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Warming up before Wheel Pose (Urdva Dhanurasana): start with a gentle back and chest opener pose like Wild Pose (Camatkarasana) which will also help you gain arm strength required by the Wheel Pose. You can then try the Camel pose (Ustrasana) to open the back and the shoulders a little more. Remember not to rely on your lower back only, extending the upper back will make the poses more effective. Take these steps before moving on to ensure you build your strength