Muscles Contraction During Plank Exercise

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The plank exercise can be performed with front or side variations.
Image Credit: Oliver Rossi/Stone/GettyImages

In recent years, planks have become the go-to abdominal exercise of choice, and for good reason. All your core muscles are used in a plank, along with a few muscles you might not expect.

Master Plank Basics

The most common plank variation is the front plank, done facing down toward the ground. It can be done on your forearms or on your hands as if you were holding the "up" position of a push-up:

  1. Position yourself on your hands and knees, and then extend your legs behind you so that you're balanced on your hands and the balls of your feet.
  2. If you prefer, you can bend your arms and place your forearms flat on the ground.
  3. Squeeze your core muscles to keep your body in a straight line from head to heels. Your hips should neither pike up nor sag down.

Having a mirror for reference, or a friend to check your form, is helpful until you get the feel of where your body should be.

Read more: The 4-Week Plank Challenge

Muscles Used in a Plank

There's no arguing that the plank is an excellent exercise for your entire core — although there are still a few glitches in the hunt to quantify just how good it really is.

As noted in the May 2011 issue of Medicine and Science in Sports and Exercise, a landmark EMG study of 14 participants found that forearm plank variations required more than twice the average activity of the rectus abdominus, external obliques and lumbar erector spinae when compared to traditional trunk flexion exercises.

And those aren't the only muscles used in a plank. In addition to your abs and erector spinae, you must also contract your glutes, deltoids, muscles, thighs, calves, latissimus dorsi and chest muscles to keep your body in that plank position.

Interestingly, a 2014 EMG study sponsored by the American Council on Exercise, with a field of 16 volunteers, found that the front plank elicited less activity in the rectus abdominus than the traditional crunch (the classic example of a "traditional" trunk flexion exercise).

One of the most common explanations attributed to discrepancies of data like this is that the instructions for doing these core exercises are not standardized between studies. The ACE study also did not look at some of the more difficult plank variations used in the Medicine and Science in Sports and Exercise study, including planks on stability balls with added hip extension.

Introduce Some Plank Variations

Changing up how you do your planks places emphasis on different muscles. For example, in the July 2016 issue of Sports Health, researchers used EMG testing to measure muscle activity as 18 subjects performed a variety of core exercises (including several types of planks) in different positions.

Unsurprisingly, they found that prone (facedown) exercises like the usual forearm plank generated significantly greater activity in the rectus abdominus, while activities like the side plank generated more activity in the external obliques. The internal obliques and latissimus dorsi were more active during front planks on a stability ball.

Adding variations to your planks can also ensure that you keep building core strength and stability as your body gets stronger; after all, if you stop challenging your body, it will no longer need to adapt by building greater strength and endurance. Those variations also help break up the monotony of what is, to some people, a boring exercise. A few variations you can try include:

Although planks are generally considered a mild core exercise thanks to their isometric nature (i.e., you do not flex or extend your spine during the plank), a thoughtful discussion by the American Council on Exercise notes that isometric exercises aren't ideal for everybody, because they can increase your blood pressure.

That sort of issue — as well as concerns like diastasis recti or back problems, which both can affect your ability to do core exercises — is why experts always recommend having a quick chat with your doctor before beginning a new exercise program.

Read more: The One Plank Variation Your Ab Workout Has Been Missing

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