People have used lubricants to improve movement in machines throughout history. We still oil parts and pieces so they glide over each other instead of grinding and causing damage. Your body has natural lubricants inside it, like bursae, to protect its own moving parts. These little structures themselves aren’t immune to damage, though; irritation can lead to painful bursitis.
Painful Inflammation Problems
Bursitis is irritation and inflammation in a support structure called a bursa. This is a fluid-filled sac that sits between bones and the tendons, muscles, and skin around them. It acts as a protective layer, so friction from your movements don’t cause injury to the soft tissues. However, repetitive motions and stress can damage the bursa itself, painfully inflaming the sac.
In your feet, you can develop the problem under the ball of the foot or, more commonly, behind the heel where the Achilles tendon attaches to the calcaneus, or heel bone. The bursa there is meant to protect the Achilles from rubbing against your heel, but repetitive pressure and hard impacts from your steps can aggravate it. Usually this happens with poor conditioning or insufficient warmups before an activity, so athletes have a particularly high risk. This is also common if you have a bony protrusion on your calcaneus called a Haglund’s deformity.