Crunches or no crunches? Part 1

One of the most heated discussions in the field of weight training revolves around whether or not to perform crunches. It's amazing to see that this seemingly innocuous, short-range-of-motion exercise has caused such a rift between so many strength and conditioning professionals - and the debate continues.

At the center of this debate are studies using pig cadavers that show that repetitive flexion of the spine can lead to disc herniation. These in vitro studies seem to indicate that lumbar flexion is a potent disc herniation-inducing mechanism, and opponents of the use of crunches have extrapolated from these studies that the human spine can withstand a limited number of flexion cycles over its lifespan without damage.

Accordingly, these people recommend that exercises such as crunches that involve flexion of the spine should be avoided at all costs. However, while this may seem logical at first glance, this issue is more complex than it may initially appear.

Someone needs to stand up and do something about that 2000 pound gorilla soiling the carpet. We know dozens of respected strength coaches, physical therapists, personal trainers and medical professionals who have serious doubts about the dangers of crunches, but no one dares to seriously discuss this topic for fear of jeopardizing their reputation.

This must come to an end!

Fitness is a religion

Humans have a natural need to follow a school of thought, follow a leader, believe in supernatural phenomena and rebel against scientific principles. Throughout human history, scientists have been punished for questioning the current dogma. Sadly, this is no different in the fitness industry.

Many fitness professionals have looked for a culprit for lower back pain and jumped on the anti-crunches bandwagon without critical inquiry. These people have adopted absurdly rigid views regarding the lumbar spine, believing that you should move this area of the body as little as possible to protect the spine - going so far as to alter the normal biomechanics of daily life.

In the next step, they have put pressure on others to jump on this bandwagon as well and they become very emotional when confronted with this issue. This is the antithesis of scientific thinking. We are lucky that we are not under house arrest like Galileo for his hypothesis that the earth is not the center of the universe.

After taking a closer look at the subject, reviewing the scientific literature and applying our critical thinking skills, we have come to the conclusion that a reasonable dose of exercises that bend the spine is good for you and that it is not necessary to avoid these exercises.

We presented our position in a review paper published in the Strength & Conditioning Journal, and while we won't repeat everything from that review in this article, we continue to question the current "anti-crunches" movement and propose a plausible alternative theory.

In our journal article, we addressed the following topics, which we will only summarize briefly and concisely below. For more detailed explanations and study citations, we encourage the interested reader to read our journal article in full.

Methodological issues in studies against exercises involving lumbar flexion

• Removal of the muscles: The experiments used in the study to refute the use of lumbar flexion exercises used the spines of pigs from which the muscles had been removed, altering the biomechanics of the spine.
• No fluid in the cadavers: Spines in cadavers do not function in the same way as living spines because the fluid does not flow back into the intervertebral discs as it does in living tissue.
• The range of motion of the porcine spine: the porcine spine has a smaller flexion and extension range of motion than the lumbar spine in humans.
• The movement of crunches has not been mimicked correctly: when most people perform crunches, they perform a few sets of 10 or 20 repetitions and then wait a few days before performing the exercise again. This allows the discs to regenerate and remodel. However, the studies used to refute crunches involved thousands of cycles of lumbar spine flexion without rest, which in no way mimics athletic training. It should also be noted that cadaveric spines do not remodel, whereas living spines do.
• Genetics: In the world of disc degeneration, the role of genetics is enormous. It seems that some individuals are highly susceptible to disc problems, while others are not. This suggests that optimal design of an exercise program would require knowledge of genetic predispositions.
• Range of motion of the crunch exercise: many years ago, an NSCA Journal article described the proper execution of crunches, which involves a 30 degree flexion of the trunk, with the majority of the movement occurring in the thoracic spine rather than the lumbar spine. If the lumbar spine does not approach the point of maximal flexion when performing crunches, then these studies are not applicable to this exercise.
• Intra-abdominal pressure controversy: There is a possibility that models used to estimate compressive forces during the performance of crunches have been overestimated because the role of intra-abdominal pressure (pressure within the abdomen) has not been taken into account. If this is the case, then the studies may have used too much pressure in combination with the aforementioned excessive range of motion, which would make these studies inapplicable to crunches. However, there are a number of conflicting studies in this area and it is likely that this effect is not significant.

Potential benefits of lumbar flexion exercises

• Increased blood flow and nutrient delivery to the intervertebral discs: Flexion of the lumbar spine increases the delivery of nutrients to the intervertebral discs by increasing the supply of nutrient-transporting fluids to the discs.
• Increased tissue remodeling: the correct dosage of spinal flexion is likely to strengthen the tissues of the intervertebral discs, which would therefore increase resistance to lumbar flexion exercises and prevent future injuries.
• Sagittal plane mobility: some studies have linked a lack of spinal mobility to lower back pain, although the literature on this topic is somewhat contradictory. What is clear, however, is that crunches can prevent loss of spinal mobility, which may be important in preventing lower back pain.
• Rectus abdominis hypertrophy: when you consider the overall knowledge of hypertrophy, it quickly becomes clear that dynamic training is superior to isometric training when it comes to building muscle mass. Much of this has to do with the increased muscle damage caused by eccentric activity, as well as the increased metabolic stress. So if you want to improve the appearance of your six-pack, then flexion exercises will certainly help you achieve this goal.
• Performance enhancement: Contrary to what some have claimed, lumbar flexion is common in many athletic activities. Therefore, concentric/eccentric strengthening of the abdominal muscles may very well lead to increased athletic performance.

Anecdotes and other arguments

Let's now look at some anecdotal evidence to support our claims.

If there really is a finite number of flexion cycles, where does that number lie?

Several fitness experts have suggested that the human lumbar spine has a limited number of flexion cycles and they believe that we should save these cycles for activities of daily living such as tying shoes rather than wasting them on crunches. Even if you keep in mind that anecdotal evidence proves nothing, it is still interesting to look for such evidence and see if it can provide a basis for a theoretical justification.

• In 2003, the Brazilian fitness trainer Edmar Freitas performed 133,986 crunches within 30 hours, setting a world record. With this achievement, he surpassed his record from the previous year, which had been 111,000 sit-ups within 24 hours.
• Manny Pacquiao, one of the best boxers in the world, performs 4,000 sit-ups per day.
• And last but not least, there's Herschel Walker, American football legend, Olympic bobsledder and new MMA hopeful, who has been doing 3,500 sit-ups a day since his high school days. He started practicing sit-ups when he was 12 years old. Considering he's 49 years old today, that's the equivalent of 47,267,500 situps. That's almost 50 million flexion cycles under compression load!

Of course, you could argue that all of these individuals may have ruined their spine by doing this and that if you were to get MRI images of these people, you would probably see scary degeneration of the discs, but we doubt that this would be the case. Instead, we believe this is clear evidence that the discs can remodel and become stronger over time to resist the damage that spinal flexion exercise can cause.

Another argument that could be made is that these people are outliers and their exceptional genetics allow for such amazing flexion cycles. However, we disagree with this and believe that there are probably many individuals who unknowingly achieve similar numbers over the course of their lives. Rather, we believe that this is evidence that muscular balance, abdominal muscle strength and flexion exercises can protect the spine.

Should we shoot ourselves now?

If we were to target specific disc studies to determine what forms of exercise we should be doing, then we shouldn't really be doing anything at all.

We found 13 studies that suggest spinal flexion is a bad idea (Callaghan and McGill, 2001; Drake et al, 2005; Tampier et al, 2007; Drake and Callaghan, 2009; Marshall and McGill, 2010; Adams and Hutton, 1982; Adams and Hutton, 1983; Adams and Hutton, 1985; Lindblom 1957; Brown et al, 1957; Hardy, 1958; Veres et al, 2009; Court et al, 2001). This means neither crunches nor sit-ups.

We found 11 studies showing that combinations of spinal loading are not a good idea. (Gordon et al. 1991 (flexion and rotation); McNally et al. 1993 (flexion and external flexion); Shirazi 1989 (lateral flexion and rotation); Kelsey et al. 1984 (flexion and rotation); Adams et al. 2000 (complex); Marshall and McGill, 2010 (flexion/extension and rotation); Drake et al. 2005 (flexion and rotation); Veres et al, 2010 (flexion and rotation); Schmidt et al. 2007 (lateral bending and rotation, lateral bending and flexion, lateral bending and extension); Schmidt et al. 2007 (lateral bending and flexion, lateral bending and rotation, flexion and rotation); Schmidt et al. 2009 (lateral bending and flexion, lateral bending and extension). This does not include exercises such as sit-ups with rotation of the upper body or Russian twists(https://www.youtube.com/watch?v=NeAtimSCxsY).

We also found a few studies showing that spinal extension is a big no-no (Adams et al., 2000; Shah et al., 1978). This means no supermans(https://www.youtube.com/watch?v=z6PJMT2y8GQ).

Several studies show that spinal rotation is bad (Krismer et al, 1996; Aultman et al, 2004; Farfan et al, 1970). This means no wood chopping exercises on the cable pulley (https://www.youtube.com/watch?v=DoACGlPyQTI). And you'd better not do these exercises on a vibrating platform either, as this would be a double whammy for your spine. Other studies have shown that vibrations are bad for the intervertebral discs (Dupuis and Zerlett 1987).

There is research to suggest that side bending is bad for you (Costi et al. 2007; Natarajan et al. 2008). This does not mean side bending. Similarly, asymmetrical exercises have also been shown to lead to negative results (Natarajan et al. 2008). This does not mean unilateral exercises or loaded carries.

And here's where things start to get interesting. We found 18 different studies showing that static or dynamic compression is a very bad idea (Virgin 1951; Liu et al. 1983; Lai et al. 2008; Lotz et al. 1998; Tsai et al. 1998; Iatridis et al. 1999; Lotz et al. 1998; Kroeber et al. 2002; MacLean et al. 2003; Hsieh and Lotz 2003; MacLean et al. 2004; Ching et al. 2004; Masouka et al. 2007; Veres et al. 2008; Lai and Chow 2010; Nakamura et al. 2009; Wang et al. 2007; Huang and Gu 2008).

This means not only no squats, deadlifts and core stability exercises, but also no physical activities that involve free weights of any kind, as muscle contractions generate a compression load on the spine. We should have known this because training with heavy weights is bad for the back (Lee and Chiou 1994; Kelsey et al. 1984), as is overactivity (Videman and Battie, 1999). So now we know that training with weights and intense training are out.

And it goes on and on. We've found studies that suggest that all kinds of activities of daily living are bad for the back - even sitting and bed rest. Perhaps we should shoot ourselves now before we become completely immobile.

In the second part of this article, we will address the question of whether crunches can have negative effects on posture and get to the bottom of whether crunches are a functional exercise. Finally, we will get to the bottom of the question of whether there is such a thing as healing and regeneration of the intervertebral discs.

Source: https://www.t-nation.com/training/to-crunch-or-not-to-crunch

By Bret Contreras, Brad Schoenfeld, PhD