This simple floor exercise is redefining how Americans train their core—without crunches, machines, or strain on the spine.

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When it comes to core work, your abdominals should be engaged no matter what body part you are focusing on. That way, your body is ready for anything since your strength comes outward from the middle.

Think endless sit-ups are the secret to toned abs? Top trainers say you’re wasting your time — and there’s a smarter way to build real core strength.