Your legs carry the full weight of your body across an estimated 100,000 miles in a lifetime — roughly four times around the Earth. The joints that make this possible are remarkable engineering, but they are subject to decades of cumulative loading, and their maintenance is heavily influenced by how you treat them.
Articular cartilage — the smooth tissue covering the ends of bones in joints — has very limited regenerative capacity. Unlike most tissues in the body, it has no blood supply of its own, relying instead on the diffusion of nutrients through joint fluid. This makes it slow to repair and vulnerable to cumulative damage.
Many people avoid exercise fearing it will "wear out" their joints — but the evidence shows the opposite. Regular moderate exercise builds muscle support around joints, reduces loading per step, and delivers nutrients to cartilage through joint fluid movement. Inactivity is worse for joints than exercise.
Blood flow to the legs and feet declines with age as arteries stiffen and peripheral resistance increases. Smoking particularly impairs peripheral circulation — peripheral arterial disease (PAD) affects roughly 20% of people over 60 and is strongly linked to smoking history. Symptoms include leg pain when walking that eases at rest.