Is a BOSU Crunch harder than a floor crunch?

Not always. A study of 24 men doing sit-ups with a BOSU dome under the lower back found that with body weight alone, rectus abdominis activity was no different from the floor and external oblique activity was 22 to 24% lower, while with added band resistance rectus abdominis activity was 21 to 24% higher. The dome mainly adds range and a balance element, so add load once body-weight reps feel easy.

Which side of the BOSU should face up?

The dome faces up and the flat platform sits on the floor. You lie back over the curve of the dome, which supports your lower back.

How far should I come up?

The full rep finishes with the torso close to upright and the chest facing the knees. If your feet start to lift or you feel it mainly in the front of your hips, stop once your shoulder blades have cleared the dome.

Where should my hands go?

Crossing the arms over the chest is the easiest position and keeps you from pulling on your neck. Moving the hands lightly beside the head makes it harder, but they should only rest there, never pull.

How many reps should I do?

Two to four sets of 10 to 20 slow, controlled reps suit most people. When you can do 20 clean reps, slow the lowering phase or hold a light weight against your chest.

Can I do BOSU Crunches with lower back pain?

The dome supports the lower back, but repeated bending forward can still aggravate some back problems. If it causes pain, stop and use a bracing exercise such as the Dead Bug, and check with a clinician if the pain persists.

BOSU Crunch

What Is the BOSU Crunch?

BOSU Crunch is an isolation exercise that primarily targets the core, with the obliques and hip flexors assisting. It is a beginner-level movement performed lying back over the dome of a BOSU Balance Trainer, which supports the lower back and lets the torso start slightly reclined instead of flat on the floor.

The dome changes a floor crunch in two ways. The curved surface lets the trunk begin each rep a little further back, so the abdominals work through a longer range than when the shoulder blades rest on the floor. It also adds a mild balance demand, because the body has to stay centered on a surface that can shift slightly from side to side. The BOSU is more stable than a full exercise ball, which makes this a sensible first step before an Exercise Ball Crunch.

The rectus abdominis does most of the work as the ribs curl toward the pelvis, and the external obliques help flex the trunk and keep it from tipping sideways. As the torso comes close to upright at the top, the hip flexors take a larger share. Keeping the feet planted and the movement slow keeps the emphasis on the abdominals rather than on a heave from the hips.

The exercise suits beginners and general fitness clients who want a supported crunch with a bit more range, and it fits at the end of a session as core accessory work. Anyone who cannot yet control a standard Crunch on the floor should build that first, and people who find trunk flexion uncomfortable can train the core with bracing work such as the Dead Bug instead.

Muscles Worked

MuscleActivation

Rectus Abdominis: Primary
External Oblique: High
Rectus Abdominis (Lower): High
Rectus Femoris: Medium
Sartorius: Low
Sternocleidomastoid: Low
Tensor Fasciae Latae: Low
Adductor Longus: Minimal

Instructions

Place the BOSU on the floor with the dome facing up.
Sit just in front of it and lie back so your lower back and the top of your hips rest on the center of the dome.
Bend your knees to about 90 degrees and plant your feet flat on the floor, hip-width apart.
Cross your hands over your chest.
Start with your torso reclined along the dome, shoulders just above the floor and chin in a neutral position.
Exhale and curl up, bringing your ribs toward your pelvis and lifting your shoulders, then your upper back, off the dome.
Keep curling until your torso is close to upright and your chest faces your knees, with both feet still flat on the floor.
Inhale and lower slowly back to the start position under control.
Repeat for the desired number of reps.

Common Mistakes

Using momentum
Swinging up quickly and dropping back down lets momentum do the work that the abdominals should be doing.
Leading with the head
Jerking the chin toward the chest strains the neck, so curl up by bringing the ribs toward the pelvis and let the head follow.
Feet lifting off the floor
When the feet rise, the hip flexors are hauling the torso up, which is a sign to slow down or shorten the range.
Sitting off center on the dome
Sitting too high, too low or to one side makes you slide or tip, so set the lower back on the middle of the dome before the first rep.
Holding the breath
Holding the breath through the set makes it harder to control the rep, so exhale as you curl up and inhale as you lower.

Injuries

BOSU Crunch is a low risk exercise when performed with proper technique. The dome supports the lower back throughout, and the load is only the weight of the upper body. The most common complaints are neck tension from jerking the head forward and a pulling feeling in the lower back when the hip flexors take over near the top of the rep.

Keep the chin neutral and let the chest lead, not the head. Sit centered on the dome so you are not fighting to stay on it, keep both feet flat on the floor, and move slowly in both directions. If your feet lift or you feel the effort mostly at the front of the hips, shorten the range and stop once your shoulder blades have cleared the dome.

To make it easier, go back to a standard Crunch on the floor or train the core without spinal flexion using the Dead Bug. To progress, slow the lowering phase, hold a light weight plate against the chest, or move to the less stable Exercise Ball Crunch.

Stop if you feel sharp or pinching pain in the lower back, pain or tingling that travels into a leg, neck pain that does not ease when you relax the head, or dizziness. People with a current disc injury or pain that worsens with bending forward should get clearance from a clinician before doing repeated crunches.

Overview

Primary Focus: Core
Equipment: Balance trainer
Modality: Strength
Difficulty: Beginner

Alternative Exercises

Frequently Asked Questions

Q: Is a BOSU Crunch harder than a floor crunch?: Not always. A study of 24 men doing sit-ups with a BOSU dome under the lower back found that with body weight alone, rectus abdominis activity was no different from the floor and external oblique activity was 22 to 24% lower, while with added band resistance rectus abdominis activity was 21 to 24% higher. The dome mainly adds range and a balance element, so add load once body-weight reps feel easy.
Q: Which side of the BOSU should face up?: The dome faces up and the flat platform sits on the floor. You lie back over the curve of the dome, which supports your lower back.
Q: How far should I come up?: The full rep finishes with the torso close to upright and the chest facing the knees. If your feet start to lift or you feel it mainly in the front of your hips, stop once your shoulder blades have cleared the dome.
Q: Where should my hands go?: Crossing the arms over the chest is the easiest position and keeps you from pulling on your neck. Moving the hands lightly beside the head makes it harder, but they should only rest there, never pull.
Q: How many reps should I do?: Two to four sets of 10 to 20 slow, controlled reps suit most people. When you can do 20 clean reps, slow the lowering phase or hold a light weight against your chest.
Q: Can I do BOSU Crunches with lower back pain?: The dome supports the lower back, but repeated bending forward can still aggravate some back problems. If it causes pain, stop and use a bracing exercise such as the Dead Bug, and check with a clinician if the pain persists.