Side plank
- Muscle:
- obliques
- Equipment:
- bodyweight
Why it's worth doing
The side plank trains the obliques in the one plane of movement most ab exercises leave untouched: resistance to lateral trunk flexion. A crunch or a leg raise load the sagittal plane, forward and back, but neither demands anything when a force pushes the body sideways, which is exactly what the side plank does by holding the weight of the trunk against gravity from a single side.
That function, resisting the trunk bending to one side, is also one of the most used outside the gym: carrying a heavy bag on one side, twisting the torso to pick something up off the floor, or simply walking with an unbalanced backpack all depend on the same capacity this exercise trains directly and isometrically.
Being an isometric, no-load exercise also makes it one of the simplest to progress without equipment: changing the leg support point or the hold time is enough to make it harder or easier, which makes it accessible from someone's very first core session all the way up to fairly advanced levels.
How to do it
- Lie on your side with your legs extended, one on top of the other, and your forearm resting on the floor directly under your shoulder.
- Bend your elbow to 90 degrees and make sure it stays lined up under your shoulder, not out in front of it or behind it.
- Brace your abs and lift your hips off the floor until your body forms a straight line from head to feet, without your hips sagging down or piking up.
- Stack your shoulders and hips directly on top of each other, without rotating your torso forward or backward at any point during the hold.
- Keep your neck in line with your spine, looking forward, without letting your head drop toward your supporting shoulder.
- Hold the position breathing steadily, without holding your breath; prioritize the quality of the line over the total time.
- Lower your hips under control once the time's up and repeat on the other side, without assuming one side will hold as long as the other.
Watch the video
Muscles worked
The prime mover is the oblique on the supporting side, both external and internal, which contract isometrically to hold the weight of the trunk against gravity and keep the hips from sagging toward the floor. It's one of the few ab exercises where the obliques work as the star instead of stabilizing some other movement.
The quadratus lumborum, in the lower back on the supporting side, helps directly by holding the pelvis lifted, and it's usually the muscle that feels the most sore the next day for someone new to this exercise. The gluteus medius on the supporting side comes in as a hip stabilizer, keeping the pelvis from rotating forward or backward during the hold.
As additional stabilizers, the shoulder and rotator cuff of the supporting arm hold the weight passing through the forearm, and the core as a whole, rectus abdominis included, helps keep the trunk rigid so the straight line from head to feet doesn't break at any point.
Common mistakes
- Letting the hips sag toward the floor during the hold: it's the most common failure and the sign the muscle has hit its real limit.
- Rotating the torso forward instead of keeping the body in a single straight line from the side.
- Holding your breath to feel more stable: the gain lasts a few seconds and then forces you to exhale all at once.
- Setting the elbow forward or behind the shoulder: it changes the lever angle and takes tension off the obliques, handing it to the shoulder instead.
Side plank or front plank
Side plank or front plank is a real comparison, even though they train different planes of movement.
The front plank, propped on both forearms and the balls of the feet, facing the floor, mainly trains the rectus abdominis and resistance to lumbar extension: the strength that keeps the hips from sagging forward. It's a sagittal-plane exercise, the same plane a crunch or a leg raise works, just isometric instead of dynamic.
The side plank, by contrast, loads the frontal plane: it resists the trunk bending to one side, a stimulus the front plank never touches at all. Resting on a single forearm instead of two also demands more shoulder stability on that side and isolates each side of the body separately, something the symmetrical front plank won't reveal if one side is compensating for the other.
They aren't interchangeable: someone who only does front planks can have a strong core in the sagittal plane and a weak one laterally without noticing, until a real load, carrying something heavy on one side, exposes the difference. A well-trained core holds up in both, and programming them together, not one instead of the other, is what covers the full pattern.
Frequently asked questions
How long should I hold a side plank?
There's no universal number: the quality of the line matters more than the stopwatch. A reasonable starting reference is twenty to thirty seconds per side with good technique, adding time only while the hips stay aligned and breathing stays normal. The moment the hips start sagging or you have to hold your breath to hang on, that's the real limit, not whatever the clock says.
How do I progress the side plank as it gets easier?
The simplest progression is resting on bent knees instead of the feet, which shortens the lever arm and lowers the demand quite a bit; it's the starting point for anyone who can't yet hold the full version. From there you move to the version with the feet extended and stacked, the one on this page. The next step is lifting the top foot a few inches off the bottom one during the hold, which narrows the base of support and demands more from the obliques. Only after that does it make sense to add external weight, with a plate resting on the hip.
How should I breathe while holding a side plank?
Normally and continuously, without holding your breath. Holding your breath raises intra-abdominal pressure for a moment and can feel like more stability, but that strategy doesn't hold up for more than a few seconds and ends with the person exhaling all at once, right when the trunk most needs constant tension. Breathing evenly, even if a bit shorter than at rest, holds the position longer with less total effort.
Why do my hips sag toward the floor during the hold?
Because the obliques on the supporting side stopped generating enough force to hold up the weight of the trunk, and the hips give in to gravity. It's the most common failure in this exercise and the clearest sign the hold has already gone past what the muscle can sustain with good technique: at that point it's better to lower down and rest, not force a few more seconds with the hips sagging.
Similar exercises
Leg raises are the direct complement in the other plane of movement: they train the rectus abdominis through hip flexion, a pattern the side plank, focused on resisting sideways bending, never touches. Between the two, they cover most of what a core needs to hold up outside the gym: resisting the trunk bending forward, backward, and to one side.
Programming them in the same session doesn't compete for the same stimulus, so the order isn't critical; what does matter is not letting either one replace the other in the routine, since each exposes a weakness the other can't show.