Crunches or no crunches? Part 2

After taking a critical look at the arguments put forward by opponents of crunches in the first part regarding damage to the spine caused by performing this exercise, in this second part of the article we will address the question of whether crunches can have negative effects on posture and get to the bottom of the question 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.

Do crunches ruin your posture?

The theory goes along the following lines: crunches shorten the rectus abdominis. As the rectus abdominis runs from the sternum/chest to the pelvis, continuously shortening this muscle will pull your chest downwards, which will ultimately result in a curvature of the spine (i.e. a rounded back posture). This is an interesting theory, but it also lacks any basis in fact.

As with many theories, the essence of this claim is based on a grain of truth. If you put a muscle in a shortened position for a prolonged period of time, this will result in that muscle having a shorter length at rest. For example, if you immobilize your arm in a flexed position for several weeks, your arm will tend to stay in that flexed position when you remove the splint.

This is the result of an adaptive response in which the elbow flexors (i.e. biceps, brachialis, etc.) lose sarcomeres while sarcomeres are added to the antagonistic extensor muscle (Toigo & Boutellier, 2006). This is also known as adaptive shortening.

You may already recognize the flaw in the hypothesis that performing crunches will shorten your rectus abdominis - crunches are not just a shortening exercise! In addition to this, crunches also include eccentric actions, during which the rectus abdominis returns to its resting length. Thus, any negative effects of shortening contractions on the number of sarcomeres would be offset by the lengthening actions of the eccentric actions. The net effect would be no change in length at rest.

Some anti-crunches supporters also argue that performing spinal flexion exercises (e.g. crunches) will over-strengthen the rectus abdominis so that it becomes overly strong compared to its antagonists and will therefore pull the chest down.

This is a straw man argument. Of course it's true that an imbalance between different muscles can cause poor posture - I'm sure the reader is familiar with exercisers who train chest and arms during every session and achieve such a leaned forward posture that they will have trouble scratching the back of their head. But that doesn't mean you shouldn't do bench presses and curls.

The problem here is rather a poor design of the training program and not a specific exercise.

As for crunches, the same principle applies. Of course, if you do a million crunches a day and don't train other muscle groups, you will increase the risk of postural damage.

However, this is not a problem if you use a balanced exercise program. Performing virtually any exercise while standing and not on machines will heavily engage the core muscles, especially the back muscles, which are antagonists of the rectus abdominis (Schoenfeld, 2010, Lehman, 2005). It should also be noted that the average person tends to have weak abdominal muscles (Morris et al. 2006), which means that most of us could benefit from performing spinal flexion exercises.

In summary, there is no convincing evidence that performing crunches as part of a full-body resistance training program will have any negative effects on posture.

Do crunches lead to additional dysfunctions such as respiratory dysfunction or gluteus dysfunction?

If crunches really did pull the chest down and cause kyphosis (curvature of the spine), then it could be speculated that this could affect breathing and gluteus function. However, as mentioned above, this is very unlikely to be the case.

Anecdotally, hundreds of thousands of athletes have achieved amazing results over the last few decades despite performing crunches. If crunches really did shorten the abdominal muscles, then considering that the majority of people - athletes included - have a forward tilt of the pelvis, one could argue that it would be wise to perform crunches to pull the pelvis upwards, which would theoretically reduce a forward tilt of the pelvis and lead to a more neutral lumbar-pelvic posture.

Are crunches a non-functional exercise?

Whenever someone questions the implication that crunches are about as dangerous as wakeboarding in a tsunami, the anti-crunches movement is quick to say something like, "Who cares if crunches are dangerous or not? Crunches are not functional. They are a short range of motion exercise that you do lying on your back on the floor. This exercise cannot possibly have a carryover to anything."

Our mentor Mel Siff has aptly commented on this:

"Functional training is any form of training that improves any relevant biomotor skill and is not accompanied by impairment of other biomotor skills."

Opponents of crunches will point out that crunches only involve your own body weight and are therefore not "heavy" enough to have carryover to movements performed at high force or high speed. This statement is absurd as it is very easy to hold a dumbbell in front of your chest to increase the intensity of the exercise. You can also perform kneeling crunches on the cable pulley to increase the intensity of the exercise.

What has the best carryover to a functional activity depends on the task. Here is a table that should help you determine the optimal carryover of the workout.

Biomotor ability	Examples	Exercise category	Examples
Rotation of the trunk: stability, strength and power	Throwing a football or baseball, throwing a discus, swinging a bat, hitting a left hook	Rotation exercises and anti-rotation exercises	Woodchops, landmines, pallof presses, cable chops
Lateral flexion of the trunk: stability, strength and power	Taking a punch	Lateral flexion exercises and antilateral flexion exercises	Side bends, side planks, suitcase carries
Flexion of the trunk: stability, strength and power	Standing up from a bench, gymnastics exercises on a bar, performing a punch to the center of the body, resisting a push backwards as in sumo wrestling, throwing a soccer overhead	Flexion exercises and anti-extension exercises	Crunches, sit-ups, hanging leg raises, planks, ab wheel rollouts, bodysaws
Extension of the trunk: stability, strength and power	Carrying heavy loads, picking up objects from the floor, remaining upright during close combat.	Extension exercises and anti-flexion exercises	Squats, deadlifts, back extensions, reverse hypers, farmers walk, zercher carries

Basically, stability exercises seem to be better for stabilization tasks and tasks that require proper core function, while strengthening exercises seem to be better for dynamic tasks and hypertrophy.

As you can see, an exercise like crunches with added weight can have carryover to a variety of tasks and therefore should not be maligned for its applicability to functional or athletic performance.

Is there a healthy balance and can intervertebral discs remodel and heal?

Many doctors say that intervertebral discs cannot heal. However, this statement is misleading, it is true that discs are poorly perfused and struggle to receive adequate amounts of nutrients and it is also true that disc tissue does not heal quickly. Proteoglycan turnover can take 500 days (Urban et al. 1978) and collagen turnover can take even longer (Adams and Hutton 1982).

For this reason, the rate of remodeling of intervertebral discs lags behind that of other skeletal tissue structures (Maroudas et al. 1975; Skrzypiec et al. 2007).

However, there is ample evidence of disc healing. Common sense would dictate that intervertebral discs heal, otherwise there would never be an improvement after an injury in the area of the intervertebral discs. In this case, the condition of our intervertebral discs would have to get worse and worse until we could no longer move at all.

Based on epidemiological studies, it is clear that there is an optimal window for spinal loading that lies somewhere between bed rest and overactivity (Videman et al., 1990).

It has been shown that there is a healthy balance between spinal compression (Hutton et al. 1998; Lotz et al. 2002; Walsh and Lotz 2004; Wuertz et al. 2009; MacLean et al. 2005) and spinal rotation (Chan et al. 2011). It has also been shown that there are positive aspects of spinal flexion on the intervertebral discs (Lotz et al. 2008; Court et al. 2001).

In addition, 16 different studies suggest that the intervertebral discs can remodel and heal themselves. While several papers have looked at this issue (Lotz 2004; Stokes and Latridis; Adams and Dolan 1997; Porter 1987), others have shown that flexion damage can heal (Court et al. 2007), that compression damage can heal (Lai et al. 2008; Korecki et al. 2008; MacLean et al. 2008; Hee et al. 2011), that prolapse can regress (Scannell and McGill 2009), that herniations can improve (Girard et al. 2004; Wood et al. 1997), that the outer annulus of the discs can become stronger (Skrzpiec et al. 2007), that the collagen within the discs can be remodeled to become stronger (Brickley-Parsons and Glimcher, 1984), and that the spine and ligaments can become stronger to better withstand loading (Porter et al. 1989; Adams and Dolan 1996).

Every time you move your spine, you cause microtrauma, which triggers anabolic and catabolic processes. Ideally, the extent of damage should be minimized, as the healing of major damage weakens the intervertebral discs biomechanically.

Damage to the rim of the discs, for example, is repaired by granulation tissue and the scar tissue never regains its normal lamellar architecture (Hampton et al. 1989). Endplate injuries heal with cartilaginous tissue (Cinotti et al. 2005; Holm et al. 2004), fibrocartilage replaces nuclear material (Kim et al. 2005), and healing of damaged tissue often results in replacement of the tissue with a thin layer of weaker fibrous tissue (Fazzalari et al. 2001).

A stress-eustress solution?

The stress-eustress theory of training

The study of biomechanics is unique in that one must consider not only forces and stresses acting on human tissue, but also adaptive remodeling. An ideal training program does not avoid stress, but keeps the body in a state of eustress while avoiding overload, which ensures that anabolic agents within the tissues do more work than catabolic agents within the tissues to promote complete repair, regeneration and strengthening.

Conclusion

We hope we have given the reader some food for thought and encouraged them to rely on logic rather than emotion when making decisions about exercise safety and program design. An intelligent exerciser will weigh the available facts and make appropriate, dispassionate decisions without rigidly clinging to prevailing opinions.

We believe that future research will help to confirm the safety and harmlessness of crunches. However, this will require human studies that include MRI scans and appropriate training interventions to ensure the use of correct technique when performing crunches.

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

By Bret Contreras, Brad Schoenfeld, PhD