The Concurrent Validity and Test-Retest Reliability of a Smartphone-Based Markerless System

Area of Science:

• Sports Science
• Biomechanics
• Human Movement Analysis

Background:

• Accessible and portable biomechanical data aids sports scientists in data-driven decision-making.
• Markerless motion capture systems offer potential for increased accessibility in sports analysis.

Purpose of the Study:

• To assess the concurrent and convergence validity of a smartphone-based markerless system for biomechanical analysis.
• To evaluate the test-retest reliability of this smartphone system for sports performance tracking.

Main Methods:

• Concurrent recording of countermovement jumps using iPhones with Uplift Labs software and a Qualisys marker-based system.
• Statistical analysis included Bland-Altman limits of agreement, mixed-effect linear regressions, and intraclass correlation coefficients (ICC).

Main Results:

• The smartphone system exceeded a priori limits for concurrent validity but demonstrated acceptable convergence validity.
• Test-retest reliability (ICC) for the smartphone system was high (95.5%), comparable to the marker-based system (94.4%).

Conclusions:

• The smartphone-based markerless system shows promise for tracking athlete performance changes within sessions due to its reliability.
• Further validation may be needed for precise concurrent biomechanical measurement across different athletes or conditions.