In fact, the Jefferson curl is more of a mobility exercise that strengthens the muscles of the lower back and core, as well as stretching the hamstrings, to help build a more resilient spine.
Your core is an interconnected group of muscles, not just your abs, that’s important to strengthen to support your body during exercise as well as everyday tasks.
And because your core wraps around the entire midsection of your body, it also includes your side waist, pelvic floor and lower back muscles ... Almost every exercise imaginable requires core ...