Planks vs. Crunches

In order to adequately compare the crunch exercise to the plank, we should address what the purpose of each exercise is. While one is meant for stabilizing and endurance for multiple muscle groups, the other is great for increasing specific muscle engagement. The benefit of each has their specific purposes and muscles that are involved.

In the plank, the muscles involved are primarily the transverse abdominus, rectus abdominus, internal and external oblique. The other accessory muscles involved are your (shoulders) deltoids, (backside) glutes, (chest) pectoralis major, (lower back) quadtratus lumborum and erector spinae. The isometric contraction activates the core muscles on the front side and back side of the body almost equally.

When considering the crunch, take into account the primary muscle group involved. The rectus abdominus is the primary muscle group activated when performing the typical crunch exercise. Running down the center of the body, the rectus abdominus is your six-pack with the origin at the pubic symphysis/crest and the insertion at the xyphoid process. Exercises and motions that create contraction while bringing the origin and insertion closer together engage the rectus abdominus best to create your dream six pack.

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The long-winded debate about whether the crunch or plank is better is yet to be decided. Form plays a large part in which will negatively or positively affect your spine. Crunches are a repetitive flexion and extension motion of the spine which can potentially aggravate a sensitive lower back.  Some ways to combat that are to perform proper form:

• Maintain a spinal alignment with the head and neck. This decreases full spinal flexion that often occurs from tucking the chin to the chest when straining to come up.
• Flatten your lower back to the floor. Pelvic bracing (contracting your abdominal muscles completely), helps to flatten your lower back to be more congruent with the floor, stabilizing the lumbar spine.
• Don’t come up too far. The further you come up, the more you involve your hip flexors.  Muscles that don’t strengthen your abs and put a strain on your lower back.
• Some options for alternative form for the crunch is a modified crunch where one leg is fully extended, the other knee bent, and hands lightly touching the sides of the head while gently rising from the ground in a modified crunch.

Planks are a safe isometric hold for most individuals with lower back problems. The less range of motion you have to move through tends to be slightly less aggravating on the lower back. By performing proper form in a plank, aggravation can be mostly avoided. Here are some form tips to help prevent low back pain in a plank:

• Imagine drawing your belly button to your spine.
• Contract your glutes consistently throughout the position.
• Keep your feet shoulder width apart.
• Maintain your elbows directly below your shoulders.
• Modified planks can be performed from the knees if low back pain is still present in the plank.

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Simply speaking, the plank involves a plethora of large muscle groups that are not specific muscles designed to help one develop a six pack, rather create a flooring effect to strengthen more muscles at once. The crunch takes the rectus abdominus through a specific range of motion to isolate and strengthen that muscle almost completely while not involving other motions. Crunches are good for avoiding stress to the spine when performed properly.

The reality of both of these exercises is that they help to develop your core but are designed for different goals. When performing a core exercise, consider the benefit of what you are doing in relation to your fitness goals in order to decide which exercise is appropriate for you.

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References:

Catalyst University. (2020, February 4). Abdominal Muscles | Origins, Innervations, Actions.

Mace, S. (2018, January 26). To Plank or Not to Plank. SamMace.

Want a Stronger Core? Skip the Sit-ups. (2020, July 2). Harvard Health Publishing.