Knee Pain While Running: Causes, Prevention, and Management

Why does my knee hurt when I run but not when I walk?

Knee pain during running, but not walking, typically indicates that the increased forces, joint loading, and specific muscle activation patterns inherent to running are exacerbating an underlying biomechanical issue, muscular imbalance, or structural sensitivity that is not sufficiently stressed during the lower-impact activity of walking.

Understanding the Biomechanical Differences Between Running and Walking

The fundamental difference between running and walking lies in the magnitude and nature of the forces exerted on the body, particularly the lower extremities.

• Impact Forces: Running involves a flight phase where both feet are off the ground, leading to higher impact forces upon landing. These ground reaction forces can be 2-3 times your body weight during walking, but escalate to 5-7 times or more during running. This significantly increases the stress on joints, ligaments, tendons, and muscles.
• Joint Loading: The knee joint experiences greater compressive and shear forces during running. The angles at which the knee flexes and extends, and the speed of these movements, are also more extreme during running, placing different demands on the patellofemoral joint (kneecap and thigh bone) and surrounding structures.
• Muscle Activation: Running requires more dynamic and powerful muscle contractions, especially from the quadriceps, hamstrings, glutes, and calf muscles, to propel the body forward and absorb impact. Weakness or imbalances in these muscles, which might be compensated for during walking, become evident and problematic under the higher demands of running.
• Movement Patterns: Running involves greater range of motion at the hip and knee, along with more pronounced rotational forces, especially if there are underlying issues with hip stability or foot mechanics.

Common Causes of Knee Pain During Running

Several conditions are frequently aggravated by the unique biomechanics of running, leading to pain that is absent during walking.

• Patellofemoral Pain Syndrome (PFPS) – Runner's Knee: This is one of the most common causes. It presents as diffuse pain around or behind the kneecap. During running, the patella tracks improperly in its groove on the femur, often due to muscle imbalances (e.g., weak vastus medialis obliquus, tight IT band, weak gluteus medius) or biomechanical issues (e.g., excessive pronation). The repetitive bending and loading of the knee during running intensifies this maltracking, leading to irritation.
• Iliotibial Band Syndrome (ITBS): The IT band is a thick band of fascia running along the outside of the thigh from the hip to just below the knee. ITBS occurs when the IT band becomes tight or inflamed, often due to repetitive friction over the lateral femoral epicondyle (bony prominence on the outside of the knee) during knee flexion and extension, particularly around 30 degrees of knee flexion, a common angle during the stance phase of running.
• Patellar Tendinopathy (Jumper's Knee): This involves inflammation or degeneration of the patellar tendon, which connects the kneecap to the shin bone. The repetitive, high-force eccentric loading of the quadriceps during the landing phase of running can overload this tendon, leading to pain just below the kneecap.
• Meniscal Injuries: While acute meniscal tears are often traumatic, degenerative tears or pre-existing minor damage to the menisci (cartilage pads in the knee) can become symptomatic with the increased compression and shear forces experienced during running.
• Osteoarthritis (OA): If you have early-stage knee osteoarthritis, the cartilage may be able to handle the low-impact forces of walking without pain. However, the significantly higher impact and rotational forces of running can exacerbate the wear and tear, leading to pain, stiffness, and inflammation.
• Stress Fractures: Though less common for isolated running pain, repetitive stress on the bones, particularly the tibia or femur, can lead to tiny cracks. The increased impact loading of running can cause pain that is absent during walking.

Contributing Factors to Running-Related Knee Pain

Beyond the specific diagnoses, several underlying issues can predispose a runner to knee pain.

• Training Errors:
  • "Too much, too soon": Rapid increases in mileage, intensity, or frequency without adequate adaptation time.
  • Insufficient rest: Not allowing the body enough time to recover and repair.
  • Lack of variety: Always running on the same surface or in the same direction.
• Biomechanical Imbalances:
  • Weak Gluteal Muscles: Weak gluteus medius and maximus can lead to excessive hip adduction (knees collapsing inward) and internal rotation during running, increasing stress on the patellofemoral joint and IT band.
  • Tight Hip Flexors and Hamstrings: Can alter pelvic tilt and stride length, affecting knee mechanics.
  • Foot Mechanics: Excessive pronation (flat feet) or supination (high arches) can transmit abnormal rotational forces up the kinetic chain to the knee.
  • Core Weakness: A weak core compromises overall stability, potentially leading to compensatory movements in the lower limbs.
• Improper or Worn-Out Footwear: Running shoes lose their cushioning and support over time, typically after 300-500 miles. Worn-out shoes or shoes that are not appropriate for your foot type and running style can significantly increase impact forces and alter biomechanics.
• Running Form:
  • Overstriding: Landing with your foot too far in front of your body with a relatively straight knee, which increases braking forces and impact.
  • Low Cadence: A slower stride rate can correlate with higher impact forces and longer ground contact time.
  • Excessive Vertical Oscillation: Bouncing too much rather than moving efficiently forward.
• Running Surface: Consistently running on hard, unforgiving surfaces like concrete can increase impact forces compared to softer surfaces like trails or track.

When to Seek Professional Help

While many running-related knee pains can be managed with rest and self-care, it's important to consult a healthcare professional (e.g., sports medicine physician, physical therapist, orthopedist) if you experience:

• Pain that persists despite rest and modification of activity.
• Significant swelling, redness, or warmth around the knee.
• Instability or a feeling of the knee "giving way."
• Inability to bear weight or perform daily activities without pain.
• Pain accompanied by a popping or clicking sound.
• Numbness or tingling in the leg or foot.

Strategies for Prevention and Management

Addressing knee pain during running requires a multi-faceted approach focused on identifying and correcting the underlying causes.

• Gradual Training Progression: Adhere to the "10% rule," increasing your weekly mileage, intensity, or duration by no more than 10% to allow your body to adapt.
• Strength Training:
  • Gluteal Muscles: Focus on exercises like glute bridges, clam shells, side-lying leg raises, and single-leg squats to improve hip stability.
  • Quadriceps: Strengthen the muscles around the knee with exercises like squats, lunges, and step-ups.
  • Hamstrings and Calves: Include hamstring curls, calf raises, and eccentric heel drops.
  • Core Strength: Planks, bird-dog, and Russian twists improve trunk stability.
• Flexibility and Mobility:
  • IT Band Stretches: Foam rolling the IT band, hip flexor stretches, and piriformis stretches.
  • Hamstring and Quadriceps Stretches: Maintain good flexibility around the knee joint.
  • Ankle Mobility: Ensure adequate ankle dorsiflexion.
• Proper Footwear: Replace running shoes every 300-500 miles. Get fitted at a specialized running store to ensure your shoes are appropriate for your foot type and gait. Consider orthotics if recommended by a professional.
• Running Form Analysis: A running coach or physical therapist can analyze your gait and identify inefficiencies or problematic patterns (e.g., overstriding, low cadence) that contribute to knee pain.
• Warm-up and Cool-down: Always perform a dynamic warm-up before running and a static cool-down with stretching afterward.
• Cross-Training: Incorporate low-impact activities like swimming, cycling, or elliptical training to maintain cardiovascular fitness without overloading the knees.
• R.I.C.E. (Rest, Ice, Compression, Elevation): For acute pain or inflammation, this protocol can help manage symptoms.

By understanding the unique demands running places on your body and proactively addressing any underlying weaknesses or imbalances, you can often mitigate and prevent knee pain, allowing you to enjoy your runs without discomfort.