Validity and reliability of a smartphone motion analysis app for lower limb kinematics during treadmill running.

Objective: To investigate the validity and reliability of a smartphone application for selected lower-limb kinematics during treadmill running.
Design: Validity and reliability study.
Setting: Biomechanics laboratory.
Participants: Twenty healthy female runners.
Main Outcome Measure(s): Sagittal-plane hip, knee, and ankle angle and rearfoot eversion were assessed using the Coach's Eye Smartphone application and a 3D motion capture system. Paired t-test and intraclass correlation coefficients (ICC) established criterion validity of Coach's Eye; ICC determined test-retest and intrarater/interrater reliability. Standard error of measurement (SEM) and minimal detectable change (MDC) were also reported.
Results: Significant differences were found between Coach's Eye and 3D measurements for ankle angle at touchdown and knee angle at toe-off (p < 0.05). ICCs for validity of Coach's Eye were excellent for rearfoot eversion at touchdown (ICC = 0.79) and fair-to-good for the other kinematics (range 0.51-0.74), except for hip at touchdown, which was poor (ICC = 0.36). Test-retest (range 0.80-0.92), intrarater (range 0.95-0.99) and interrater (range 0.87-0.94) ICC results were excellent for all selected kinematics.
Conclusion: Coach's Eye can be used as a surrogate for 3D measures of knee and rearfoot in/eversion at touchdown, and hip, ankle, and rearfoot in/eversion at toe-off, but not for hip and ankle at touchdown or knee at toe-off. Reliable running kinematics were obtained using Coach's Eye, making it suitable for repeated measures.
Competing Interests: Declaration of competing interest This study did not target a product promotion of either the Samsung smartphone or camera or the Coach’s Eye app used in the current study. None of these companies were involved in any part of the research.
(Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)