30 Alternating toe touches (15 per side)
This exercise also targets the obliques, but will challenge your entire core, including your hip flexors. Make sure you protect your lower back throughout by keeping it tight and engaged with the floor.
Start lying back, your arms extended over your head, your legs extended fully. In one movement, lift your right leg up off the ground, extending it directly over your hips as you simultaneously reach your left hand up to touch your right toes, focusing on tightening your core and using your abdominals to lift your arm toward your foot. Return to the fully extended lying position, then repeat on the opposite side.