Knee injuries are among the most common maladies that can set your running back. Given that you strike the ground close to 1,000 times per mile with each leg, it's not surprising that your knees are susceptible to a variety of woes involving bones, tendons, ligaments, muscles and cartilage. Sometimes, knee pain at the start of the run actually subsides once you get going, offering clues as to the genesis of the underlying problem.
Common Injuries
According to the American Academy of Orthopaedic Surgeons, knee injuries account for about one-third of the injuries that runners incur. The most common ones are patellofemoral syndrome, in which the kneecap fails to track properly as it moves up and down; iliotibial band syndrome, which results from a tight fascia lata along the thigh and causes lateral knee pain; and chondromalacia patellae, in which knee cartilage damage results from excessive impact stresses. In each of these, pain that is present when you begin a run can temporarily subside as a result of warming up and changing the surfaces on which you run.
Running Surface
You may be one of many runners who begins a workout on hard concrete or asphalt that eventually gives way to softer grass or dirt or perhaps a rubberized track. If you notice knee pain subsiding as your run progresses, it is likely because of a combination of not doing proper warm-up and stretching exercises and subjecting your knees to the abundant stresses imposed by asphalt roads and concrete sidewalks, neither of which nature had in mind during the evolution of the human body. You should always try to limit your running to soft surfaces, including a treadmill if necessary.
Topography
Running up and down hills, on uneven surfaces such as rough trails or unimproved gravel roads, or both place extra stress on all of your muscles and joints. Downhill running is an established aggravator of knee pain, as the quadriceps often cannot contract forcefully enough to keep your patella from smacking into the bottom of the joint owing to gravity, and iliotibial band syndrome in particular is worse on crowned roads and other banked terrain. If your knee pain abates as you transition to flat, smooth surfaces, you may need to avoid hills entirely until your injury heals.
Pace
It is natural for your running pace to change during the course of a run. More experienced runners know to begin more slowly to allow the muscles and cardiovascular system to warm up, while less experienced runners often begin too fast. Some knee injuries worsen with a faster pace, while some injuries are actually more painful at "shuffling" paces typical of the beginnings of workouts. If your knee pain lessens during a run, be aware of the different paces you run and try to correlate them with an improvement or worsening of knee symptoms as a guide to keeping trouble at bay.
