Side Plank Crunch
What Is the Side Plank Crunch?
Side Plank Crunch is a compound exercise that primarily targets the core, especially the obliques, and also engages the glutes, hip flexors and supporting shoulder. It is an intermediate-level movement that starts from a forearm Side Plank and adds a crunch, drawing the top knee and top elbow toward each other while the hips stay lifted.
The exercise trains the side of the trunk in two ways at once. The bottom side has to hold the hips up against gravity for the whole set, while the top side shortens through each crunch, so the obliques work both to resist side bending and to produce movement. The static side plank this exercise is built on is a well-established lateral core exercise, and an EMG study of 30 healthy adults found that the side bridge activated the external oblique and gluteus medius strongly enough to be used for strengthening those muscles, not only for endurance.
Moving the top leg is what makes this harder than a plain hold. As the knee comes forward, the hip flexors of the top leg do the lifting, the rectus abdominis helps curl the ribs toward the pelvis, and the pelvis tends to roll or sag, so the bottom-side obliques and glutes have to work harder to keep the body stacked. The supporting shoulder also has to stay stable under a load that shifts with every rep. A bent-knee version with the bottom knee on the floor shortens the lever and makes the hold easier, while a straight-arm version on the hand raises the body higher and asks more of the shoulder and wrist.
It suits anyone who can already hold a steady side plank with level hips and wants a more dynamic oblique exercise, and it usually sits in the core block near the end of a session. If the hips drop as soon as the leg moves, build up with the Side Plank hold first, aiming for around 30 seconds per side with a straight body line, then practice controlled transitions with Plank to Side Plank. Focus on feeling the side of the waist shorten on each crunch rather than on how far the knee travels.
Muscles Worked
- External Oblique
- Primary
- Gluteus Medius
- High
- Rectus Abdominis
- High
- Deltoid
- Medium
- Rectus Abdominis (Lower)
- Medium
- Rectus Femoris
- Medium
- Tensor Fasciae Latae
- Medium
- Sartorius
- Low
Instructions
- Lie on your side with your forearm on the floor, elbow directly under your shoulder, and your legs straight with your feet stacked.
- Place the fingertips of your top hand lightly behind your head, with the top elbow pointing toward the ceiling.
- Press your forearm and the edge of your bottom foot into the floor and lift your hips until your body forms a straight line from head to feet.
- Brace your core and keep your hips stacked, without letting them sag or roll forward.
- Bend your top knee and draw it forward and up toward your chest while bringing your top elbow down to meet it, crunching through the side of your waist.
- Bring the elbow and knee as close as you can without letting the bottom hip drop, and pause briefly.
- Slowly straighten the top leg back onto the bottom leg and return the elbow to the start.
- Exhale as you crunch and inhale as you return. Complete all reps, then switch sides.
Common Mistakes
Letting the hips sag
Dropping the bottom hip toward the floor as the knee comes in takes the load off the obliques and glutes and puts it on the lower back and shoulder.
Pulling on the head
Yanking the head forward with the top hand strains the neck instead of crunching through the side of the waist.
Rolling the hips forward or back
Letting the pelvis and chest twist toward the floor or the ceiling breaks the stacked side plank line and turns the crunch into a loose twist.
Elbow drifting from under the shoulder
Placing the supporting elbow far from the shoulder or sinking into the shoulder joint loads the shoulder more and makes the hold less stable.
Swinging the knee
Kicking the knee up with momentum shifts the work away from the core and makes it harder to keep balance.
Injuries
Side Plank Crunch is a low risk exercise when performed with proper technique. The body is supported on one forearm and the edge of one foot, so the main strain points are the supporting shoulder, the neck, and the lower back if the hips sag or twist. The bottom hip, knee and ankle also carry load through the side of the leg, which some people find uncomfortable on a hard floor.
Keep the supporting elbow directly under the shoulder and press the forearm into the floor so the shoulder does not sink toward the ear. Rest the fingertips of the top hand lightly behind the head and never pull on it, since yanking the head forward strains the neck rather than working the trunk. Move slowly, and end the set as soon as the hips start to drop or roll, because that is when the lower back and shoulder begin to take the load. A mat under the forearm and hip makes the position more comfortable.
To regress, drop the bottom knee to the floor with the knee bent, which shortens the lever, or rest the forearm on a sturdy step so the body is more upright. If moving the leg is still too much, hold a static Side Plank until you can keep a straight line for around 30 seconds per side. To progress, add a pause at the top of each crunch, slow the return, or perform the movement from a straight-arm side plank on the hand.
Stop if you feel sharp or pinching pain in the supporting shoulder, the neck, the lower back or the bottom hip. Shoulder discomfort often eases with the elevated or bent-knee version, and pain that persists despite good form is worth having checked by a physical therapist or physician.
- Primary Focus
- Core
- Equipment
- Body weight
- Modality
- Strength
- Difficulty
- Intermediate
Alternative Exercises
Other Names for the Side Plank Crunch
The Side Plank Crunch is also known as:
- Side Plank Knee to Elbow
Frequently Asked Questions
- Q: How is the Side Plank Crunch different from a regular side plank?
A regular Side Plank is a static hold, while the Side Plank Crunch adds a moving top arm and leg. Each crunch adds hip flexion and a shortening of the top side of the trunk, and the moving leg makes it harder to keep the hips level, so most people need a solid side plank before this version feels controlled.
- Q: Is this the same as an oblique crunch or a cross-body crunch?
No. The Oblique Crunch and the Cross-Body Crunch are done lying on the floor with no body weight to support, while the Side Plank Crunch is performed in a side plank, so the bottom side of the trunk, the glutes and the supporting shoulder hold the body up the whole time.
- Q: How many reps and sets should I do?
2 to 3 sets of 8 to 12 slow reps per side is a common starting point. Finish all reps on one side before switching, and end the set when the hips start to drop rather than chasing a number.
- Q: What if I can't keep my hips up while moving my leg?
Drop the bottom knee to the floor and do the crunch from a bent-knee side plank, or go back to holding a static side plank until you can keep a straight line for around 30 seconds per side. Both build the hip and oblique strength the full version needs.
- Q: Can I do it on my hand instead of my forearm?
Yes. A straight-arm side plank raises the body higher and asks more of the shoulder and wrist, so it works as a progression once the forearm version feels steady.