The squat is a very beneficial exercise, but it does not develop the legs and hips to as great an extent as is possible. To get a greater ROM in the hip joint due to the greater stretch and contraction of the hip joint extensors, while at the same time creating a greater stretch of the hip flexors, you should do the lunge. This exercise is quite effective and safe for the knee joint when done properly. Its greatest value, however, lies in stretching and strengthening the hip joint muscles.
In order to get these benefits is important that you do what can be called a classic lunge in which a long stride (4-6 feet) is taken. You do not get these benefits if you do what many people call a lunge but which in reality, is closer to what can be called a split squat.
In a split squat you take a short stride so that your feet are no more than 3-5 feet apart. The lowering and raising of the body appears more as a squat exercise rather than a true lunging action. Because of this you must be sure that you do a lunge and not a split squat to get the many benefits, especially for athletes.