Cross Body Knee Crunch
Also known as: cross knee crunch, lying elbow to knee crunch, alternating elbow to knee crunch
- Primary muscleAbs
- EquipmentBodyweight
- DifficultyBeginner
- TypeCore · Core flexion
- Secondary muscles
- Hip Flexors, Spine
- Body part
- Core
- Position
- Lying
- Laterality
- Bilateral (both sides together)
- Category
- Strength
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Each rep pairs an elbow-to-opposite-knee twist with the other leg extending and hovering off the floor, so one side rotates while the other resists the low back arching. That hovering leg separates it from the plain Cross Body Crunch and pushes it closer to a bicycle done one deliberate rep at a time.
How to do the Cross Body Knee Crunch
- Lie flat on your back with your knees bent and feet flat on the ground.
- Place your hands behind your head with your elbows pointing outwards.
- Engage your abs and lift your upper body off the ground, bringing your right elbow towards your left knee.
- At the same time, extend your right leg straight out and lift it off the ground.
- Pause for a moment, then return to the starting position.
- Repeat the movement, this time bringing your left elbow towards your right knee and extending your left leg.
- Continue alternating sides for the desired number of repetitions.
Tip: Breathe out as you crunch and let the last bit of air leave the lungs at the top of each rep.
Muscles worked
Primary
Abs · Core
The rectus abdominis shortens to bend the spine forward, and each rep should end with the upper abs fully contracted and the ribs pulled down.
Secondary
- Hip Flexors — The hip flexors take over if your feet are anchored and you come up too high; keep the range short to leave them out.
- Spine
Common mistakes
- Pulling on the neck — hands behind the head should support, not yank; keep the elbows wide and the chin about a fist away from the chest.
- Sitting all the way up — a crunch is a curl of the ribs toward the pelvis, not a sit-up; the lower back should stay on the floor the whole time.
- Cranking out fast reps — momentum does the work if you bounce; lift to a squeeze, hold for a count and lower slowly.
- Never adding load — once bodyweight reps get easy, hold a plate on the chest or use a cable rather than doing sets of 50.
Sets, reps and where it fits
| Goal | Sets × reps | Rest |
|---|---|---|
| Strength | 3 × 8–12 | 60 s |
| Endurance | 2–3 × 15–25 | 45 s |
Crunches close out a session after the heavy work, or they can fill the rest periods between sets of a lift that does not need much bracing. Pair a cable crunch with a cable side bend on the same stack.
Variations and alternatives
Similar exercises
Without bodyweight
Frequently asked questions
What muscles does the Cross Body Knee Crunch work?
The Cross Body Knee Crunch primarily works the abs. It also involves the hip flexors and spine, which assist the movement and stabilise the joints.
Is the Cross Body Knee Crunch good for beginners?
Yes. The Cross Body Knee Crunch is rated beginner: it uses no equipment beyond your bodyweight and the movement is simple to learn. Start light, focus on the full range of motion and add load once every rep looks the same.
What can I do instead of the Cross Body Knee Crunch?
If you cannot do the Cross Body Knee Crunch, try the Forearm Plank Pike, the Cocoon Crunch or the Flat Bench Knee Tuck. Each of them trains the abs through a similar movement, so you can swap them in without changing the rest of the workout.
How many sets and reps should I do?
It depends on your goal. For the Cross Body Knee Crunch, a sensible starting point is strength: 3 × 8–12 with 60 s rest; endurance: 2–3 × 15–25 with 45 s rest. Train it at the end of a session or pair it with a lower-body lift as active rest.
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