Context: Lower-extremity landing mechanics have been implicated as a contributing factor in knee pain and injury, yet cost-effective and clinically accessible methods for evaluating movement mechanics are limited. The identification of valid, reliable, and readily accessible technology to assess lower-extremity alignment could be an important tool for clinicians, coaches, and strength and conditioning specialists. Objective: To examine the validity and reliability of using a handheld tablet and movement-analysis application (app) for assessing lower-extremity alignment during a drop vertical-jump task. Design: Concurrent validation. Setting: Laboratory. Participants: 22 healthy college-age subjects (11 women and 11 men, mean age 21 ± 1.4 y, mean height 1.73 ± 0.12 m, mean mass 71 ± 13 kg) with no lower-extremity pathology that prevented safe landing from a drop jump. Intervention: Subjects performed 6 drop vertical jumps that were recorded simultaneously using a 3-dimensional (3D) motion-capture system and a handheld tablet. Main Outcomes Measures: Angles on the tablet were calculated using a motion-analysis app and from the 3D motion-capture system using Visual 3D. Hip and knee angles were measured and compared between both systems. Results: Significant correlations between the tablet and 3D measures for select frontal- and sagittal-plane ranges of motion and angles at maximum knee flexion (MKF) ranged from r = .48 (P = .036) for frontal-plane knee angle at MKF to r = .77 (P < .001) for knee flexion at MKF. Conclusion: Results of this study suggest that a handheld tablet and app may be a reliable method for assessing select lower-extremity joint alignments during drop vertical jumps, but this technology should not be used to measure absolute joint angles. However, sports medicine specialists could use a handheld tablet to reliably record and evaluate lower-extremity movement patterns on the field or in the clinic.
The authors are with the Dept of Physical Therapy, Ithaca College, Ithaca, NY.