What is the primary action performed during reverse crunches?

The primary action performed during reverse crunches is pulling the knees into the chest while contracting the abdominal muscles. This movement specifically targets the lower abdominal region, engaging the core effectively as you lift your hips off the ground and bring your knees up towards your chest.

This exercise is designed to strengthen the abdominal muscles while minimizing strain on the lower back. By focusing on bringing the knees inward, the exercise emphasizes the action of the abs in a way that promotes strength and stability.

Other options describe actions that play different roles in core workouts but do not represent the main focus of a reverse crunch. For instance, extending legs outward or lifting shoulders off the ground could be part of other abdominal exercises but do not encapsulate the key movement intended in reverse crunches. Twisting the torso side to side introduces a rotating element that targets different muscle groups and is not a characteristic of reverse crunches, which focus straightforwardly on lifting the hips while pulling the knees in.