Closed chain IRQ into ball (Knee terminal extension strengthening, pushing heel into ball, sitting)

Sit with your legs straight out in front of you.
Place a small ball against a wall.
Put the foot of your affected leg flat up against the ball, with your knee slightly bent.
Keep your knee pointing directly upwards.
Push the heel of your foot in to the ball, trying to straighten your knee.
Use the resistance of the ball to push against so you feel the movement.