Relationship between knee walking kinematics and muscle flexibility in runners.

CONTEXT Decreased flexibility in muscles and joints of lower extremities is commonly observed in runners. Understanding the effect of decreased flexibility on knee walking kinematics in runners is important because, over time, altered gait patterns can make runners vulnerable to overuse injuries or degenerative pathologies. OBJECTIVES To compare hamstring and iliotibial-band (ITB) flexibility and knee kinematics in runners and nonrunners. DESIGN A descriptive, comparative laboratory study. SETTING Hamstring and ITB flexibility were measured with the active knee-extension test and the modified Ober test, respectively, in both groups of participants. Three-dimensional (3D) walking kinematic data were then recorded at the knee using a motiontracking system. PARTICIPANTS 18 runners and 16 nonrunners. MAIN OUTCOME MEASURES Knee-extension angle (hamstring flexibility) and hip-adduction angle (ITB flexibility). Knee kinematic parameters of interest included knee angle at initial contact, peak knee angles, and knee-angle range in all planes of movement. RESULTS The runners had a significantly less flexible ITB than the nonrunners (hip adduction [-] and adduction [+] angles, 3.1° ± 5.6° vs -.4° ± 4.5°; P < .001). The runners demonstrated a greater mean tibial external-rotation angle at initial contact (7.3° ± 5.8° vs 2.0° ± 4.0°; P = .01) and a smaller mean peak tibial internal-rotation angle (-1.6° ± 3.0° vs -4.2° ± 3.2°; P = .04) than the nonrunners. CONCLUSION This study provides new insight into the relationship between muscle flexibility and 3D knee kinematics in runners. This supports the premise that there is an association between muscle flexibility and transverse-plane knee kinematics in this population.