Weighted Donkey Kick Back
Start on all fours with hands aligned with shoulder and a neutral back. While your leg is bent at a 90 degree angle, place a weight behind your knee. Flex your foot and bend your lower leg toward your thigh just enough to keep the weight in place. Squeeze your glutes to raise your leg into the air, holding at the top briefly befor lowering your leg. Keep core engaged throughout and move at a controlled pace.