Single-leg hip flexion in crook lying - short lever

Lie on your back with your knees bent and your feet flat on the floor.
Tighten your abdominal muscles.
Lift one leg, bringing your knee in towards your chest.
Do not let your knee drift in and out whilst moving this leg.
Slowly lower your leg back to the starting position and place your foot back on to the floor.
Keep the movement controlled.