Side Plank Pose | Vasisthasana | Simple Yoga For Beginners | Mind Body Soulbr Side Plank Pose (Vasisthasana) is a powerful arm balance and core-strengthening yoga pose. This pose works your core to a huge extent. You have to really use your belly muscles to stay upright, so you'll definitely be feeling the core work the day after. It might not seem like it, but this is actually a good experience because you're developing your concentration skills! Once you come out of the pose, you'll feel like you can conquer anything.