This exercise is great for strengthening your quadriceps, hips and knees.
You can perform it without any equipment.
Lie on your back on an exercise mat.
One leg is forming 45 degree angle in knee, your other leg is extended and resting on exercise mat.
Slowly rise extended leg so it forms 45 degree angle with the floor.
Slowly return to basic position.
After repeating this motion several times, change legs.
You can use ankle weights