If you are unfamiliar with the bird dog exercise, it is a fairly simple core exercise that is great for your posture because it encourages a neutral and stable spine. Furthermore, it challenges your core strength as you aim to resist both extension and rotation.
Once you get a hand of the bird dog it can feel like a pretty simple exercise. Below is a great variation that adds a little band resistance into the mix.
This exercise is known as the bird dog with band pull. Your goal is to be explosive and touch your elbow with your opposite side knee.