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Crunches Don't Make Flat Stomachs, Hurt Backs...Maybe

Posted Dec 23 2012 12:41am
If I was to guess, the abdominal crunch (partial sit-up) is the most popular exercise in the gym.  I think most people are under the impression doing crunches will melt the fat away from their midsection.  This is as wrong as a nun wearing garters.  It just doesn't work that way.  Exercising a certain body part does not cause a direct decrease of body-fat in that area.  You can not spot reduce adipose tissue.  Unlike muscle cells, fat cells do not change after repeated bouts of mechanical stress.  Many factors will combine to decrease or increase the adiposity in your abdominal region.  Performing ab exercises will not directly affect the fat in your love handles, pouch and/or beer belly and may in fact cause you harm.

Crunches may actually increase the muscle bulk around your midsection and add to your girth.  This is especially true for the neophyte gym-goers.  When you first start doing crunches the abdominal muscles will increase in size, pushing the fat farther out giving you the appearance of a larger waist.  But as your body adapts and you begin to lose weight (due to diet, increased metabolism, cardio and weight training) you might start to see the beginnings of 'boxes' and your stomach muscles will reach a threshold.  The majority of crunchers don't do 1 rep maximal sets (come to think about it, I've never seen it done) or progressively increase the load - plus the rectus abdominus has a limited capacity for hypertrophy. So don't get your knickers in a twist, crunches won't make you fat.  

Like drugs, all exercises are dangerous and have the potential to cause great harm or good.   Depending on your goals and limitations you should weigh the pros and cons of all the exercises you select. 

Crunches Pros
  • Strengthens lumbar flexion
  • Strengthens rectus abdominus 
  • Increases nutrient flow to lumbar discs
  • Increases forward spinal flexion mobility
  • Potentially a performance enhancing movement 
Crunches Cons
  • Puts a lot of stress on the lumbar spine (about 674 lbs. of force)
  • Uses a limited amount of muscles within the core 
  • If you sit for more than 6 hours a day your lumbar spine is flexed (stretched) and your abdominals are shortened for that whole time which leads to a structural imbalance that crunches will make worse- eventually leading to a injury.  
  • Most people don't bother to work the antagonist (opposing) muscles i.e. erector spinae and create an even larger imbalance which open you up for injury   
  • Crunches are stable and train a limited range with very little co-contraction from the stabilizing and secondary muscles.  A crunch is functional for getting up from the couch and bed but that's about it.
There are many professional athletes and gym-goers who have been doing 10's of thousands of crunches in their lifetime and never been hurt.   So should you stop doing crunches?  That depends.  If you have or are prone to lower back pain/injuries I would recommend doing a limited amount of spinal flexion (crunch) if any.  If strong trunk flexion is part of your fitness goals because it will help you with martial arts, boxing, throwing, gymnastics etc. then I would certainly keep crunches in your program. 

The "core" musculature is in charge of stabilizing the spine, decelerating the body, preventing and creating middle and lower back rotation, flexion and extension.  It takes many muscles to perform these feats and they need to work in specific patterns to pull it off.  If your core training is limited to crunches you are likely building an asymmetrical house of cards.  It is important to have a well rounded core training program that properly engages movement patterns and builds better performance. 

If you desire a flat stomach there are some better exercises to achieve this goal.  Namely the plank and all of its variations (some listed below).  This is such a great exercise because it engages your inner core musculature including your transverse abdominals (TVA).  These muscles do more to flatten you stomach then any crunch will ever do.  Your TVA (the stomach's corset) is in charge of holding in your internal organs, protecting your spine, and stabilizing your trunk during all movement.   If you'd like to feel it work, put your hand on your stomach and cough.  The tightness you felt is the TVA contracting .   It is a common mistake to neglect the inner core muscles and work solely on the obliques and rectus abs.  I've seen many people with six packs that still have weak inner cores.  I call it a "fat six-pack".   This is due to one or two things: enervation of the inner core musculature specifically the TVA and/or hypertrophy of the internal organs due to steroids and human growth hormone.

If a flat stomach is your goal, the exercises listed below will engage your inner core (TVA,  erector spinae, multifidus, longissimus, diaphragm and pelvic muscles)  and help build a strong and stable unit.  

Elbow Plank
Side Plank
Oscillating Plank on a Ball
Moving Plank Contralateral lifts
Low/High Wood Chops
Front Squats
Supine Bridges
Vacuum  Exercise (isometric)
Dead Lifts
Bird Dogs 

This is just a sprinkling of core exercises that don't involve a crunch, there are many more.   Play around with your exercise program, hire a trainer and find what works best for you.  The thing is, if we didn't spend most of our days sitting we'd wouldn't have to work so hard for a flat stomach to begin with.  I guess this is another one of our first world problems. 

2. S. Mcgill; Low Back Disorders: Evidence Based Prevention and Rehabilitation, Human Kinetics, 2002.
3. C, Richardson; C, Hodges; Therapeutic Exercise For Lumbopelvic Stabilization: A Motor Control Approach For The Treatment And Prevention Of Low Back Pain,
4. M. Siff; Supertraining; 1995.
Doug Joachim - NYC
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