Crunching Your Way to Back Pain
By Bill Bolster / October 10, 2016
Contrary to popular belief, crunches are not the ultimate core exercise. In fact, every variation of the crunch is potentially damaging movement on the low back. I know this may come as a bit of a surprise for you, especially because “ab strengthening” exercises like these are littered throughout magazines, social media, and the latest boot camps every day. It’s evident the professionals (I’m using those terms loosely) recommending these exercises don’t have the basic understanding of engineering or anatomy, and considering that the musculoskeletal system is a series of levers and pulleys propelling our movement, that’s relatively important.
Despite what you may hear on the radio, Ankylosing Spondylitis is probably not your source of low back pain. Inflammatory autoimmune conditions, degenerative disease, or traumatic injury are an explanation for some of the chronic back pain cases seen throughout the health industry, but they are an anomaly. Poor movement and general ignorance of what we’re subjecting our spines to is a far greater likelihood of our impending low back pain and injury.
Complete anatomy of the spine is above the scope of this article, but there’s a relatively simple analogy that can be made to demonstrate how the spine withstands the forces we subject it to daily.
Think of the spine as a fishing pole; butt end of the pole on the ground with the tip up in the air. Placing your palm on the tip of the pole, and exerting even the slightest downward force will cause the pole to bend and buckle in different directions. Much like the free standing fishing pole, an osteoligamentous lumbar spine (no muscular attachments) bends and buckles under only 20 pounds of pressure, and yet somehow it’s able to support not only our body weight, but large external loads every day.
Imagine that same fishing pole, but now add hundreds of guy wires (muscular attachments), from the base of the pole to the top. These guy wires extend out and attach to the ground, under tension, stabilizing the entire fishing pole (spine). The pole can now resist the urge to bend and buckle, even under large compressive loads because of the added stability throughout its entire structure, much like how the spine uses its muscular attachments.
However, the spine’s greatest asset can be its downfall. The muscular forces that protect the spine can also destroy it, if not used properly. It’s important to understand that every tissue in the musculoskeletal system has a point at which it will fail, and injury occurs. Injury can occur during a single, culminating event (i.e. an ACL rupture), or repetitive stress (micro-trauma) over an extended period of time, the latter being most consistent with back injury.
Unfortunately, crunches are a demanding task on our lumbar spines. With each repetition of a crunch we impose about 740 pounds of pressure on the lumbar spine, the daily limit for low back compression set by NIOSH (National Institute of Occupational Health and Safety). That means with every crunch we compress our spines to the recommended daily limit. As we continue this movement, repetition after repetition, the tissue (disc) begins to fatigue, increasing the likelihood of tissue failure. Without the proper conditioning of the tissues or adequate time to heal, even lifting a light load (bending over to pick up your shoes, laundry, a child, etc.) can lead to injury, and pain.
Repetitive poor movements compromise the integrity of our tissues; it’s as simple as that. Compromises in a joint’s freedom will result in misplaced forces, and improper placement of forces from poor joint mobility comes with an increased likelihood of injury. The key word being movement, although this article focuses primarily on crunches, the same information can be inferred for any load-bearing movement performed. Individuals who are consistently lifting objects off the ground, or spend an inordinate amount of time in poor postures will presumably be putting similar stresses on the spine.
I don’t mean to give the impression that we should never flex our spine, of course we should. In order for a joint to be healthy it needs to explore all ranges of motion, the spine is no different in this sense. That being said, just because we have the capability to perform a particular movement does not mean it should be done haphazardly. We have to train and prepare our bodies for said movement.
When it comes to training the core, it’s not strength we lack, but endurance. This is evident by people often complaining of fatigue not in their abdomen, but rather the front of their hips as they are performing crunch variations. The core musculature fatigues after just a few repetitions and we then rely on our hip flexors to act inefficiently, pulling the trunk closer to the thighs. Not only is this a very demanding task for the hip flexors to perform, this is the mechanism producing most of the compressive force on the lumbar spine. Rather than “strengthening” the core by doing crunches, this repeated flexion exercise actually perpetuates the injury cycle and causes repeated damage to the low back. This mechanism often leads low back patients into a chronic pain state. Do yourself, and your back, a favor by building endurance throughout the core musculature before anything else. Plank variations, bird-dog progressions, side bridging, along with chops and lifts are great ways to begin building endurance through the core musculature while keeping the spine in a rigid, neutral position- an important capability in reducing load on the spine and rehabilitating an injury.
It’s important to understand I am not condemning crunches, their variations, or flexion based abdominal exercises altogether. However, these exercises should never be the go-to exercises for ill prepared and novice trainees. Those training for optimum performance will undoubtedly receive strength benefit as a result of doing crunches, but realize it will come with an increased risk. It’s also important to understand these individuals likely built the prerequisite endurance necessary to receive said strength benefits, have proper movement patterns, and adequate training experience. That being said, crunch variations should never be the cornerstone to a core routine, and must be performed cautiously. Those training for everyday health would be wise to forfeit crunches altogether.
-Dr. Bill Bolster DC, CES PES