In this bird dog variation, you'll keep three points on the ground as you extend one leg at a time. Set up in a tabletop position and engage the lower core to keep your hips level as you extend one leg, returning to tabletop before alternating to the other side. Many folks have a tough time with controlling the pelvis and lower back when extended the leg straight, so try starting with your toe sliding on the ground or just hovering, then bring the leg closer to parallel as your control progresses.