Kneel on the floor with a loaded barbell in front of your knees.
Grasp the barbell using a narrow pronated (overhand) grip.
Lean over the barbell so that it supports your upper body.
Execution
Keeping your elbows slightly bent, inhale as you gently roll out for as far as you can maintain a straight back.
Exhale as you reverse the movement and roll back in to the starting position.
Repeat.
Comments and tips
Keep the movement slow and deliberate.
Don’t allow your lower back to sag, which is bad for your lumbar spine. If your lower back keeps sagging, you are rolling out too far. To help keep your lower back straight, contract your abs. The more you practice the barbell rollout, the farther you’ll be able to roll out without letting your lower back sag.
Since there is usually very little or no flexion of your waist, and since most of the movement occurs in your hips and shoulders, the barbell rollout shouldn’t be labeled as an ab exercise. The abs do get a great workout, but they often only contract isometrically to stabilize the torso.
To make the barbell rollout more difficult, you can either add more weight to the barbell, wear a weighted vest, or load a chain around your torso. You can also perform the exercise on foot instead of on your knees; however, this is a very advanced variation (standing barbell rollout).
The barbell rollout (and other rollout exercises) is among the most effective exercises for developing anterior core strength and stability. As such, it is highly recommended.
Instead of a barbell, you can use a rollout wheel or a stability ball. The stability ball variation is easier for beginners.