Resisted clams shell ("Clamshell" Hip external rotation strengthening, with band; 03)

Lie on your side with your legs bent and stacked on top of each other.
Tie a resistance band around your knees and activate your core stability muscles.
Keep your feet together and lift your top knee taking care not to allow your body to roll backwards and then lower back to the starting position.
Control the movement as your knee returns to the start position and then repeat.