I have also referred to these as Mustangs, Hippogriff, or Donkey Kicks. Position yourself on all fours. Brace your core and keep your balance while lifting your right leg out behind you and up toward the sky. Bring knee toward chest and repeat the cycle with your right leg the number of repetitions. Once finished, then repeat the process with your left leg. For advanced modification, place a weight on the inside of your knee and hold it with your leg muscles while kicking leg up.