The dead bug trains better control of the pelvis and spine to resist unwanted movement.
 
Lie on your back and crunch the abs to bring the tailbone and shoulders up off the floor. This crunched position needs to be maintained throughout the set—the point is to fight against the pelvis rotating forward as the legs extend and place tension on it.
 
Bring one straight arm overhead with the other at your side. Lift the opposite leg straight to vertical and keep the other flat with the heel off the floor. Maintaining the same ab tension and pelvic position, switch the arms and legs at a controlled tempo.
 
To scale the exercise, bend the knee to bring it up rather than keeping the leg straight. If further scaling is needed, keep both knees bent and simply lift the knee up toward the chest while keeping the feet off the floor.
 
Purpose
The dead bug is a good way to strengthen the ability of the abs to maintain a spine-pelvis relationship against forces trying to move them. It’s important that the spine is set in position and not allowed to move for the sake of straighter legs or greater range of motion or the purpose is defeated.
 
Variations
The dead bug can be done with straight legs to increase difficulty, or the range of motion shortened with bent knees to make it even easier. Small weights or bands can also be added.
 
Programming
The dead bug should generally be done for 2-4 sets of 5-10 or more reps per side. This is a good exercise for training preparation, or in addition to heavier, lower-rep or more difficult ab work in a given workout or in a circuit.