Many runners complain of a chronic overuse injury commonly known as runner's knee, but fewer runners understand the causes of their injury. Runner's knee, an injury at the connection of the kneecap and femur, often results from improper use of the muscles in the legs, not the joints, and can force a runner to change the way he runs.
How Your Knee Works
When the bones and muscles of your legs work properly, the patella, commonly known as the kneecap, slides up and down efficiently in a small groove in the femur as the knee bends and straightens. The muscles of your thigh, the hamstrings and quadriceps, hold the patella tightly in place, but weak muscles can allow the patella to slide off track. The patella can also jump its tracks when it does not receive proper support from the feet, whether from flat arches or a stride in which a runner overpronates -- rolling too far inward -- or supinates -- rolling too far outward.
Road Hazards
Runners most commonly induce runner's knee through simple overtraining, increasing their mileage or running intensity too quickly. The effects of overtraining are worsened when runners train on hard surfaces such as roads or sidewalks, which produce a greater impact with each stride than grass, dirt or cinder trails, or synthetic tracks. Cambered roads, which slope toward the side of the road, or banked tracks pose even greater risks for runners, as they force one leg to take a shorter stride than the other, increasing the shorter leg's amount of pronation.
Hill Training
Some runners train on hills to improve strength and increase the intensity of their workouts, but repeatedly running up and down hills can place added strain on a runner's knees. When a runner travels flat surfaces, each running stride can deliver an impact three times the runner's body weight. However, the impact can jump to as high as five to eight times a runner's body weight while running downhill, and the impact is made even worse when a runner's stride is already out of alignment. Running down hills increases the knee's level of compression, adding to the pressure already placed on the joint.
Avoiding Runner's Knee
You can prevent runner's knee even when running regularly on roads or sidewalks by following some simple measures. When running on cambered roads, evenly split the amount of time spent running each direction, so neither leg is forced to pronate more than the other. When running hills, take pressure of your knees by zig-zagging or walking down hills, and avoid excessive hill running when you begin to feel nagging knee pain. Just as importantly, stretch your hamstrings and quadriceps before and after each run to prevent stiffness in the muscles, which can lead to a muscular imbalance.
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