The barbell rollout is an advanced training exercise for the trunk for intermediate to advanced athletes. Unlike most bodyweight trunk exercises, the rollout is intense. It requires the trunk to be stabilized while you move your arms out and in.
The standing barbell rollout is too intense for most people, so they do it from the knees. But there’s one problem with the kneeling variation: people have their feet on the ground. This allows them to use the hamstrings when returning to the end position. Pulling with the hamstrings can lead to less activation of the trunk muscles. It’s counterproductive.
Avoid the engagement of the hamstrings by bringing your feet up and keeping them up during the rollout. This way, the hams can’t do any of the work and the trunk muscles have to do the heavy lifting.