The idea that running on concrete inevitably destroys the knees is a common concern among runners. This fear stems from the noticeable hardness of concrete compared to softer surfaces like trails or tracks. Understanding the actual physics of impact and the primary factors that cause knee pain provides a more complete answer than simply blaming the sidewalk. This article examines the scientific reality of running surfaces and the elements that truly determine knee stress and injury risk.
The Direct Answer: Concrete vs. Impact Force
Concrete is the least compliant of common running surfaces, offering almost no energy absorption. For comparison, asphalt can reduce peak impact forces by approximately 8–12%, and synthetic tracks are engineered for higher energy return. Studies measuring ground reaction forces consistently show that concrete generates the highest peak impact forces, meaning the runner’s body must do more work to absorb the shock of landing.
The human body is designed to manage these forces through a complex system of shock absorption involving the joints, tendons, and muscles. When landing on a hard surface like concrete, the nervous system quickly adjusts the stride mechanics. This adjustment typically involves increasing the stiffness of the lower leg muscles, such as the calves, to better manage the rapid impact.
The surface material itself is not the sole factor determining injury risk; a runner’s form and musculature play a larger role in mitigating the force. While concrete requires the body to compensate more, the primary concern is the repetitive nature of the stress it imposes on passive structures like bones and ligaments. This repetitive stress is what can lead to overuse injuries like patellofemoral pain syndrome (runner’s knee) or stress fractures over time.
Factors That Truly Influence Knee Stress
The greatest contributors to knee issues are related to training errors and biomechanical limitations, rather than the running surface itself. A common cause of running-related pain is the “too much, too soon” principle, referring to a rapid increase in training volume or intensity. Significant increases in weekly mileage are strongly correlated with higher joint load measures, such as tibiofemoral and patellofemoral forces. The joints and surrounding tissues cannot adapt quickly enough to the sudden rise in repetitive stress.
Biomechanical errors also place undue strain on the knee joint, regardless of the running surface. Overstriding, where the foot lands significantly in front of the center of gravity, increases braking forces and the impact on the knee upon landing. This movement pattern forces the knee to act more like a shock absorber, accelerating wear on the joint.
Muscular weakness and imbalances are a primary driver of knee stress. Weakness in the core, glutes, and hips leads to poor control of the leg during the running stride. When hip muscles lack strength, the thigh may rotate inward excessively, causing the knee to collapse medially (dynamic knee valgus). This misalignment heightens the risk for overuse injuries like patellofemoral pain syndrome and Iliotibial Band (IT band) syndrome.
Mitigation Strategies for Running Hard Surfaces
Runners who frequently use concrete can take steps to reduce the risk of knee discomfort and injury. Maintaining a consistent shoe rotation and replacing worn-out footwear is important, as shoes lose their cushioning and supportive properties over time. Choosing a shoe that provides adequate support and cushioning for one’s specific foot type helps manage the impact forces transmitted through the lower body.
Adjusting running form to minimize impact is an effective strategy. Increasing the running cadence, or step rate, to approximately 170 to 180 steps per minute naturally shortens the stride length and reduces overstriding. This adjustment encourages the foot to land closer to the body’s center of gravity, decreasing the peak braking forces and the resulting stress on the knee.
Incorporating regular strength training is the most protective measure a runner can take. Focusing on exercises that target the posterior chain, such as the glutes and hamstrings, helps stabilize the hip and knee joints. Strengthening the gluteal muscles and the core ensures the knee tracks correctly and prevents excessive inward movement of the leg during the stride.
Varying the running surface whenever possible prevents the accumulation of repetitive strain injuries. Alternating concrete runs with softer surfaces like grass, dirt trails, or a synthetic track distributes the impact forces across different muscles and connective tissues. This varied terrain approach allows the body to recover from the higher impact demands of concrete.