Planks and Crunches are (almost always) a waste of time.
That was difficult to type because 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 effectively with that goal in mind. So let’s take a closer look at these two exercises, and discuss how you can more effectively train.
What are planks and crunches?
First, let’s accurately describe the exercises in question. They are both exercises limited by body weight, performed through a small, or no, range of motion at the lumbar spine.
In any exercise, specificity is king. 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.
For example, 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.
The degree to which an exercise is beneficial is dependent on two things:
- How does it stress the body?
- 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.
What is your fitness goal?
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).
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 is such that it can no longer produce sufficient force – not to the point of "I’m kinda tired, I think I will stop here."
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.).
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. Once you are able to do more than 50 crunches, you should look for an exercise that is challenges those muscles until you can only do them a couple of times, if strength is the goal. This holds true for any muscle or group of muscles, not just the abdominals.
This is a big buzz term in the fitness industry that has no real meaning, consistent definition (Hofmann, 2013a), or correlation to performance (Hofmann, 2013b). 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.
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.
Maybe you perform these exercises because you’d like an effective way to isolate the abdominals during training. 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).
Many runners advocate that these exercises are critical for increasing running performance. But many studies (Hofmann 2013b) 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.
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)!
Any movement will help contribute to weight loss, but should also be combined with an active approach to improving diet.
To have fun and challenge yourself
If you or a client finds these exercises fun, challenging, and interesting, by all means they should be integrated into a workout.
Train the core like any other muscle
The muscles of the trunk (the "core") should be trained just like any other muscle in the body. 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.
If you don't have access to equipment like this, keep in mind that exercises like planks and crunches will be limited to their ability to help you get to your ultimate fitness goals.
Cory Hofmann, MS
Senior Research Manager
Cybex Research Institute
- Hofmann (2013a) Are we mystified by the core? Part II
- Hofmann (2013b) Are we mystified by the core? Part III
- Snarr and Esco (2014) Electromyographical comparison of plank variations performed with and without instability devices. J Strength Cond Res 28(11): 3298-3305.
- Escamilla et al. (2006) EMG analysis of traditional and nontraditional abdominal exercises: implications for rehabilitation and training. Phys Ther 86(5): 656-671.
- Vispute et al. (2011) The effect of abdominal exercise on abdominal fat. J Strength Cond Res. 25(9):2559-64.
- 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.
- Mitchell et al. (2012) Resistance exercise load does not determine training-mediated hypertrophic gains in young men. J Appl Physiol. 113(1):71-77.
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