After standing on your feet for a while, do you get a tired, aching feeling at the back of your legs, especially in the calf muscles and behind the knees? To relieve the pain, you might have to take a rest and sit down.
A whole host of problems can cause pain in your lower legs – from muscle fatigue and dehydration to inflamed or torn tendons and muscles to nerve and circulatory problems. But tired, aching legs are commonly caused by strain and traction on the calf muscles at the back of the legs. This can occur when the feet roll over (pronate) and the legs rotate internally. In turn, this places stress on the leg muscles.
For muscle and tendon problems, a simple step like trying orthotics can control excess pronation. This decreases internal rotation of the leg and traction on the calf muscles. It may remove the root cause of the problem.
Source: WebMD. "Lower Leg Pain: Causes and Treatments."