An often end-of-class asana, the Boat pose (Navasana), challenges the strength of your core and hip flexors. Core strength radiates around the entire torso, not just those six-pack stomach muscles that are often focused on with crunches and sit-ups. Instead, the abdominal wall, the obliques (internal and external), and the erector spinae muscles all receive love and attention when practicing the boat pose.
Be gentle with yourself if you’re new to Boat. Modify as needed.