Start in a push-up position with your hands under your shoulders and your body in a straight line from head to heels. Brace your core, then raise one arm straight out in front of you while lifting the opposite leg behind you, until both are level with your torso. Hold for a moment, return to the plank under control, then switch sides. The goal is to keep your hips square to the floor the entire time - nothing moves except the working arm and leg.

Works: abs, obliques, lower back, glutes, shoulders

Breathing: Exhale as you extend the arm and leg, inhale as you return to the plank - slow and controlled, in time with the movement.

Common Mistakes: Letting the hips tilt or rotate toward the raised side, kicking the leg higher than your torso and arching the lower back, and rushing through the switch instead of pausing at full extension.

Make Easier: Raise one limb at a time - Plank Arm Raises or Plank Leg Raises - until you can keep your hips steady, or perform the movement from your knees.

Make Harder: Hold each extension for a slow three-count before switching, or move on to Body Saw or Side Plank Rotations for even more core control.