This tri-planar exercise adds a transverse-plane component to the sagittal-plane modified curl-up and the frontal-plane side plank. When done properly, bird dog is surprisingly difficult because it poses balance and postural challenges.
• Start in quadruped position.
• Reach one arm forward and opposing leg straight back.
• Align lead arm, head, hips and leg.
• Hold for 10 seconds then switch sides, performing 3 sets per side.