Plank exercise: form, hold times and what it does for your back

What the plank trains

A plank is an isometric exercise: the muscles work without the joints moving. The deep and surface muscles of the abdomen, the obliques and the muscles along the spine all hold the trunk rigid, while the shoulders and hips keep the body off the floor. That is the same job the trunk does when you carry a suitcase, push a heavy door or stand on a moving train.

Trunk endurance can be measured. McGill and colleagues developed tests of the back extensors, the trunk flexors and the side bridge, a side plank on one forearm. In their study the tests proved highly reliable, with coefficients above 0.97 over five days and again eight weeks later. They also found different profiles by sex: men held the side bridge for 65% of their extensor time, women for 39%. The tests are useful for comparing you with yourself over time, more than with anyone else.

Plank form, step by step

1. Set the forearms. Elbows under the shoulders, forearms parallel or hands lightly clasped.
2. Step the feet back. Feet hip-width apart, toes tucked under.
3. Make one line. Heels, hips, shoulders and head in a straight line, as in the left-hand figure.
4. Brace. Tighten the abdomen as if bracing for a light punch, and squeeze the glutes.
5. Push the floor away. Keep the shoulder blades from sinking between the shoulders.
6. Breathe normally. Short, steady breaths. Do not hold your breath.
7. Stop when the line breaks. The set ends when the hips sag or rise, not when the timer says so.

How long to hold

No evidence-based target exists. McGill's normative hold times come from young, healthy adults and are not a goal for a 50-year-old executive. Several shorter holds with clean form are a coaching convention, and a sensible one: the quality of the position is what trains the trunk.

The calculator adds up holds and rests. Four holds of 30 seconds with 30 seconds of rest give two minutes of work in three and a half minutes. Holds of 20 to 60 seconds are a practical range for repeated sets. Below 20 seconds is fine to start. Beyond a minute, make the plank harder instead of longer, since a three-minute hold mostly tests patience.

The plank and back pain

The honest picture is modest. Saragiotto's review found that motor-control exercise improved long-term pain by about 13 points out of 100 compared with minimal intervention, with minor or no adverse events. But it was not better than other exercise, and the authors concluded that the choice should depend on preference, cost and safety. A broader 2021 Cochrane review by Hayden and colleagues found that exercise therapy in general reduces chronic low back pain. NICE recommends exercise programmes, in groups and of various kinds, for people with low back pain.

So a plank is a reasonable part of a routine for a sore back, alongside walking and strength work, but it is not a special treatment, and no study shows that core work prevents back pain. If you sit all day, the movement breaks in posture in long meetings matter at least as much.

Two claims to set aside

The first is that planks flatten the stomach. Vispute's trial found no reduction in abdominal fat from six weeks of abdominal exercise, and fat comes off the whole body, not the muscle you train. The toning principles guide explains what actually changes how a midsection looks.

The second concerns blood pressure. A large 2023 network meta-analysis by Edwards and colleagues found that isometric exercise training lowered resting blood pressure by about 8 and 4 mm Hg, more than any other mode, and an earlier analysis by Inder and colleagues found a similar effect. Those trials used handgrip, leg-extension and wall-squat protocols, not the plank. The effect cannot simply be transferred to planks.

Variations, easier and harder

• Easier: plank with the hands on a desk or a wall; plank from the knees; shorter holds of 10 to 15 seconds.
• Standard: forearm plank, then the straight-arm plank on the hands.
• Side plank: on one forearm, hips stacked, body in a line. Start from the knees if needed.
• Harder: lifting one foot or one arm for a few seconds at a time; plank with shoulder taps; feet on a step.
• Moving versions: dead bug and bird dog on the floor, which train the same control with the limbs in motion.

For comparison, an electromyography study by Escamilla and colleagues found the highest abdominal activity in exercises such as the roll-out on an ab wheel, the hanging knee-up and the reverse crunch on an incline. The plank was not among those tested. Muscle activity on a sensor also says nothing about long-term results, so variety matters more than the single best exercise.

A 20-minute office or hotel routine

1. Warm-up, 4 minutes. March on the spot, ten slow cat-and-camel movements on hands and knees.
2. Forearm plank, 4 minutes. 4 holds of 30 seconds, 30 seconds of rest.
3. Side plank, 5 minutes. 3 holds of 20 seconds on each side.
4. Dead bug, 4 minutes. 3 sets of 8 slow repetitions per side.
5. Glute bridge, 3 minutes. 2 sets of 12.

The plank fits at the end of a strength session too, after push-ups or the hip hinge, when the larger movements are done.

Precautions

Hold the plank only while your form stays clean, and keep breathing. With high blood pressure, avoid long efforts with the breath held, and ask your doctor before starting isometric work. Stop if your back hurts.

If you would like someone to judge the line of your plank, and to build the rest of the session around it, you can join the Club.