Dead bug
Muscles worked : Deep core (transverse abdominis) · Hips
How to do it
- Lie on your back, arms reaching towards the ceiling, hips and knees bent to 90°.
- Press your lower back into the floor and keep it there for the whole movement.
- Slowly lower one arm overhead and the opposite leg towards the floor, without touching down.
- Return to the start under control.
- Repeat on the other side.
Common mistakes
- Lower back lifting off the floor: a sign the range has gone too far.
- Moving too fast: you lose control and the core disengages.
- Holding your breath: keep breathing normally throughout.
Where you should feel it
A deep, continuous tension in the lower abdomen, below the navel. If the lower back arches or pulls, the range has exceeded what your core can hold: that is the stop signal, not a detail.
Range of motion
Lower the arm and leg only to the point where the lower back stays pressed to the floor. That point is personal and moves over the weeks — it, not the distance to the floor, is your unit of measure.
Tempo and breathing
Three to four seconds per repetition, never speeding up. Exhale as you extend, inhale as you return: the exhale mechanically helps keep the ribs down and the back flat.
What works, precisely
The transverse abdominis, the deepest muscle of the abdominal wall, acts like a belt stabilising the pelvis. The obliques resist the rotation the cross-body movement creates, and the rectus abdominis holds the ribcage down. The hip flexors work in control on the extending leg.
Movement mechanics
This is an anti-extension exercise: the core’s job is not to produce a movement but to prevent one — here, the lower-back extension caused by the weight of the limbs travelling away. The cross-body pattern adds a resistance to rotation.
Benefits
- Teaches what the core actually does — stabilise rather than flex — more clearly than any conventional abdominal movement.
- Works the lower back without putting it under compression, unlike repeated sit-ups.
- Carries over directly to walking and running, where opposite arm and leg already work in alternation.
Adapt and progress
- Easier : Move one limb at a time, arm alone or leg alone, keeping the other in position.
- Harder : Fully extend the leg just above the floor, slow down further, or hold two seconds in the low position.
- Move on when : When three sets of ten per side go by with the lower back never lifting and the leg extended a few centimetres off the floor.