Ability of sagittal kinematic variables to estimate ground reaction forces and joint kinetics in running.

STUDY
DESIGN: Controlled laboratory study, cross-sectional design.
OBJECTIVE: To determine if sagittal kinematic variables can be used to estimate select running kinetics.
BACKGROUND: Excessive loading during running has been implicated in a variety of injuries, yet this information is typically not assessed during a standard clinical examination. Developing a clinically feasible strategy to estimate ground reaction forces and joint kinetics may improve the ability to identify those at an increased risk of injury.
METHODS: Three-dimensional kinematics and ground reaction forces of 45 participants were recorded during treadmill running at self-selected speed. Kinematic variables used to estimate specific kinetic metrics included vertical excursion of the center of mass, foot inclination angle at initial contact, horizontal distance between the center of mass and heel at initial contact, knee flexion angle at initial contact, and peak knee flexion angle during stance. Linear mixed-effects models were fitted to explore the association between the kinetic and kinematic measures, including step rate and sex, with final models created using backward variable selection.
RESULTS: Models were developed to estimate peak knee extensor moment (R(2) = 0.43), energy absorbed at the knee during loading response (R(2) = 0.58), peak patellofemoral joint reaction force (R(2) = 0.55), peak vertical ground reaction force (R(2) = 0.48), braking impulse (R(2) = 0.50), and average vertical loading rate (R(2) = 0.04).
CONCLUSION: Our findings suggest that insights into important running kinetics can be obtained from a subset of sagittal plane kinematics common to a clinical running analysis. Of note, the limb posture at initial contact influenced subsequent loading patterns in stance.