Suppose you are interested in strengthening your core. In that case, you probably don't have to scroll too far to find a recommendation to do a plank. Crunches used to be all the rave, then planks, and now planks plus functional progressions are on-trend. (1, 2) Since planks remain a hot topic, let's start there.
Planks are known to "strengthen your body from head to toe." We've also been told that a strong core can help reduce low back pain, improve the ability to perform daily tasks, and enhance athletic performance (3). As a physical therapist and lifetime pursuer of fitness, these statements come as no surprise.
After years of prescribing planks to my clients, I've observed my share of eye rolls, grunts, and exasperated sighs. I've understood their hesitation to comply as I also felt the demand of this exercise. If I continue challenging myself and my clients in this way, I want to make sure that the effort is worth the reward.
Being schooled in evidence-based theories, I opened my laptop and went straight to Google Scholar for answers. Because I know that science is an ever-evolving book of recommendations and rules, I was curious about the status of planks. I was wondering, since crunches have been left in the dust, are planks on their way out too?
Before I share what I found, let's clarify which muscles make up the core. It is essential to realize that the core is much more than your "six-pack ."It expands from the bottom of your pelvis to the middle of your rib cage and includes your body's front, back, and sides. The following muscles are the primary muscles that are most often referred to when the core is referenced:
Pelvic Floor (PF)
Transverse Abdominis (TA)
Internal Obliques (IO)
External Obliques (EO)
Rectus Abdominis (RA)
Erector Spinae (ES)*
Lumbar Paraspinals (LP)*
*The erector spinae is a group of 3 muscles: the iliocostalis, spinalis, and longissimus. The "lumbar paraspinals" is a broader label that includes the erector spinae plus the multifidus and rotatores.)
To better bring these muscles to life, I recorded this short video clip for you.
Here's what I found when I scoured some research:
The plank exercise strengthens the core effectively. Greater muscle activation occurs when planking on unstable surfaces. (4)
Plank Type: Plank on elbows on the floor, with feet on dynamic cushions or inside a suspension trainer.
Core Muscles Tested: RA, O, and ES.
Year of Study: 2016
Applying an unstable condition to the lower limbs using a dynamic cushion is considered more effective during plank exercises than without. (5)
Plank Type: Plank on elbows on a mat, with a dynamic cushion under the elbows and then under the feet.
Core Muscles Tested: TA, IO
Year of Study: 2015
Performing planks on unstable surfaces effectively activates specific core muscles.
Plank Type: Plank on elbows on an exercise ball "stirring the pot" and high plank with feet on an exercise ball while extending one hip at a time. (6)
Core Muscles Tested: RA, EO, IO
Year of Study: 2017
Core muscle activation is greater during planks vs. crunches or full bent knee sit-ups. RA activation is greater in prone planks vs. side planks. LP and IO/EO activation are greater during side planks vs. prone planks. The most significant core activation occurred during prone planks on a ball with hip extension. (7)
Plank Type: Plank on the floor, on a ball, and side planks (full and modified)
Core Muscles Tested: RA, IO, EO, LP
Year of Study: 2016
I know, that was quite a bit of research jargon. Let me sum it up for you. Planks ARE an excellent core exercise. You will activate different core muscles depending on the plank variation you do. Side planks will incorporate more back muscles vs. prone planks. Planks on unstable surfaces such as a dynamic cushion or an exercise ball will activate more muscle fibers vs. regular planks on the floor.
Bottom line: Planks DO REALLY strengthen your core. Advancing to planking on unstable surfaces is definitely worth it as more core muscles get activated this way. Progressing your planks further to include functional movements such as kneeling with rotation is an excellent option to enhance strength and athletic performance. However, you must be able to do a proper plank with good form before you progress to anything more challenging.
Lee, Jin & Jeong, Kwanghyun & Lee, Hyuna & Shin, Jaeyeon & Choi, Jaelim & Kang, Seungbeom & Lee, Byoung-Hee. (2016). Comparison of three different surface plank exercises on core muscle activity. Physical Therapy Rehabilitation Science. 5. 29-33. 10.14474/ptrs.2016.5.1.29.
Do YC, Yoo WG. Comparison of the thicknesses of the transversus abdominis and internal abdominal obliques during plank exercises on different support surfaces. J Phys Ther Sci. 2015;27(1):169-170. doi:10.1589/jpts.27.169
Youdas JW, Coleman KC, Holstad EE, Long SD, Veldkamp NL, Hollman JH. Magnitudes of muscle activation of spine stabilizers in healthy adults during prone on elbow planking exercises with and without a fitness ball. Physiother Theory Pract. 2018 Mar;34(3):212-222. doi: 10.1080/09593985.2017.1377792. Epub 2017 Sep 18. PMID: 28922049.
Escamilla RF, Lewis C, Pecson A, Imamura R, Andrews JR. Muscle Activation Among Supine, Prone, and Side Position Exercises With and Without a Swiss Ball. Sports Health. 2016;8(4):372-379. doi:10.1177/1941738116653931