What does the BOSU add compared with a regular cable side crunch?

The dome moves under you, so your trunk, hips and legs have to keep the seat steady while the obliques work. That makes the movement more about control, and it means you will use less weight than you would on a stable surface.

Which side does it work?

It mainly works the obliques on the side nearest the cable, because they pull your ribs down and across against it. Do the same number of reps with the machine on each side.

Will training my obliques with weight make my waist wider?

Not noticeably for most people. The obliques are thin muscles and moderate loads for 10 to 15 reps add very little width, while body fat has a far bigger effect on waist size.

How many sets and reps should I do?

Two to three sets of 10 to 15 slow reps per side work well near the end of a session. Pick a weight you can control at the top of every rep without the dome rolling.

Can I do this if I have lower back pain?

It depends on what aggravates your back. Twisting and bending under load bothers some people, so start with non-moving work such as the Side Plank or Cable Pallof Press and check with a clinician if pain persists.

Cable BOSU Side Crunch

What Is the Cable BOSU Side Crunch?

Cable BOSU Side Crunch is an isolation exercise that primarily targets the core, especially the obliques on the side closest to the cable, and also engages the rectus abdominis and hip flexors. It is an intermediate-level movement that combines a low cable pull from the side with a reclined seat on the dome of a BOSU balance trainer.

You sit on the dome with your knees bent and feet on the floor, lean back, and hold a single handle beside your hip with the hand nearest the machine. The cable tries to pull that hand, and your torso, back toward the weight stack. Each rep you curl your near-side ribs down and across toward the opposite hip, then let the cable draw you back under control. The cable keeps tension on the obliques through the whole rep, and the load can be raised in small steps, which bodyweight side crunches cannot offer.

The BOSU adds a second job. Because the dome gives under you, your hips, trunk and legs have to keep the seat steady while the obliques do the crunch. That makes the movement a good fit for trainers who want loaded oblique work that also asks for control, and for clients who have outgrown floor side crunches. The trade-off is that the unstable seat limits how much weight you can handle, so it is an accessory movement placed near the end of a session rather than a main strength builder.

It suits people who can already hold a side plank and do a standard crunch with control. If the dome and the cable together are too much at first, learn the pattern with a Cable Side Crunch on a stable surface, or build the obliques with a Side Plank before adding load. Focus on feeling the near-side ribs move toward the opposite hip, since it is easy to let the arm pull the handle instead.

Muscles Worked

MuscleActivation

External Oblique: Primary
Rectus Abdominis: High
Rectus Abdominis (Lower): Medium
Rectus Femoris: Medium
Erector Spinae: Low
Latissimus Dorsi: Low
Sartorius: Low
Tensor Fasciae Latae: Low
Flexor Carpi Radialis: Minimal
Gluteus Medius: Minimal

Instructions

Set a pulley at the lowest position and attach a single handle.
Place a BOSU flat side down beside the machine, about a leg's length out, and sit on the center of the dome with the machine to one side.
Bend your knees and plant your feet flat on the floor, about hip width apart, in front of you.
Take the handle in the hand nearest the machine and hold it beside that hip with a slight bend in the elbow. Rest your other hand on your far knee.
Lean back until your torso is at about 45 degrees and brace your abs. The cable should be pulling your near hand toward the stack.
Exhale and crunch your near-side ribs down and across toward your opposite hip, turning your chest slightly away from the machine so the handle moves from beside your hip toward the front of your hips.
Keep your arm fixed at your side and your chin slightly tucked. Let your torso move the handle, not your arm.
Pause briefly, then inhale and slowly let the cable draw you back to the starting lean.
Complete all reps on one side, then turn around so the machine is on your other side and repeat.

Common Mistakes

Pulling with the arm
Tugging the handle with the arm and shoulder turns the rep into a row, so keep the arm fixed at your side and let the ribs move the handle.
Using momentum
Swinging through fast reps lets the cable and your body weight do the work, so move slowly and control the return toward the stack.
Leading with the head
Jutting the chin forward strains the neck without adding any work for the obliques.
Chasing a big twist
Forcing a large rotation shifts stress to the lower back, so keep the crunch short and compact.
Unstable foot position
Feet set too close together or too far forward let the dome roll, which ends the set in a loss of balance rather than oblique fatigue.
Going too heavy
A weight that drags you back toward the stack before the crunch is finished is too heavy for the unstable seat.

Injuries

Cable BOSU Side Crunch is a low risk exercise when performed with proper technique. The load is modest and the range is short, but the movement combines trunk flexion with a slight twist on an unstable seat, so the lower back, the neck and your balance are the points to watch.

The lower back takes strain when the weight is too heavy and you yank through a large, fast twist instead of a controlled crunch. Keep the range small, move slowly and choose a weight you can hold still at the top of each rep. Tuck your chin slightly and let the ribs lead so the neck does not pull the head forward. Set the BOSU on a non-slip floor with the flat side down, and plant your feet wide enough that the dome cannot roll out from under you.

If the pattern is new, start with a Side Plank or a Cable Side Crunch on a stable surface, then move to the BOSU with a light weight. Progress by adding weight in small steps or by bringing the feet closer together to make the seat less stable, never both at once. Stop the set if you feel sharp or pinching pain in the lower back, pain that travels into a leg, or if you lose your balance on the dome.

Overview

Primary Focus: Core
Equipment: Cable and balance trainer
Modality: Strength
Difficulty: Intermediate

Alternative Exercises

Frequently Asked Questions

Q: What does the BOSU add compared with a regular cable side crunch?: The dome moves under you, so your trunk, hips and legs have to keep the seat steady while the obliques work. That makes the movement more about control, and it means you will use less weight than you would on a stable surface.
Q: Which side does it work?: It mainly works the obliques on the side nearest the cable, because they pull your ribs down and across against it. Do the same number of reps with the machine on each side.
Q: Will training my obliques with weight make my waist wider?: Not noticeably for most people. The obliques are thin muscles and moderate loads for 10 to 15 reps add very little width, while body fat has a far bigger effect on waist size.
Q: How many sets and reps should I do?: Two to three sets of 10 to 15 slow reps per side work well near the end of a session. Pick a weight you can control at the top of every rep without the dome rolling.
Q: Can I do this if I have lower back pain?: It depends on what aggravates your back. Twisting and bending under load bothers some people, so start with non-moving work such as the Side Plank or Cable Pallof Press and check with a clinician if pain persists.