Resisted hip flexion in sitting (Hip flexion strengthening, with band, sitting)

Sit up straight in a chair with a resistance band tied around your lower thighs, just above your knees.
There should be tension in the band with your legs together on the chair.
Sitting up tall, tighten your tummy muscles and then raise one knee up.
The movement should come from your hip.
Control the movement against the pull of the band as you lower your thigh back onto the chair and repeat.