Start this move by kneeling on all fours with your hands beneath your shoulders and your knees directly below your hips. Tighten your core muscles and slowly lift your right arm and extend it straight forward. Slowly lift your left leg and extend it straight back, with your toes pointed down. Hold for 10 seconds and slowly lower to starting position. Repeat three times on each side. If this movement is too advanced, try the easy modifications of this movement, lifting just an arm (lower left photo) or just a leg (lower right photo). Hold for 10 seconds and slowly return to starting position. Repeat three times on each side.