Dr Wendi's Health

What’s the deal with crunches? Are they good or bad for you?

What’s the deal with crunches? Are they good or bad for you?

I have seen several articles online that say things like “doing crunches is bad for your back”, “exercises to NEVER do…crunches”, “doing crunches is a waste of time”.  So I decided to see what research has to say on the topic.

Some research seems to indicate that flexion movements like crunches are a contributing factor to degenerating discs and some people in the fitness industry believe that we have a set number of flexion motions our spine can handle and then we will have spine problems so we shouldn’t ‘waste’ precious flexion movements on crunches.

A quick look at disc degeneration.  Disc degeneration occurs gradually as we age but some factors can increase this rate, mainly:

  • Decreased production of proteoglycans (carbohydrates in the cushion part that attracts water and helps discs absorb shock and deal with pressure), and collagen (a connective tissue protein that makes tissues strong) as we age

  • Mechanical loading – so carrying/lifting heavy weight would have an impact on spinal discs over time

  • Wear and tear over time increases the production of fibrous material – tough tissue that is your body’s attempt to stabilize the area to prevent damage but can lead to decreased mobility and pain

So why would flexion, bending forward, cause disc problems? 

Some studies were done in vitro (meaning in a glass, basically they used cadaver parts) or in animal models.  The attempt was to simulate comparable strain that would be caused by doing crunches and these studies showed that disc damage did occur.  The issue is though that these in vitro studies used vertebrae and discs from cadavers where the musculature was removed.  In a normal spine we have muscles that support and stabilize the spine.  Also, cadaver tissue also does not have the ability to repair after use, so over time the damage is quite progressive.  The studies done using animals (mostly pigs) are also not indicative of what happens in humans because they walk on 4 legs and have less range of motion compared to humans.  The full review article is referenced below if you want to read more details about the studies.

So what are the conclusions?  Crunches are NOT bad for your spine and they are NOT going to increase the rate of spinal degeneration.  So if you were hoping for a valid reason for never doing another crunch again then well, sorry to let you down. 

Here are a list of benefits for spinal flexion exercises like crunches:

  • facilitates nutrient delivery to intervertebral discs – the lack of nutrients moving into the discs is thought to be a major cause of disc degeneration
  • flexion movements increase nutrient diffusion to posterior portion of the discs whereas postural muscle contractions primarily favour anterior diffusion
  • increases tensile stress on the posterior portion of the discs that has a protective effect against inflammation 
  • improves functional range of motion
  • increases abdominal muscle strength
  • increases spinal ligament and tendon strength
  • resistance training for abdominal and spinal muscles is a key way to prevent lower back injuries

Another argument I hear about why we should not do crunches, or why crunches are a waste of time is that they don’t give you 6-pack abs.

These statements are kind of true and not true at the same time, let me explain.

  1. Crunches DO make your abs stronger and help you to build muscle.  You will not have a 6-pack if you don’t stimulate ab muscle growth – doesn’t have to be crunches, there are many ways to work your abs but in the end, you have to put in the work
  2. Crunches DON’T burn fat that is specifically on your abs. If you want to see your abs then you have to burn the fat that is covering them up.  You can only do this by losing overall body fat and that means you have to eat less total calories than you burn or burn more than you eat. 

References

5 comments

you don’t have to go up as much as I have in this pic, you just have to move off the floor enough to feel your abs contracting 🙂

Finally some real facts on crunches! Do you think they are better with feet on the floor, or raised like a sitting position?

I don’t think it should matter because a crunch isn’t a full sit-up; you only need to move a few inches to make the abs contract. Also, the thoracic (chest) region is technically flexing the most as opposed to your lumbar (lower) back region, it should not bother your lower back either way. But go with whichever feels the most comfortable, and as long as the abs are contracting then they are getting a good workout 🙂

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