By Raquel Lannes-Sherrill, MA, CSCS
The “crunch,” taught for decades, has been viewed as a staple of abdominal training. Should it be? A number of experts have questioned the effectiveness and more importantly, the clinical consequences of doing crunches and sit-ups. Research conducted by Stuart McGill, PhD, and Shirley Sahrmann, PhD, PT, FAPTA, indicates other abdominal training is both safer and more effective.
McGill is a world renowned authority of spine biomechanics who has researched the spine for over 32 years. In a nutshell, he is the author of several books relating to low back pain, enhancing performance, and reducing the risk of injury through re-patterning poor movement patterns and restoring function. McGill is not in the business of seeing the average low back pain patient. Patients from the disabled to elite athletes are referred to McGill only for special cases of back pain. As McGill explains, he sees the “basket case” of bad backs when conventional therapies have failed.
McGill is no fan of sit-ups, crunches, or any of their variations. McGill has been misquoted saying, “There are only so many bends or a ‘fatigue life’ in your spinal disks.” This quote has been taken out of context. “It’s not a finite number but rather a variable.” Inside each disk is a mucus-like nucleus, and “if you keep flexing your spine and bending the disk over and over again when combined with compressive load, that nucleus slowly breaches the layers and causes a disk bulge, or a disk herniation,” says McGill. Again, repeated spinal flexion is one variable. Other variables include the shape of the discs (ovoid or limacon-shaped) and thickness of the spine (Yates and McGill, 2010). It is interesting to note that these two variables, shape and thickness, also influence whether or not a patient will respond to the McKenzie back rehabilitation protocol (Yates and McGill, 2010). Other variables include but are not limited to one’s occupation, hip geometry, and past medical history McGill explains in his essay entitled, “Spine flexion exercise: Myths, Truths, and Issues affecting health and performance.”
“Doing a sit-up doesn’t train your ab muscles to do the job for which they were designed –the core muscles primarily work to stop motion and allow the hip power to travel through the linkage while supporting the flexible column to prevent buckling under load,”says McGill.
Crunches and/or sit-ups place the spine in a posture similar to a sitting posture adding the cumulative effect. Look at the photos below:
Do you see a resemblance in the photos when you compare the bowed-over skeleton and the crunch/sit-up movement?
The expense of a crunch and/or sit-up is as follows:
- Traditional sit-up (knees bent with feet locked under something, sitting up from the ground to vertical) = 3300 N or 730 lbs. of compression on the spine (McGill, 88).
- Basic crunch = 2000 N of compression or 440 lbs. on the spine (McGill, 88).
- Cripton and colleagues (1995) found the shear tolerance of the spine to be in the neighborhood of 2000-2800 N in adult cadavers, for one-time loading. The mathematical breakdown: 300-500 crunches a day = 600,000 N or 133,000 lbs. of pressure on your spine and discs at a minimum.
- The National Institute of Occupational Safety and Health has set the action limit for low back compression at 3300 N. “Repetitive loading about this level is linked with higher injury rates in workers, yet this is imposed on the spine with each repetition of the sit-up!” (McGill, 88).
Do you feel that doing crunches on a stability ball may be safer or allow greater range of motion? Think again. “A curl-up with the torso over a ball and the feet on the floor virtually doubles the abdominal muscle activation and correspondingly, the spine load” (Vera-Garcia et al, 2000; McGill, 2009). Instead consider rolling over into a plank posture on the gym ball to perform the “stir the pot” exercise explained in greater detail below.
McGill suggests reducing spinal flexion movement when training the “core.” He suggests adding more spine flexion “moment” exercises. The evidence shows this increases injury resilience and performance. “This means replacing sit-ups..while challenging the core muscles with bridges, planks, stir the pot, and bird dogs to name just a few,” says McGill.
The bird dog, for instance, simply involves getting on all fours and, “while keeping the core muscles tight, extending the opposite arm and leg and then switching limbs.” I commonly place a dowel along the spine and ask clients to maintain three points of contact while performing the bird dog to ensure not only spinal stability but pelvic stability as well. In my professional opinion, the bird dog is a deceptive movement in that it appears simple while in fact, it requires intense focus to perform correctly. McGill has written a new book for the public with back pain called “Back Mechanic”. He shows progressions and “tricks” to enhance the effectiveness of these exercises such as “push the heel away” to add more gluteal and core muscle activation.
The more complex stir the pot calls for moving shoulders in a small circles clockwise and counter-clockwise while in a plank position with forearms balanced on a swiss/stability exercise ball.
McGill’s “big 3” movements are the foundation from which all other core movements are progressed from. These movements are the bird dog, the curl-up (which is not really a curl-up), and stir the pot. The “big 3” have been proven to enhance stiffness that lasts after the training session which adds more athleticism to the hips and reduces spine joint irritation (McGill, 1998 and 2014).
In the following video, McGill demonstrates proper technique:
The cause and effect relationship of low back pain and crunches/sit-ups has been addressed by some impressive groups. The US military are changing their fitness tests to get rid of sit-ups and replace them with other plank type exercises because of the evidence from many perspectives. McGill, along with several experts have been consultants. While animal studies revealed the mechanism linking repeated sit-ups with accelerated spine disorders, the military noticed elevated back disability in their soldiers but this reduced when the soldiers replaced the sit-up exercises with core stabilization exercises. Interestingly their physical performance also increased.
In 2009, a U.S. Army study replaced sit-ups with core stabilization exercises, specifically stir the pot and planks. The result? Soldiers who performed stir the pot and planks performed significantly better on their sit-up test (Childs et al, 2009).
In addition to the “Big 3,” McGill has tested and approved the plank walkout, one-arm farmer’s carry, asymmetrical carry, side plank, single-leg glute bridge, anti-extension overhead cable pulls, and many more. If you are uncertain how to perform these, just ask one of the Fitness Coaches at Pulse to assist you.
In his book, Ultimate Back Fitness and Performance, McGill states, “two movements that work the spine and back in the most biomechanically correct fashion are the deadlift and the front squat.” There are many variations such as kettle bell deadlift, off-set kettle bell deadlift, front squat, one-leg squat, single-leg deadlift, and trapbar deadlifts (McGill, 2009). “There is no isolation of the muscles, and the body works as one functional unit,” says McGill.
Some people dismiss the extensive research McGill has dedicated most of his professional career to stating he only uses “pig spines” or cadaveric tissue. In response to this debate, Professor McGill states, “These folks must live in a basement. They have seen a single study and do not know our body of work. We have published over a 100 studies with only 10% using animals.” Furthermore, he states, “We have done lots of investigation of living people with electromyography to document muscle contraction and skeletal loads—this is all done on living people so I don’t think to say we only work on cadavers is accurate.”
Other well respected researchers have demonstrated that static anti-extension exercises like the ab rollout, pike, knee tuck, and plank activate the rectus abdominus more than a crunch and also require a strong co-contraction of the abdominal muscles to prevent the spine’s hyperextension (Youdas et al, 2008).
McGill does not live in a laboratory. He is out in the field teaching experts who teach fitness professionals. Below, you can see McGill in action.
Another leading expert on this subject, Dr. Shirley Sahrmann is professor of Physical Therapy/ Neurology/ Cell Biology and Physiology at the Washington University School of Medicine in St. Louis.. In her book, Diagnosis and Treatment of Impairment Syndromes, Sahrmann states, “The primary function of the abdominal muscles is to provide isometric support…. Because the lumbar spine is not intended to rotate, a large percentage of back problems occurs because the abdominal muscles are not keeping a tight control over the rotation between the pelvis and the spine.” In other words, the abdominal muscles are there for support, not to flex. They are there to restrict rotation of the lumbar spine (lower back). The job is isometric in nature (without movement). The goal here is to teach your core to stay stable as your limbs move around it. She believes the focus on training the core should be more on anti-flexion and anti-extension.
Does a relationship exist between the glutes and the core? Professor McGill, Mike Clark, PT (National Academy of Sports Medicine), and Michael Boyle, AT, all believe so. All three experts in our field have come to the same conclusion with respect to incorporating glute activation with core work. Clark calls it “a problem of reciprocal inhibition or synergistic dominance,” while McGill uses the term “gluteal amnesia.” In fact McGill has recently proved that pain causes the brain to shut down the glutes and rather extend the hip with the hamstrings. This is a problem for several reasons in that there will be more loading on both the spine and the hip joints together with compromised performance (Freeman S, Mascia A, McGill SM 2013).
“If I can make one clear statement of what I believe now about training as it applies to the core it’s this: Glute activation, or more importantly, lack of glute activation may be the root of all our core training failures and the primary source of low back pain,” says Michael Boyle, author of Advances in Functional Training. Boyle suggests glute activation as the first thing in your warm up. “Mini-band walks or superband X-walks are great for glute medius. For glute max, use either quadruped hip extension or the Cook hip lift,” says Boyle.
Glute bridges and their progressions have proven extremely effective in waking up the glutes, especially for desk-bound office workers. I have developed a bridge progression series and would love to share this with anyone who is interested.
Bottom line: Everyone needs a strong core, but the crunch is a one- plane dominant (uni-planar) exercise that primarily works the rectus abdominus. Conventional wisdom may not always be correct. We should stay abreast with evolving scientific literature and move forward. There is a preponderance of research demonstrating better and safer ways to make our core muscles not only stronger but more functional.
Where can you find more information on Stu McGill? Many of Stu’s original scientific papers can be found on his CV on the University’s website:
Most of his research studies have be compiled and organized in his book: Ultimate Back Fitness and Performance, 5th edition (available from www.backfitpro.com).
In addition, Stu McGills new book written for the public with back pain entitled,
Back Mechanic: The step by step McGill method to fix back pain (available from www.backfitpro.com). In a nutshell, it guides the reader through a self assessment of their back pain triggers. Once these are revealed he shows you what to stop doing and what to do instead.
Our coaches are experts on form, technique and the right exercises for you! Contact us today to learn more.
Callaghan JP, McGill SM, Intervertebral disc herniation: studies on a porcine model exposed to highly repetitive flexion/extension motion with compressive force. Clin Biomech (Bristol, Avon). 2001 Jan;16(1):28-37.
Childs, J.D., George, S.Z., Wright, A., Dugan, J.L., Benedict, T., Bush, J., Fortenberry, A., Preston, J., McQueen, R., Teyhen, D.S., (2009) The effects of traditional sit-up training versus core stabilization exercises on sit-up performance in US Army Soldiers: A cluster randomized trial, J. Orthop. Sports Phys. Ther., 39(1): A18.
Contreras, B., & Schoenfeld, B. (2011). To Crunch or Not to Crunch: An Evidence-Based Examination of Spinal Flexion Exercises, Their Potential Risks, and Their Applicability to Program Design. Strength and Conditioning Journal, 33(4), 8-18.
Freeman S, Mascia A, McGill SM (2013). Arthrogenic neuromuscular inhibition: A foundational investigation of existence in the hip joint. Clin Biomech. 28:171-177.
He’s Got Our Backs.” Kinesiology. 2012. Web. 13, 2012. <https://uwaterloo.ca/kinesiology/hes-got-our-backs.
McGill, S. (2009). Ultimate back fitness and performance. Waterloo, Ont.: Backfitpro
McGill, Stu “Spinal Flexion Myths, Truths, and Issues” Essay, University of Waterloo and BackFit Pro Inc.
Shirley Sahmann, Diagnosis and Treatement of Movemetn Impairment Syndromes, p. 70 Mosby 2002.
Tampier, C., Drake, J., Callaghan, J., McGill, S.M. (2007) Progressive disc herniation: An investigation of the mechanism using radiologic, histochemical and microscopic dissection techniques. SPINE, 32(25): 2869-2874.
Vera-Garcia, F.J., Grenier, S.G., and McGill, S.M. (2000) Abdominal response during curl-ups on both stable and labile surfaces. Phys. Ther. 80(6): 564-569.
Veres, S.P., Robertson, P.A., Broom, N.D., (2009) The morphology of acute disc herniation: A clinically relevant model defining the role of flexion. SPINE: 34(21):2288-2296.
Youdas JW, Guck BR, Hebrink RC, Rugotzke JD, Madson TJ, Hollman JH, An electromyographic analysis of the Ab-Slide exercise, abdominal crunch, supine double leg thrust, and side bridge in healthy young adults: implications for rehabilitation professionals, J Strength Cond Res, Nov;22(6):1939-46, 2008.