Back strength and flexibility are both important for physie. This ‘cobra’ pose from yoga is a great gentle stretch for your lower back. Relax your neck and keep your heels together. When you’re comfortable with the cobra, slowly straighten your elbows, making sure you keep your shoulders down away from your ears. To increase the stretch even further, bend your knees and bring your toes towards the back of your head (knees slightly apart). Breathe!