That was difficult to type, because in my mind, there is no such thing as a ‘bad’ or a ‘good’ exercise – it all depends on context.  Therefore I am hesitant to write that somewhat sensationalist title.

With that said, I am a big advocate of knowing your goal, and training with that goal in mind.  So let’s take a closer look at these two exercises, and discuss them in the context of a variety of health and fitness-related goals, to determine their true value in a fitness program.

What are these exercises?

First, let’s accurately describe the exercises in question.  They are both low weight (limited by body weight in both cases, but in different ways) exercises performed through a small, or no, range of motion at the lumbar spine.

In any exercise, specificity is king.  What does this mean?  The adaptations of the body are specific to the demands imposed upon it.  With this in mind, an exercise is only as good or bad as the context in which it is used.  Squats are a great exercise to increase squat strength, but not as great at increasing your ability to jog 5 miles.  Squats are less specific to that goal.  That’s not to say that squats have no place in a runner’s training – just the opposite.  Squats will increase the strength of the muscles of the legs, and assist in weight loss, both of which will be advantageous for running performance.  However, the degree to which an exercise is beneficial is dependent on:

1. How it stresses the body, and
2. Is it stressing the body in a similar way to the outcome that we desire?

Which is why I want to address the reasons why planks and crunches are a waste of time for almost everyone, depending on a variety of fitness goals.  So…

What is your fitness goal?  

Aesthetics? Yes, everyone wants the shredded six pack look, and there is nothing wrong with that. Unfortunately, planks and crunches alone won’t get you there (Vispute et al. 2011).  The visibility of abdominals is associated with body fat percentage, and the size of the underlying muscle.   In fact, the estimated body fat percentage associated with visible abdominals may be below that which is considered healthy for normal organ function and reproductive health, especially for females (Gallagher et al. 2000).  If looking good were as easy as doing some crunches and planks, everyone on the planet would have a six pack, and they wouldn’t be quite as desirable, now would they?

Muscle size?  There is evidence that high volume, low weight exercises can be effective in increasing the size of a muscle (Mitchell et al. 2012) – provided that the exercise is performed until muscle failure.  In other words, the point at which a muscle is fatigued such that it can no longer produce sufficient force – NOT, the point of ‘I’m kinda tired, I think I will stop here.’  Also, the growth potential for the abdominals may be limited by their anatomy; they are enclosed in a tendinous sheath, and as such, might not ‘explode’ like other muscles (think of a bodybuilder’s quads, calves, biceps, etc.).  Finally, keep in mind that increasing the size of the abdominals will not do much to help reach your aesthetic goals if they are covered in a layer of fat.

Core strength? The core consists of many muscles in addition to the abdominals.  Not to mention that there is no true definition of the mystical ‘core’ (Hofmann 2013a).

Ok, fine… abdominal strength?  Increasing the strength of the abdominals – OR ANY MUSCLE – means progressive overload.  In other words, increasing the amount of force that these muscles have to contract against.  Any strength exercise that you can perform fifty repetitions of is not using sufficient weight to properly stimulate strength increases in the targeted muscles.  If we extend this idea to the progressive overload principle, then crunches and planks won’t really help in this quest.  Find an exercise that is challenging to these muscles that you can only do a couple of times before muscle failure IF strength is the goal.  This holds true for any muscle or group of muscles, not just the abdominals!

Core stability? What does this even mean?  It is a big buzz term in the fitness industry that has no real meaning, consistent definition (Hofmann 2013b), or correlation to performance (Hofmann 2013c).  Regardless, if you are interested in increasing your ability to stabilize the lumbar spine against externally applied forces, increasing the strength of all muscles of the trunk and abdomen will assist in this goal.  See ‘abdominal strength’ above.

Balance? Balance does not come from your core, it primarily comes from the ankle.  If you don’t believe me, stand upright on one leg and watch your ankle.  In fact, using your core to adjust your balance is a mistake, considering about 60% of your body weight is in the HAT (Head, Arms, and Trunk).  The closest interface between your body and your base of support is your foot/ankle, and it is doing all the micro-adjusting to ensure your center of gravity remains over your base of support.

Isolation? Maybe you perform these exercises because you’d like an effective way to isolate the abdominals during training.  For a minute, we will ignore the fact that trunk and upper body consist of many more muscles than just the abdominals (although so many people associate the ‘core’ with just the abs!).  There are many situations in which one will want to isolate a muscle, but these two exercises are not going to get it done, as they can also result in a lot of hip flexor or lumbar spine extensor recruitment depending on your posture or technique (Escamilla et al. 2006, Snarr and Esco 2014).

Running performance? Many runners advocate that these exercises are critical for increasing running performance.  But many studies (Hofmann 2013c, [Link to Truth on Fitness Part 3]) have demonstrated that core-focused performance tests (consisting of, you guessed it, planks and crunches) do not correlate very well to athletic performance.  “But runners have abs!”  They also have very low body fat percentage, because they are burning quite a bit of calories, especially when training at very high levels.  Just because you can see one’s abdominals does not mean that they are particularly strong… and in this case, it doesn’t seem to matter anyway.

Endurance? Now we are getting warmer.  Planks and crunches are two different types of endurance exercise.  The principle of progressive overload applies to not just strength, but time, volume, and/or frequency of the stresses you impose on the muscle.  Both of these exercises to some extent will increase the endurance of the abdominal muscles, provided the demands of the exercise (more repetitions or longer duration) are steadily increased over time.  I would, however, caution anyone who believes that muscular endurance of the abdominals carries over to cardiovascular endurance (they are different)!

Weight loss?  Well, yes, technically both of these exercises will contribute to weight loss.  Eating a candy bar can also help contribute to weight loss, provided it is done in moderation and part of a well-balanced diet.  In fact, any movement will help contribute to weight loss… but not as much as fixing your diet will!

Enjoyment? If you or a client finds these exercises fun, challenging, and interesting, by all means!  Not all exercises need to be for physical health; our mental health is important, too.  If the goal of the exercise is to have fun, then go for it.  However, nothing is more fun than getting results!

Increase my plank time? Bingo!  Planks are great for increasing your ability to plank.  If that is your goal, then who is anyone else to judge?  Go for it!  You may also be thinking that there are certain fitness tests that involve performing a maximum number of crunches in a minute.  In that case, of course performing crunches will assist in your goal of performing crunches!

With all of that said…

The muscles of the trunk (the ‘core’) should be trained just like any other muscle in the body.  In fact, there is nothing special or different about them.  So jump on a strength machine that isolates these muscles, or perform some of the traditional major barbell lifts (bench, squat, deadlift) – all of which are demanding to the core musculature.  After a strength session targeting these muscles, give them adequate rest (24-72 hours), then train them again.  Don’t have access to equipment/barbells/etc. like this?  That’s fine, but just keep in mind that exercises like planks and crunches will be limited in their ability to ultimately help you reach your fitness goals.

There is nothing wrong with being primarily concerned with losing weight and looking better, we are human after all.  However, I believe that the allure of having a six pack is clouding the judgment of many with respect to the importance of, and training of, the infamous core.

References

1. Hofmann (2013a) Are we mystified by the core? Part I [http://media.cybexintl.com/cybexinstitute/research/TruthOnFitness0912.pdf]
2. Hofmann (2013b) Are we mystified by the core? Part II [http://tmail.cybexintl.com/blog/docs/truthonfitness%20part%202.pdf]
3. Hofmann (2013c) Are we mystified by the core? Part III [http://media.cybexintl.com/cybexinstitute/research/TruthOnFitness0912.pdf]
4. Snarr and Esco (2014) Electromyographical comparison of plank variations performed with and without instability devices. J Strength Cond Res 28(11): 3298-3305.
5. Escamilla et al. (2006) EMG analysis of traditional and nontraditional abdominal exercises: implications for rehabilitation and training. Phys Ther 86(5): 656-671.
6. Vispute et al. (2011) The effect of abdominal exercise on abdominal fat. J Strength Cond Res. 25(9):2559-64.
7. Gallagher et al. (2000) Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. Am J Clin Nutrition 72:694-701.
8. Mitchell et al. (2012) Resistance exercise load does not determine training-mediated hypertrophic gains in young men. J Appl Physiol. 113(1):71-77.