Abstract
Falls are a major cause of unintentional injuries. Understanding the movements of the body during falls is important to the design of fall prevention and management strategies, including exercise programs, mobility aids, fall detectors, protective gear, and safer environments. Video footage of real-life falls is increasingly available, and may be used with digitization software to extract kinematic features of falls. We examined the validity of this approach by conducting laboratory falling experiments, and comparing linear and angular positions and velocities measured from 3D motion capture to estimates from Kinovea 2D digitization software based on standard surveillance video (30 Hz, 640x480 pixels). We also examined how Kinovea accuracy depended on fall direction, camera angle, filtering cut-off frequency, and calibration technique. For a camera oriented perpendicular to the plane of the fall (90 degrees), Kinovea position data filtered at 10 Hz, and video calibration using a 2D grid, mean root mean square errors were 0.050 m or 9% of the signal amplitude and 0.22 m/s (7%) for vertical position and velocity, and 0.035 m (6%) and 0.16 m/s (7%) for horizontal position and velocity. Errors in angular measures averaged over 2-fold higher in sideways than forward or backward falls, due to out-of-plane movement of the knees and elbows. Errors in horizontal velocity were 2.5-fold higher for a 30 than 90 degree camera angle, and 1.6-fold higher for calibration using participants' height (1D) instead of a 2D grid. When compared to 10 Hz, filtering at 3 Hz caused velocity errors to increase 1.4-fold. Our results demonstrate that Kinovea can be applied to 30 Hz video to measure linear positions and velocities to within 9% accuracy. Lower accuracy was observed for angular kinematics of the upper and lower limb in sideways falls, and for horizontal measures from 30 degree cameras or 1D height-based calibration.
Highlights
Falls are the number one cause of unintentional injury and the number two cause of injuryrelated deaths world-wide [1,2]
Our results provide a Accuracy of Kinovea software in estimating body segment movements during falls basis for understanding what can be accurately measured, and for recommended approaches for using Kinovea to analyze the kinematics of falls from 2D planar video
3.2 Effect of fall direction and body part on the accuracy of fall kinematics measured by Kinovea
Summary
Falls are the number one cause of unintentional injury and the number two cause of injuryrelated deaths world-wide [1,2]. Falls cause 37 million hospital visits, 646,000 fatalities [2], and treatment costs over USD 50 billion globally [3]. Falls cause up to 80% of traumatic brain injuries [4] and 95% of hip fractures [5,6] in older adults. Improved understanding of the kinematics of real-life falls should help to inform efforts for injury prevention. Data on the kinematics of falls can guide the design of improved sensor-based automatic fall detection systems [18,19,20,21,22,23]. Data on the impact velocities of the body during falls is essential for the design and evaluation of fall protective gear [24,25,26,27,28] and compliant flooring
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