Planks: What Muscles They Work and How to Do One

The versatile plank helps strengthen muscles of the arms, shoulders, back, core, and more, all in one move. It’s central to many exercise programs, from Pilates to yoga to circuit training, along with being a killer body weight–only move on its own.

“When you realize that a plank isn't just about your abs but also engages other areas, you start to focus on activating those muscles,” says Stephen Marcotte, National Strength and Conditioning Association (NSCA)–certified strength and conditioning specialist and senior manager of workout design and experience at Orangetheory Fitness in the Tampa Bay, Florida area.

The plank is an isometric body-weight exercise that boosts core endurance. (Isometric means that there’s no movement involved.)

The core includes the pelvic floor, obliques, transverse abdominals, rectus abdominals, and the erector spinae — the muscles along the backside of your trunk that help you stand up, as well as straighten your back while sitting.

But even though you’re not moving, your muscles (including ones other than the core) are working.

How Planks Strengthen the Abdominal Muscles

In a plank, you’ll predominantly be using the transverse abdominis and rectus abdominis muscles of the abdominal wall, says Cameron Yuen, DPT, CSCS, a doctor of physical therapy and practicing physical therapist at Bespoke Physical Therapy, a physical therapy practice in New York City, Seattle, and San Diego.

It’s the group of muscles on the front side of your abdomen: “The rectus abdominis is the most superficial muscle and creates the ‘six-pack look,’ while the transverse abdominis is the deepest abdominal muscle,” he explains.

But strong abdominal muscles are for more than aesthetics — they’re important for stabilizing the body, protecting your body’s inner organs, preventing low back pain, and aiding in virtually all body movements.

To see an improvement in abdominal strength, start by holding the plank for 20 seconds several times a week, maintaining good form the whole time, Marcotte says. Gradually increase your hold time as you get stronger.

How Planks Strengthen the Obliques

A plank works the obliques by tapping those muscles to keep the spine and torso stable throughout the move and to prevent rotating and sagging, Marcotte says.

The body has internal and external oblique muscles, which are located above the pelvic floor and run along the sides of the core.

These muscles are key to keeping your trunk steady during daily activities and helping the body twist and turn during rotational movements (just like they’re called upon when you hold a plank position), says Jamie Nuwer, MD, a board-certified family medicine physician with a certificate of added qualification (CAQ) in sports medicine with virtual health platform PlushCare in Dover, New Hampshire.

The obliques are important for full body stabilization, too, since the core muscles attach to the spine and keep the spinal column stable.

One variation in particular — the side plank — targets the obliques. “Planks that include rotation are also highly effective for engaging those side muscles,” Marcotte says. (More on rotational planks below.)

How Planks Strengthen the Back Muscles

Planks strengthen the upper, middle, and lower back muscles as they work to maintain proper spinal alignment and prevent the lower back from sagging or overextending, Marcotte says. “They work with your front (anterior) core muscles to create a solid, stable ‘bridge’ from your shoulders to your glutes,” he says.

Strong back muscles aid in body stability and play a role in every movement.
“Strengthening the back muscles helps keep your trunk stable during daily activities and also helps protect your spine from back injury,” Dr. Nuwer says.

And the reverse — strengthening the core — aids the back as well since a weak core contributes to lower back pain. That’s because when the core muscles aren’t pulling their weight, the body turns to other muscle groups, like the back, to compensate.

“Over time the nonmuscular components (like the ligaments, discs, and joints) start to develop degenerative changes that can lead to things like pinched nerves,” Nuwer says.

The best plank variation to help strengthen the back is the forearm plank (more on how to do one below) because you’ll generate more tension through the core and lats. The latissimus dorsi muscles are the large V-shaped muscles connecting your arms to your spine and back. “The key in this position is that the buttocks need to stay slightly elevated, otherwise it will put strain on the joints of the lower back,” Nuwer says.

If you’re currently battling back pain, the best plank for you is one where your body maintains a 45-degree angle, like a modified plank with your knees on the ground.

How Planks Strengthen the Shoulder and Arm Muscles

Think about what’s holding your body up when you’re in the plank position — it’s your shoulder and arm muscles. “Those muscles are the trapezius, rhomboids, latissimus dorsi, pectoralis, serratus anterior, and deltoids,” Nuwer says.

Engaging the large shoulder stabilizing muscles can help protect the shoulder and improve stability, she adds.

Planks are good to add to your arm strength workouts, too. The bicep and tricep muscles are attached to all of these other major arm and shoulder muscles, so they come into play, too, when you plank, Nuwer says.

To maximize upper body engagement, try the up-down plank. (More on how to do it below.)

To do a straight-arm plank:

Start in a push-up position with your elbows beneath your shoulders and only your hands and toes touching the ground.
Keep your palms flat on the ground and tuck your chin so your gaze is directed toward the floor, but don’t let your head drop.
Contract your glutes by tilting your pelvis forward slightly and engage your abdominal muscles so they are firm.
Draw your shoulder blades down your back, squeezing toward one another.

While holding the position, keep in mind that your body should be in a straight line from the crown of your head to your heels.
You should not feel an arch in your lower back — and you should not feel your butt sagging toward the ground or lifting in the air.

This can strain the lower back, Marcotte says.

It can be beneficial to know a few key plank variations and incorporate a variety into a comprehensive core workout. “Each type of plank challenges different muscles,” Marcotte says. “Mixing it up is a great way to build a balanced, stronger core while keeping your workouts engaging and effective.”

Try these plank variations:

Modified Plank For this one, keep your knees on the ground (the straight line your body forms should run from your head to your knees), which works the core, but is less challenging and a good starting point for beginners, Marcotte says. This is also helpful for those with a back injury.
Forearm Plank This variation works the muscles worked in a standard plank with a focus on the front core plus the gluteus maximus and quads, Marcotte says. Do it by following the directions for a standard plank, but instead of your hands being on the ground with arms extended straight, rest your forearms on the ground to support yourself (with elbows close to your sides and directly below the shoulders with your palms on the ground and hands pointing forward).
Side and Forearm Side Plank These variations work the oblique muscles and lateral core, Marcotte says. From the forearm plank position, turn to your right side and stack your right foot on top of your left foot (or place it just behind the left foot if you need extra balance). Lift your right arm straight in the air. Your left forearm and your left foot should be the only parts of your body making contact with the ground, and your body should form a straight line from the shoulders to ankles. Reverse the move to perform on your opposite side.
Rotational Plank This one puts an emphasis on obliques, Marcotte says. To do it, start in a plank position and lift your right arm as you rotate your body to the right. Stop when your arms are aligned with one another and form a line that’s perpendicular to the ground.
Single Leg Plank For this variation, start in a standard plank position. Then raise one leg at a time. This slight movement engages the leg muscles even more, Nuwer says.
Up-Down Plank This variation activates your arm muscles in addition to the core, Nuwer says. To do it, start from the forearm plank position, push up on one arm and then the other into a pushup position. Then, lower one arm and then the other so you’re back in the starting forearm plank.

Consider these tips for adding planks to your next workout:

1. Start on Your Knees

If you’re new to planking, start by planking on your knees (the modified plank variation). Hold for 20 seconds. When you’re able to hold for 30 seconds without sacrificing form, you may be ready to graduate to a standard plank, Marcotte says. Remember: It’s better to focus more on form than how long you’re able to hold at this point.

2. Make 1 Minute Your Baseline

Aim to hold a plank for between one and two minutes, Dr. Yuen says. “This isn't arbitrary, as this is roughly how long most exercise sets last, and you want your core to at least be strong enough to maintain a neutral spine for this amount of time, since this is when your spine is under the most load,” Yuen says.

3. Do (at Least) 1 Everyday

Plank every day if you want to. “Planks are low impact, so they can be incorporated into your routine regularly without putting too much strain on the body,” Marcotte says. “The key is to listen to your body — if you’re feeling sore, take a rest day.”

4. Add Variations

Consider adding one or two plank variations into a full-body workout. “Adding planks into a broader routine gives you a well-rounded approach, and many fitness plans encourage these combinations to build strength and stamina,” Marcotte says.

5. Up the Difficulty

Make it more challenging by placing a weight on your back (under someone else’s guidance for safety reasons), lifting one leg or arm, or putting your feet or your forearms on an exercise ball to make it more difficult to balance.
Or, reach over your head (one arm at a time), while planking, again challenging the body’s balance.

The standard plank is a great exercise that taps muscles in your core, obliques, back, shoulders, and arms. It requires no cost and no equipment, so you can really do it anywhere, any time. Hold for as long as you can, and you’ll benefit from a stronger core, which can aid with balance and everyday movements.

With additional reporting by Locke Hughes.

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