The dead bug is a floor movement that asks your trunk to stay quiet while an opposite arm and leg move. Begin with a small range. The task is controlled movement, not reaching as far or as fast as possible.
Set your starting position
Lie on your back on a mat. Point both arms toward the ceiling and bend the hips and knees so the lower legs are roughly level. Settle your shoulders and breathe normally. The NASM movement demonstration shows this starting shape and the alternating reach.
Reach with opposite limbs
Slowly reach your right arm back and your left leg away. Stop before your lower back lifts or the movement becomes jerky. Bring both limbs back, pause, then try the left arm with the right leg. Exhale comfortably during the reach rather than holding your breath.
Keep the movement small
An arm or leg does not need to touch the floor. Shorten the reach if your ribs flare, pelvis tips or lower back arches. A slow return matters as much as the outward movement. Cleveland Clinic beginner core guidance also emphasizes movement quality over quantity for first attempts.
Try an easier version
Keep both knees bent and move only one arm, then reset. Or keep both arms vertical and extend only one leg a little. When each separate reach feels controlled, pair opposite sides again. Choose only a few comfortable alternating movements rather than a fixed target.
Compare related core moves
The bird dog on hands and knees also uses opposite limbs, but gravity and support feel different. A forearm plank hold asks for stillness instead of alternating reach. Use the beginner gym guide to place a floor movement in a wider session, and explore Fitonomy exercise discovery without assuming this exact exercise is listed there.
Stop when control fades
End the set when you cannot return smoothly or keep a comfortable back position. Stop for pain, dizziness, numbness or other concerning symptoms. Recent injury or movement restrictions call for individual advice. This exercise is not a treatment or a guaranteed way to prevent injury.