Your body has several mechanisms that serve to act as a shock abosrber when walking, running, jumping and otherwise being active. One of the structures that serves this function is the plantar fat pad--a thick layer of fat on the bottom of your feet that acts as a pillow to the bones of your feet as you walk.
This fat layer is held in place by fibrous tissue often referred to a septae.
Unfortunately, this is one of the few places you need fat on your body, but unfortunately, this one of the few places you tend to lose fat over time as you age.
The problem with a thinning (atrophied) fat pad is that there is less and less cushioning with time, and the patient begins to walk more and more on the bones of the foot, a condition which can be very uncomfortable.
The simplest answer to this problem is using cushioned over-the-counter or even custom-made inserts to help replace the fat as a shock absorber and wearing more cushioned shoes. Your podiatrist can help guide you to the proper type of appliance right for each particular case and foot type.
Injections do exist that act as the atrophied plantar fat pad used to, though their effects tend not to be long-lasting.