While the plank and crunch both work the abs, each one does so uniquely. The plank requires an isometric contraction, or static holding, of the spine, whereas the crunch requires spinal flexion.

Primary muscles used in the crunch include rectus abdominis, the six-pack muscles, and obliques, similar to the muscles used in plank.

However, planks also activate muscles in the shoulders, glutes, and legs too. Research by The Pennsylvania State University shows that abdominal and lumbar muscles are activated more in exercises that require simultaneous activation of the deltoids (shoulders) and glutes.

I recommend plank over crunches for overall strength training.

Plank is a great core strengthening exercise to tone various parts of your body including your abs, back, and shoulders. It is one of the most complete total-body exercises there is and works multiple muscle groups simultaneously just by holding the isometric hold position for 30-60 seconds. It’s unbelievably simple and easy that almost anyone can perform, yet its super effective at developing core strength.

Here are the top 4 plank benefits:

Toned abs: Contrary to crunches that focus on the six-pack muscles (outer abdominal muscles), plank works the deep inner core muscles that function as base of the six-pack muscles. To see definitions in your abs, working the deep inner abdominal is a must.

However, be cautioned that your abs will start showing when your body fat percentage goes below 20-22% depending on your age and body type.

Stronger Back: According to the American Council on Exercise (ACE), plank exercise is a great way to build back strength and reduce back pain. Because plank requires minimal movement while contracting all layers of the abdominal fascia, it is an excellent way to strengthen the core, which, in turn, helps reduce low-back pain.

Improved flexibility: Planks also increase the flexibility in posterior muscle groups by working the shoulders, collarbone, and upper back and improves their strength and flexibility. These areas are often neglected with crunches.

Better posture: During the isometric hold, deep core stabilizing muscles such as transverse abdominis and iliopsoas and other nearby muscles get contracted simultaneously to stabilize and enable the straight body alignment. This activation of stabilizing muscles improves your stability and leads to better posture.

Despite all the great benefits and hardly any hurdle to perform this simple workout, planks are not to be taken lightly. Numerous studies have found that it’s better to maintain proper form for a shorter period of time than to hold improper form for longer. The smarter and safer way to advance your planks and challenge your core is to perform more advanced planks. This forces your body to engage your stabilizing muscles, even more, to hold the isometric position and resist the urge to drop your hips.