Every little (and big) muscle in your abdominals is engaged during boat or low boat pose. Low boat engages the transverse abdominals particularly well.
How to do it: Sit on the mat with your knees bent in front of you and your feet flat on the ground. Hold your arms, palms face up, in front of you so that your hands brush the sides of your knees. Lean back so that your torso is at a 45-degree angle to the floor. Slowly, lift your feet off of the ground as you straighten your legs, forming a “V” with your body. Use your core muscles to hold you in the position, and bring your arms slightly away from your body for more balance. Hold the pose for 10 counts.
For Low Boat: From boat pose, lower your middle back to the floor, keeping your abs engaged and your head and shoulders off the floor. Simultaneously lower your legs, so that your feet are about six inches off the ground. Engage your quads and abdominals (and breath!).