Fire Hydrants are a dynamic body weight exercise that strengthens your glutes and core and improves your hip mobility and rotation.
Start on all fours with your hands and knees about shoulder width apart, so you have a strong base. Your hands should be directly under your shoulders and your knees under your hips. Keep your chin tucked so you are looking down towards the floor, and engage your core so you are keeping a flat back. Lift your right knee up and out to the side so it is externally rotated. Once in this position, hold for 1-2 seconds at the top whilst focusing on maintaining a flat back, strong core and squeezing your glute muscles. Repeat on the same side for the instructed number of repetitions before switching.
How high you lift your leg is not important in this exercise. Try to avoid twisting your spine to get height and focus on keeping the glutes and core engaged.