AKA Ab wheel, evil wheel
Hold an ab-wheel or barbell with rotating sleeves with straight arms either kneeling or standing depending on your strength, the wheel close to the knees or feet. Forcefully contract the abs to create a crunched, hollow position and maintain this throughout the motion—avoid hyperextension of the lower back.
Roll the wheel out until your body is as straight and close to the ground as possible, then roll back to the starting position, leading by crunching the abs and hinging at the hips.
The ab rollout strengthens the abs isometrically to better control the relationship of the pelvis and spine, and strengthens the hip flexion.
Ab rollouts should be done for sets of 10-30+ reps.
Slower tempos, static holds in the extended position, and multiple partial recoveries from the bottom each rep before recovering completely to the starting position can be added.