Begin by standing upright on one leg.
Push your hips backward like you’re going to sit down and bend your knee into a single leg squat position.
Slowly return to the starting position.
Keep your knee aligned with the centre of your foot.

Keep back straight and abs tight 

Dumbbell on the side of the working leg
Leaning on a wall to take an inclined position to do the ankle extensions

Keep back straight and abs tight  

Leaning on the chair
Keep leg and hip straight 

Lay down on your back with knees bent and a ball or pillow between them.
Squeeze the glutes and contract the abdominals to lift the hips off the ground. As you lift, squeeze the ball between the legs.
Hold for a few seconds on top then release as you lower.

Lay down with knees bent about 90° with a weight on the hips for increased resistance.
Lift one leg up and push the hips upward by squeezing the glutes and lower slowly.
Do not arch the lower back. 

Attach an elastic to secure object and to ankle of involved leg.
Lie on your stomach with your knee straight.
Bend your knee through available range without lifting hips.
Return to starting position and repeat.

Anchor the feet under something heavy or have a partner hold them.
Put a towel under the knees or do the exercise on a mat.
Keep the thighs and the trunk in a straight line as much as possible and hinge only at the knees to lower as much as you can then come back up.

Start on one elbow/forearm with the top leg on a chair, knee straight, and the bottom leg on the ground as shown in the picture.
Hold the position with the top leg (do not let the hips drop) and lift the bottom leg up to meet the top leg.
Hold 1 second then go back down without touching the ground and repeat.
Do not rotate pelvis or over arch lower back (ie, maintain alignment
trunk/pelvis/knees at all times) .