What Causes Low Back Pain?

One of my biggest pet peeves is when doctors and other medical practitioners don’t take the time to explain and educate their patients the basics of their anatomy and why their injury occurred (called the injury mechanism). Today, I want to briefly go over the anatomy of the low back and cover some of the most common injuries that can occur in this region.

The Spine

Your spine is not just a stack of bones. It’s a slightly curved “tower” of small bones called vertebrae, each one separated by a disc. These discs provide cushion (much like an air bag) for the vertebrae as they move. Each vertebra of your spine is connected to the other through small joints in the back called facets. These joints allow the spine to bend and twist. All together, the entire “tower” is held together by a number of different tissues (muscles, ligaments, joint capsules and fascia).

The Mechanism of Injury

So to the question ‘what causes low back pain?’ the simplest answer is that pain is the result of excessive stress or strain on the structures of your back. For the strength athlete these forces are often the result of cumulative micro-trauma due to three things:

1. Poor movement or technique
2. Excessive training loads (too much compression on the spine)
3. Poor training programming or periodization (not enough rest)

Every part of your body (from the small bones and joints to the large muscles that span across them) has a certain set amount of force or load it can tolerate before it fails and breaks. Athletes who are able to push themselves to the brink of this tipping point without going overboard often find massive success in improving their strength and performance. However, if that threshold is exceeded, injury occurs and pain sets in.

As we move throughout our day and also when we lift weights during our workouts, the spine is most efficient when in a neutral stacked position. A neutral positioned spine can also tolerate higher amounts of force. If our back constantly moves out of this ideal alignment during heavy lifts, micro-trauma can occur to your spine (such as deadlifting with an excessive rounded back or allowing excessive butt wink in a deep back squat). Micro trauma can also occur when the spine is compressed with too much load/force. Everyone has their own tipping point in terms of load tolerance of the spine. The tiny amounts of micro-trauma to your spine can eventually push the body’s tipping point over and lead to pain and intoralnce to load.⁵

While there may be one specific point in time at which the pain strikes (as Ryan from our previous story felt with the “pop” in his back during his last clean & jerk), the injury itself for most strength athletes is usually the result of something that has been building for some time. This means that while you may have “thrown your back out” bending over to tie your shoes or threw your back out when performing your last clean & jerk set, the cause of injury has actually been building up to that point.

Let’s now dive a little deeper into some of the most common forms of back injury sustained by strength athletes.

Disc Bulges and Herniation

What exactly is a disc bulge? When many in the medical field try to explain this injury they’ll use the analogy of the jelly donut.

Like a jelly donut, the discs of your spine have an inner gel-like center called the nucleus pulposus. If there is too much compression on the spine the vertebrae will be squeezed together and (like a donut being smashed between your hands) the gel will be forced out of the middle of the disc that lies between them.

However this analogy isn’t actually as good of a comparison as many think. Here’s why.

During any barbell training, there is a considerable amount of compression placed on the spine, a majority that comes from the muscles that surround the back. As you pull a barbell from the ground for example, the muscles that surround your spine tighten down to create enough stiffness to keep your spinal “tower” from buckling in two. The contraction of these muscles (along with the force of the weight being lifted) compresses the spinal column.

In between each vertebral bone lays a disc that contains a gel-like nucleus that is surrounded by many ring-like layers of a strong material called collagen. While you can easily push the inner jelly of a donut out of its center by smashing it with your hands, the collagen rings of your spinal discs that surround the nucleus are extremely tough (in fact collagen is actually the same kind of tissue as the ligaments and tendons that hold your body together). This is why a disc bulge is extremely rare when the spine is compressed in a neutral position (like when you squat or deadlift with good posture.^5,8,9

However, if the spine experiences a ton of compression while in a overly flexed position (like the athlete deadlifting a barbell with a collapsed back or excessive butt wink occurs at the bottom of a squat) the small collagen layers of the disc slowly begin to crack and break apart (this process is called delamination).^8,9,12 When this process happens over and over again, the inner gel of the disc is forced through these newly formed cracks in the surrounding collagen.^8,10,18 This seepage of the inner gel of the disc is called a bulge and if it’s severe enough it can lead to debilitating back pain and nerve irritation (causing pain to radiate down one or both legs).

Every athlete tolerates the forces of bending their spine differently.  This is why elite gymnasts are able to literally bend themselves in half over and over, yet a NFL lineman attempting the same movements would spell disaster. Depending on a number of factors (such as your anatomy, genetics, the amount of weight lifted, the degree of poor technique) your body may be more or less resilient to developing a disc bulge.^24,31 However, every spine has a breaking point and the quickest way to find it is to load your spine with a ton of compression (like lifting weights) and perform rep after rep with poor technique.

But what about elite powerlifters who deadlift with a rounded back?

Because lifting the most weight is the goal for competitive powerlifters, it is common to see some degree of lumbar and thoracic spine (mid back) rounding during max effort deadlifts.²⁸ This is more often seen in those who use a conventional style pulling technique versus a sumo style deadlift. However, there are some elite powerlifters who have been known to purposefully hunch or round their back.²⁷

But doesn’t this go against everything we just learned? Yes and no. To start, elite powerlifters who lift with this technique aren’t usually allowing their back to move into more flexion as the lift is pulled. They’re instead bracing or “locking-in” their spine with a slight bend and maintaining that degree of flexion during the deadlift. By not allowing any motion in this spine this position, they limit the extreme amount of compression that would be transferred to the spinal discs if it were to be moved into full flexion.^27,29 When combined with a proper training program, some athlete’s have likely been able to adapt to this position and remain injury free.

If adding compression to the spine when it’s out of neutral position places uneven forces on the spine that leads to a greater possibility of developing disc bulge, why would an athlete attempt to lift in this manner? The rational is that starting with a slightly rounded spine decreases the amount of force the low back extensor muscles need to generate in order to perform the movement. If you want to really go into the science of it, the rounded back shortens the moment arm between the shoulders and lower lumbar joints.²⁷ A shorter moment arm theoretically demands less from the body to lift the weight from the floor.

However, advice to start rounding your back to add a few more pounds to your deadlift must certainly be taken with extreme caution. While some can get away with technique, many will not adapt and will fall prey to a disc bulge injury. Therefore, you must weigh the risk and reward ratio of lifting with this technique.

Vertebral End-Plate Fracture

The vertebrae of your body aren’t just solid bone. If you sawed one in half you’d actually see a very intricate network of sponge-like struts that branch throughout and connect together called trabecular bone.²¹ This complex arrangement creates a stiff framework to support the bone, allowing it to bear weight and resist being crushed by compressive loads.¹⁹

Just like your muscles, the bones of your body can respond negatively or positively to the loads and frequency of loading it experiences during weight training. For example, lifting heavy weights with proper programming periodization causes your spine to adapt and the trabecular struts within the vertebrae bone to thicken over time.²¹ This is why research has shown elite powerlifters (who experience compressive forces on their spine of up to 16 times their bodyweight) to have some of the highest density vertebral bones ever seen in humans.^20,25-27

During this adaption process the spine will sometimes develop tiny micro-fractures. In the book ‘Gift of Injury’ renowned back expert Dr. Stuart McGill wrote that he has never seen an elite powerlifter who did not have evidence of a history of these micro-fractures in their spine.²³

Usually these fractures start at a layer of tissue that is part bone and cartilage and separates the vertebrae bone and the underlying disc called the end-plate. The end plate has two jobs. First, it has to be strong to handle compressive forces placed on the spine and prevent the inner gel of the disc from bulging into the above bone. Second, it must be porous or soft enough to allow nutrients and blood to flow to and from the disc below.

When there is a lot of compression applied to the spine, the end plate is stretched across the bone it covers (like someone spreading saran plastic wrapping across a bowl).²² Excessive compression can eventually overwhelm this plate and cause it (along with the underlying trabecular bone of the vertebrae) to crack.

If given time to adequately recover after over-loading the body during a heavy training cycle, the body can adapt and replace this micro-fracture with stronger bone. Think of this process like a callus developing on your hands to keep them stronger and more resilient to gripping the barbell. However, if there is insufficient recovery (like jumping back into another heavy training cycle without taking a de-load week or two) the pressure placed on the spine will accumulate and cause it to cross the tipping point. This is when these once small micro-fractures to turn into a big problem.^19,22

Facet Injury

Another reason someone can develop pain at the low back is an injury to the small joints on the backside of the spine called the facets.¹¹ In fact, some research studies have estimated that between 15% and 40% of chronic back pain is due to a facet joint injury.¹³

So how does an injury occur here?

Much like a glove that fits tightly over your hand, each one of your facet joints is surrounded by a strong capsule. This capsule is highly innervated, meaning it has a ton of nerves that run through it that help sense spine position, movement and pain.¹³ Much like the disc bulge, an injury to the facet joint is not often caused by one specific event but instead can be traced back to repetitive strain or micro trauma over time.¹⁷

The interesting thing about facet joints is that they can change in shape depending on the level they are found on the spine. Some facet joints can help create and limit excessive rotation of the spine, while others are set up to do the same for backward and forward bending.

For this reason, these joints can be injured during a number of different movements. For example, when the spine is hyperextended (like the athlete who over arches their back while pressing a barbell over their head) a large amount of pressure is shifted to these small joints of the lower spine (lumbar spine), which stretches the surrounding capsule.¹³ If the body cycles too often into this position it can lead to irritation of these joints and the surrounding capsules leading to pain and eventual arthritis.

Research has also shown that facet joint irritation can be caused by either bending or extension of the spine combined with rotation.¹⁷ Lets take for example a weightlifter who has uneven hip mobility. If he or she moves under the bar to catch a heavy clean and the back rounds under the excessive load, a mobility asymmetry in the hips may lead to a small twisting in the pelvis resulting in excessive stretch to the capsule of his lower facet joints. If this side-to-side difference isn’t addressed and fixed, over time the small technique problem that occurs may lead to irritation of a facet capsule/joint and eventual pain.

Spondylolysis

Another one of the possible injuries an athlete can sustain to the structures on the backside of the spine is spondylolysis. Historically, this is one of the most serious back injuries for strength athletes. Spondylolysis is a stress fracture of the spine. It occurs at a very small part of the vertebrae called the pars interarticularis (right next to the facet joint).

Mechanically, this area absorbs a significant amount of force, especially if the low back is in an extended or arched position (called lumbar lordosis). Much like the injury to the facet joint, repetitive loading of this area with an extended spine over time is thought to be the main cause of developing this injury. If left unchecked, this stress fracture can lead to the much more serious problem, spondylolisthesis (anterior sliding of the spinal vertebra).

This injury was once thought to be very prevalent in strength athletes. There are a number of research articles that suggested weightlifters and powerlifters specifically were at high risk for sustaining this fracture.

For example, after following 26 Japanese weightlifters for several years, researchers found 24 of 26 to have recurrent back pain. Eight (31%) of these athletes were found to have spondylolysis.¹ Another group of researchers studied 27 weightlifters and 20 powerlifters and found twenty one (44%) to have spondylolysis.² No significant difference was found between the weightlifters and powerlifters in this study.

However, there are a few things to take into consideration when looking at these numbers. First, research has shown that spondylolysis is strongly influenced by your genetics.³ This means some of us are unfortunately pre-disposed to having this injury and the sport itself isn’t necessarily the main culprit.

Second, every one of the studies that observed this injury among weightlifters did so before 1972. Before this time, the clean and press was an official lift used in competition. The pressing portion of this lift was usually performed with considerable hyperextension of the lower back. Performing this repeated motion while pushing tremendous weight likely led to the high percentage of documented spondylolysis injuries.⁴

Nevertheless, while the amount of strength athletes that sustain this injury may not be as widespread as previously reported in research, this spinal stress fracture can still occur if you repeatedly arch your low back and place it in an extended position while performing any exercise (such as a squat, push press or even a kettle bell swing).

Nerve Pain

Do you have a stinging or burning pain that shoots down your legs? What about numbness in your thigh or feet? These symptoms are caused by irritation of nerves.

Imagine the spinal cord that runs down your back as a major highway. Much like the small roads that branch off a highway, you have many nerves that exit the spinal column through tiny openings and travel throughout your entire body providing constant information (like the sensation of pain, touch or movement) back to your central control center for processing.

When there is an injury in the spine (from a bulging disc or degrading arthritis in the facet joints of the vertebrae) the nerves that run close by can be pinched. When this happens, pain is sent shooting down the entire length of the nerve.^14,15

If you have experienced pain that radiates down the backside of your thigh, it is likely sciatica (irritation of the sciatic nerve). This pain can be caused by a disc bulge in the spine or an entrapment of the nerve by the piriformis much lower at the hip. Pain that is felt traveling down the front side of the thigh is caused by a different nerve called your femoral nerve.

Muscle Pain 

Have you ever heard of the term “lumbar muscular sprain or strain?” That’s often one of the most common diagnoses given from medical doctors for anyone who has an acute episode of low back pain. However, some experts are starting to agree that this is rarely the main cause of the injury.^6,7

When someone develops an injury to his or her back (due to a disc bulge, facet irritation, etc.) it creates a chemical reaction called inflammation. This leads to a secondary contraction or spasm of the muscles that surround the injured site (likely as a compensation reaction of our body to stabilize around the injury).^16,17

While a muscle strain injury may be common else where in your body (like the hamstrings), the sensation of pain and tenderness in the muscles of your low back are likely only referring pain from the real problem that lies much deeper.^6,7

Keep Your Head Up

As you have read by now, there are many different ways in which the spine and its surrounding tissues can be damaged during weight training. While each injury is very different, you may have noticed a similar underlying theme behind them all. The quality of your technique and the manner you load your body during training will always be the most important factors in determining whether or not your body adapts and progresses or fails to adapt and ultimately finds injury.

If you have found yourself to have one of the above injuries, don’t hang your head. There is hope! While you may currently be in pain, the good news is that your spine can often heal from these injuries we just discussed (and without surgery!).

Next week we’ll start step one of fixing your injury by diving into how to screen your low back. You’ll find that an efficient screening process will be more valuable than spending thousands on an expensive MRI.

Until next time,

With

References

1. Katani PT, Ichikawa N, Wakabayashi W, et al. Studies of spondylolysis found among weightlifters. Br J Sports Med. 1971 Nov; 6(1):4-8
2. Dangles CJ & Spencer DL. Spondylolysis in competitive weightlifters. J Sports Med. 1987;15:634-635
3. Yochum TR & Rowe LJ. The natural history of spondylolysis and spondylolysthesis: Essentials of Skeletal Radiology. T.R. Yochum and L.J. Rose, eds. Baltimore: Williams & Wilkins. 1987;243-272
4. Stone MH, Fry AC, Ritchie M, et al. Injury potential and safety aspects of weightlifting movements. Strength and Conditioning. 1994 June; 15(3):15-21
5. McGill SM. The biomechanics of low back injury: implications on current practice in industry and the clinic. J Biomechanics. 1997;30(5):465-475
6. McGill, SM. Back Mechanic: The step by step McGill Method to fix back pain. Backfitpro Inc. 2015
7. Frontera WR, Silver JK, Rizzo TD Jr. Essentials of Physical Medicine and Rehabilitation: Musculoskeletal Disorders, Pain and Rehabilitation. 3^rd Saunders. 2014
8. Wade KR, Robertson PA, Thambyah A, Broom ND. How healthy discs herniate: a biomechanical and microstructural study investigating the combined effects of compression rate and flexion. Spine. 2017;39(13):1018-28
9. Callaghan JP & McGill SM. Intervertebral disc herniation: studies on a porcine model exposed to highly repetitive flexion/extension motion with compressive force. Clin Biomech. 2001;16(1): 28-37
10. Claudio T, Drake JD, Callaghan JP, McGill SM. Progressive disc herniation: an investigation of the mechanism using radiologic, histochemical, and microscopic dissection techniques on a porcine model. Spine. 2007;32(35):2869-74
11. Manchikanti L, Hirsch JA, Falco FJ, Boswell MV. Management of lumbar zygapophysial (facet) joint pain. World J Orthop. 2016;7(5):315-37
12. Gunning JL, Callaghan JP, McGill SM. Spinal posture and prior loading history modulate compressive strength and type of failure in the spine: a biomechanical study using a porcine cervical spine model. Clin Biomech. 2001;16:471-80
13. Dreyer SJ & Dreyfuss PH. Low back pain and the zygapophysial (facet) joints. Arch Phys Med Rehabil. 1996;77:290-300
14. Reynolds AF, Weinstein PR, Wachter RD. Lumbar monoradiculopathy due to unilateral facet hypertrophy. Neurosurgery. 1982;10(4):480-6
15. Wilde GP, Szypryt ET, Mulholland RC. Unilateral lumbar facet hypertrophy causing nerve root irritation. Ann R Coll Surg Engl. 1988;70:307-10
16. Indahl A, Kaigle A, Reikeras O, Holm S. Electromyographic response of the porcine multifidus musculature after nerve stimulation. Spine. 1995;20(24):2652-8
17. Cohen SP & Raja SN. Pathogenesis, diagnosis, and treatment of lumbar zygapophysial (facet) joint pain. Anesthesiology. 2007;106:591-614
18. Marshall LW & McGill SM. The role of axial torque in disc herniation. Clin Biomech. 2010;25(1):6-9
19. van Dieën JH, Weinans H, Toussaint HM. Fractures of the lumbar vertebral endplate in the etiology of low back pain: a hypothesis on the causative role of spinal compression in aspecific low back pain. Med Hypotheses. 1999; 53(3):246-52
20. Dickerman RD, Pertusi R, Smith GH. The upper range of lumbar spine bone mineral density? An examination of the current world record holder in the squat lift. Int J Sports Med. 2000;21(7):469-70
21. Oftadeh R, Perez-Viloria M, Villa-Camacho JC, Vaziri A, Nazarian A. Biomechanics and mechanobiology of trabecular bone: a review. J Biomech Eng. 2015;137(1):0108021-0180215
22. Lotz JC, Fields AJ, Liebenberg EC. The role of the vertebral end plate in low back pain. Global Spine J. 2013;3(3):153-164
23. McGill SM, Carroll B. Gift Of Injury. Backfitpro Inc. 2017
24. McGill SM. Spine flexion exercise: myths, truths and issues affecting health and performance. Backfitpro.com. Web. March 10, 2018.
25. Granhed H, Jonson R Hansson T. The loads on the lumbar spine during extreme weight lifting. Spine. 1987;12(2):146-9
26. Walters PH, Jezequel JJ, Grove MB. Case study: bone mineral density of two elite senior female powerlifters. J Strength Cond Res. 2012;26(3):867-72
27. Cholewicki J, McGill SM, Norman RW. Lumbar spine loads during the lifting of extremely heavy weights. Med Sci Sports Exerc. 1991;23(10):1179-86
28. Spencer K & Croiss M. The effect of increased loading on powerlifting movement form during the squat and deadlift. J Hum Sport Exerc. 2015;10(3):764-774
29. Cholewicki J & McGill SM. Lumbar posterior ligament involvement during extremely heavy lifts estimated from fluoroscopic measurements. J Biomech. 1992;25(2):17-28
30. Yates JP, Giangregorio L, McGill SM. The influence of intervertebral disc shape on the pathway of posterior/posterolateral partial herniation. Spine. 2010;35(7):734-739