyor belt from the reproductive ducts keeps pushing more fluid forward, and the bladder prevents back-flow by sealing its opening into the urethra. (The fact that the bladder closes up shop is also why urine doesn’t spurt out at orgasm.)

With nowhere else to go, the semen inflates the urethral bulb like a water balloon. As the bulb swells to 2-3 times its normal diameter, it adds “I’m full” signals to the erotic mix.

The whole process–called emission–has taken about 3 seconds, and it’s been paired with a growing feeling of inevitability. Now we’re ready for the big finish.

Past the Point of No Return

This is the point at which wads are shot, loads are dropped, rocks are shot off. The euphemisms are telling: the main event–expulsion–is completely involuntary, a reflex run by the spinal cord, no brain input needed. And once it starts, it can’t be stopped.

The signal that tells male genitals the big moment has arrived comes from a group of neurons near the base of the spinal cord called Onuf’s nucleus. Once triggered, their signals take control of the muscles at the base of the penis and touch off a series of strong involuntary contractions.

One of the muscles in question, the bulbospongiosus (also called the bulbocavernosus in old texts), surrounds the entire urethral bulb and the rear of the corpus spongiosum. A second surrounds the urethra proper. Together, they form a muscular pump that can throw semen out of the body with a surprising amount of force.

When the right signal arrives, the pumping starts. Both muscles contract together rhythmically, raising the pressure in the urethral bulb in pulses and pushing semen through the urethra in spurts. Each high pressure push is followed by a short period of relaxation which lets the urethral bulb refill with semen. Sensory feedback from the pulsed contractions tie into (and may intensify) the brain’s orgasmic cascades.

The pressure change in the urethral bulb is substantial: each contraction also creates sympathetic pressure peaks in the blood inside the erect corpus spongiosum. The first few squeezes are so forceful that semen doesn’t simply travel the 5 to 6 inches of the penile urethra to its opening in the glans–the first few spurts can fly one to two feet through the air beyond it.

The muscles follow up the first three or four strong contractions with several seconds of slower, weaker pulses, moving between 2 to 5 milliliters of semen to the outside world. Once that’s done, at least for a while, all that’s left is the mopping up.

Why Are They So Important?

Long story short, they hold us up! That means we need them now more than ever!

With sedentary lifestyles becoming more common and technology pulling our heads and spines forward, our erectors are being chronically lengthened. The result is a weakness in these muscles. The pain you’re feeling often comes from weaknesses and overstretching of these muscles.

The weakness in a muscle or muscle group results in feelings of tightness. This is why we always feel the need to “stretch” them. But remember that stretching is a short term relief strategy that will only push your problems further down the road. You must strengthen them!

Lost Posture: Why Some Indigenous Cultures May Not Have Back Pain

Primal posture: Ubong tribesmen in Borneo (right) display the perfect J-shaped spines. A woman in Burkina Faso (left) holds her baby so that his spine stays straight. The center image shows the S-shaped spine drawn in a modern anatomy book (Fig. I) and the J-shaped spine (Fig. II) drawn in the 1897 anatomy book Traite d'Anatomie Humaine. Courtesy of Esther Gokhale and Ian Mackenzie/Nomads of the Dawn hide caption

Primal posture: Ubong tribesmen in Borneo (right) display the perfect J-shaped spines. A woman in Burkina Faso (left) holds her baby so that his spine stays straight. The center image shows the S-shaped spine drawn in a modern anatomy book (Fig. I) and the J-shaped spine (Fig. II) drawn in the 1897 anatomy book Traite d'Anatomie Humaine.

Courtesy of Esther Gokhale and Ian Mackenzie/Nomads of the Dawn

We are marking a milestone, 50 years of NPR, with a look back at stories from the archive.

Editor's note, June 10: We have added an acknowledgement of several sources that Esther Gokhale used while developing her theories on back pain. These include physiotherapy methods, such as the Alexander Technique and the Feldenkrais Method, and the work of anthropologist Noelle Perez-Christiaens.

Back pain is a tricky beast. Most Americans will at some point have a problem with their backs. And for an unlucky third, treatments won't work, and the problem will become chronic.

Many ancient statues, such as this one from Greece, display a J-shaped spine. The statue's back is nearly flat until the bottom, where it curves so the buttocks are behind the spine. Courtesy of Esther Gokhale/Gerard Mackworth-Young hide caption

Many ancient statues, such as this one from Greece, display a J-shaped spine. The statue's back is nearly flat until the bottom, where it curves so the buttocks are behind the spine.

Courtesy of Esther Gokhale/Gerard Mackworth-Young

Believe it or not, there are a few cultures in the world where back pain hardly exists. One indigenous tribe in central India reported essentially none. And the discs in their backs showed little signs of degeneration as people aged.

An acupuncturist in Palo Alto, Calif., thinks she has figured out why. She has traveled around the world studying cultures with low rates of back pain — how they stand, sit and walk. Now she's sharing their secrets with back pain sufferers across the U.S.

About two decades ago, Esther Gokhale started to struggle with her own back after she had her first child. "I had excruciating pain. I couldn't sleep at night," she says. "I was walking around the block every two hours. I was just crippled."

Gokhale had a herniated disc. Eventually she had surgery to fix it. But a year later, it happened again. "They wanted to do another back surgery. You don't want to make a habit out of back surgery," she says.

This time around, Gokhale wanted to find a permanent fix for her back. And she wasn't convinced Western medicine could do that. So Gokhale started to think outside the box. She had an idea: "Go to populations where they don't have these huge problems and see what they're doing."

Esther Gokhale's Five Tips For Better Posture And Less Back Pain

Try these exercises while you're working at your desk, sitting at the dinner table or walking around, Esther Gokhale recommends.

1. Do a shoulder roll: Americans tend to scrunch their shoulders forward, so our arms are in front of our bodies. That's not how people in indigenous cultures carry their arms, Gokhale says. To fix that, gently pull your shoulders up, push them back and then let them drop — like a shoulder roll. Now your arms should dangle by your side, with your thumbs pointing out. "This is the way all your ancestors parked their shoulders," she says. "This is the natural architecture for our species."

2. Lengthen your spine: Adding extra length to your spine is easy, Gokhale says. Being careful not to arch your back, take a deep breath in and grow tall. Then maintain that height as you exhale. Repeat: Breathe in, grow even taller and maintain that new height as you exhale. "It takes some effort, but it really strengthens your abdominal muscles," Gokhale says.

3. Squeeze, squeeze your glute muscles when you walk: In many indigenous cultures, people squeeze their gluteus medius muscles every time they take a step. That's one reason they have such shapely buttocks muscles that support their lower backs. Gokhale says you can start developing the same type of derrière by tightening the buttocks muscles when you take each step. "The gluteus medius is the one you're after here. It's the one high up on your bum," Gokhale says. "It's the muscle that keeps you perky, at any age."

4. Don't put your chin up: Instead, add length to your neck by taking a lightweight object, like a bean bag or folded washcloth, and balance it on the top of your crown. Try to push your head against the object. "This will lengthen the back of your neck and allow your chin to angle down — not in an exaggerated way, but in a relaxed manner," Gokhale says.

5. Don't sit up straight! "That's just arching your back and getting you into all sorts of trouble," Gokhale says. Instead do a shoulder roll to open up the chest and take a deep breath to stretch and lengthen the spine.

[Added June 10] So Gokhale studied findings from anthropologists, such as Noelle Perez-Christiaens, who analyzed postures of indigenous populations. And she studied physiotherapy methods, such as the Alexander Technique and the Feldenkrais Method.

And the original post continues .

Then over the next decade, Gokhale went to cultures around the world that live far away from modern life. She went to the mountains in Ecuador, tiny fishing towns in Portugal and remote villages of West Africa.

"I went to villages where every kid under age 4 was crying because they were frightened to see somebody with white skin — they'd never seen a white person before," she says.

Gokhale took photos and videos of people who walked with water buckets on their heads, collected firewood or sat on the ground weaving, for hours.

"I have a picture in my book of these two women who spend seven to nine hours everyday, bent over, gathering water chestnuts," Gokhale says. "They're quite old. But the truth is they don't have a back pain."

She tried to figure out what all these different people had in common. The first thing that popped out was the shape of their spines. "They have this regal posture, and it's very compelling."

And it's quite different than American spines.

If you look at an American's spine from the side, or profile, it's shaped like the letter S. It curves at the top and then back again at the bottom.

But Gokhale didn't see those two big curves in people who don't have back pain. "That S shape is actually not natural," she says. "It's a J-shaped spine that you want."

In fact, if you look at drawings from Leonardo da Vinci — or a Gray's Anatomy book from 1901 — the spine isn't shaped like a sharp, curvy S. It's much flatter, all the way down the back. Then at the bottom, it curves to stick the buttocks out. So the spine looks more like the letter J.

"The J-shaped spine is what you see in Greek statues. It's what you see in young children. It's good design," Gokhale says.

So Gokhale worked to get her spine into the J shape. And gradually her back pain went away.

Healthy spines in the Western world: The J-shaped spine is often seen in photographs from the late 19th and early 20th centuries. Library of Congress hide caption

Healthy spines in the Western world: The J-shaped spine is often seen in photographs from the late 19th and early 20th centuries.

Then Gokhale realized she could help others. She developed a set of exercises, wrote a book and set up a studio in downtown Palo Alto.

Now her list of clients is impressive. She's helped YouTube CEO Susan Wojcicki and Matt Drudge of the Drudge Report. She has given classes at Google, Facebook and companies across the country. In Silicon Valley, she's known as the "posture guru."

Each year, doctors in the Bay Area refer hundreds of patients to Gokhale. One of them is Dr. Neeta Jain, an internist at the Palo Alto Medical Foundation. She puts Gokhale's method in the same category as Pilates and yoga for back pain. And it doesn't bother her that the method hasn't been tested in a clinical trial.

"If people are finding things that are helpful, and it's not causing any harm, then why do we have to wait for a trial?" Jain asked.

But there's still a big question looming here: Is Gokhale right? Have people in Western cultures somehow forgotten the right way to stand?

Scientists don't know yet, says Dr. Praveen Mummaneni, a neurosurgeon at the University of California, San Francisco's Spine Center. Nobody has done a study on traditional cultures to see why some have lower rates of back pain, he says. Nobody has even documented the shape of their spines.

"I'd like to go and take X-rays of indigenous populations and compare it to people in the Western world," Mummaneni says. "I think that would be helpful."

But there's a whole bunch of reasons why Americans' postures — and the shape of their spines — may be different than those of indigenous populations, he says. For starters, Americans tend to be much heavier.

"If you have a lot of fat built up in the belly, that could pull your weight forward," Mummaneni says. "That could curve the spine. And people who are thinner probably have less curvature" — and thus a spine shaped more like J than than an S.

Americans are also much less active than people in traditional cultures, Mummaneni says. "I think the sedentary lifestyle promotes a lack of muscle tone and a lack of postural stability because the muscles get weak."

Click here to subscribe to our weekly global health and development email. NPR hide caption

Everyone knows that weak abdominal muscles can cause back pain. In fact, Mummaneni says, stronger muscles might be the secret to Gokhale's success.

In other words, it's not that the J-shaped spine is the ideal one — or the healthiest. It's what goes into making the J-shaped spine that matters: "You have to use muscle strength to get your spine to look like a J shape," he says.

So Gokhale has somehow figured out a way to teach people to build up their core muscles without them even knowing it. "Yes, I think that's correct," Mummaneni says. "You're not going to be able to go from the S- to the J-shaped spine without having good core muscle strength. And I think that's key here."

So indigenous people around the world don't have a magic bullet for stopping back pain. They've just got beefy abdominal muscles, and their lifestyle helps to keep them that way, even as they age.