Downhill running places more stress on your knees than running uphill or on flat ground, as your muscles and your joints are stressed with additional body weight. Weak leg muscles, mechanical conditions and foot placement can further aggravate your knee joint, leading to pain when you are running downhill. Talk to your doctor to determine the cause of your pain, and avoid running downhill until your pain alleviates.
Patellofemoral Pain Syndrome
Characterized by pain running or walking downhill, patellofemoral pain syndrome, or PFPS, is one of the most common knee injuries among runners, according to podiactric sports medicine practitioner Dr. Stephen M. Pribut. Also called runner's knee, anterior knee pain or chondromalacia of the patella, PFPS involves your quadriceps -- front thigh muscles -- your knee cap and your patellar tendon. If your knee cap does not track correctly during joint motion, the cartilage in your knee joint can wear down at certain points. Typically, this deterioration occurs toward the inside of the knee. If you have proper knee cap movement, cartilage damage can occur from uneven stresses in your joint.
Muscle Weakness
Muscle weaknesses in your upper legs can lead to improper movement of your knee cap. Your thigh muscles, like the quadricep, hold your knee cap in place and help maintain its track. The back of your thighs -- your hamstrings -- are more often developed during running, particularly long distance. Your quadriceps, in comparison, are used less. This imbalance is enough to allow your kneecap to pull and twist to the side. Cross-training with weights or exercises that strengthen your quadriceps, hips and inner and outer thighs can improve your overall strength, prevent injuries and potentially boost your running performance.
Mechanical Conditions
Anatomical positioning plays a large role in potential knee injuries. Having wider hips increases the angle of the thigh bone as it meets the knee joint, thereby increasing the stress on the joint itself. A condition called Genu Valgum -- or knock-knees -- will also place more force on the knee joint, potentially wearing down cartilage. Another cause of knee pain is a misaligned knee cap. If your knee cap is naturally placed higher than the average person, it can track incorrectly.
Foot Placement
The way your feet hit the ground is also crucial to your knees' longevity. If you over-pronate, or are flat-footed, you will also increase the torque on your knee joint. Running consistently, especially downhill, on flat feet can very often lead to pain and PFPS. Your doctor can recommend special shoe inserts that lift the insides of your feet so they strike properly on the ground.
