The effects of marathon running on three-dimensional knee kinematics during walking and running in recreational runners.

BACKGROUND Running-related musculoskeletal injuries are common. Knee injuries are most frequent, and often occur during or shortly after marathons. RESEARCH QUESTION The effects of a marathon on runners' knee kinematics remain unclear. No studies have shown comprehensive three-dimensional (3D) knee kinematic changes following a marathon. This study aimed to observe the effects of running a marathon on 3D knee kinematics and identify the phases of walking and running gait in which significant changes occur. METHODS Based on an electronic survey, 10 healthy, recreational runners (20 knees) with similar running experience were included. Their 3D knee kinematics (during treadmill walking and running) were collected using a portable, optical motion capture system within 24 h before and within 6 h after running a marathon. RESULTS All measurements after the marathon were compared with pre-marathon measurements. (1) For walking post-marathon: varus rotation increased by 1.8° [95% confidence interval (CI) 0.1-3.4, P = 0.036] at peak knee extension during stance; anterior translation increased by 2.2 mm (95% CI 0.3-4.1, P = 0.025) at initial contact; range of motion (ROM) in internal-external rotation increased less than 1°, P = 0.023; ROM in anteroposterior translation increased by 3.8 mm, P = 0.048. (2) For running post-marathon: flexion rotation increased by 1.6° (95% CI 0.2-2.9, P = 0.025) at initial contact; varus rotation increased by 2.0° (95% CI 0.2-3.8, P = 0.031) at peak knee extension during stance. SIGNIFICANCE Significant differences in varus rotation and anterior translation were identified following a marathon, which could potentially contribute to injury. These results provide important information for runners and coaches about knee kinematic alterations following a marathon.