Exercises for the quadriceps are those that focus on the muscle group that lie on top of the knee joint in front of the thigh.
These exercises especially strengthen the knee joint and the quadriceps. The following are some exercises that can help:
Sit by the edge of a chair with your feet flat on the ground and the angle of the knees should be at 90 degrees. Now, either one by one or together, lift the leg up slowly till the knee is straight and the leg is out in front of you. Concentrate on your muscles doing the job for you. Do this motion without any jerks, repeating about 6-8 times, 2-3 sets.
Your wife can do this every alternate day. Initially, you will experience some soreness but as you get better at this, you can add some weight to your ankles to make it slightly harder. Make sure that the weight is not too heavy.