This is a great exercise to improve the flexibility in the quadriceps and glute muscles as well as to improve your overall coordination and sense of balance. After doing Lunges for awhile, you will notice that it is easier to climb stairs, easier to squat down to grab something off of the floor, and that there will be less soreness in your buttocks and legs from prolonged sitting.
You can do Lunges with or without weights depending on your physical condition.
Stand up with your feet together, one hand resting on the back of a chair for balance.
Step back with one leg so that your legs are about 60 degrees apart.
Keep your back straight.
Allow your knees to bend until you touch the floor with the knee of your back leg.
Straighten your legs again.
Repeat 10-15 times for each leg.
If you have knee problems, you may have to modify the Lunge somewhat to make it easier on your knees. One way of doing this is to place a thick book (or some file folders or a briefcase) on the floor in front of your back leg so that your back knee only drops to within six inches from the floor. If this is still too stressful for your knees, just go down as far as you can. The further down you can go, the better the exercise works, as long as you don't strain your knees.