Inter-Session Reliability of Markerless Motion Capture Across Common Athletic Movement Tasks

Summary

A 2025 study from KU Leuven, Liverpool John Moores University, and collaborators evaluated whether Theia3D can reliably measure lower-extremity joint kinematics and kinetics across two separate testing sessions during common return to training (RTS) tasks.

Editor's Note: The following summary details independent academic research conducted in clinical research settings. Theia3D is an offline software solution engineered exclusively for research and human performance analysis.

Why This Matters

Return to training decisions increasingly rely on movement-quality analysis, not just performance metrics (e.g. hop distance or T-test time). Traditional marker-based motion capture offers high accuracy but requires considerable setup time and specialized resources, which can make frequent RTS assessments challenging in many research or field environments.

Markerless systems promise faster, more scalable biomechanical assessment, but only if they demonstrate strong test-retest reliability, meaning practitioners can trust that measured changes between sessions reflect meaningful changes in the movement.

This study directly addresses the key question practitioners, sports scientists, and performance staff have been asking:

‍Can markerless motion capture reliably capture high-impact, multiplanar RTS tasks – across different days – well enough to track recovery research progress?

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Study Overview

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Participants

18 healthy adults (12 male, 6 female)
Two test sessions ~1 week apart

Tasks Assessed

A comprehensive battery representing real RTS challenges: Countermovement jump (CMJ), Crossover hop (COH), Drop vertical jump (DVJ), Single-leg drop vertical jump (SLDVJ), Single-leg hop, Sidestep cutting (SSC).

Measurement Setup
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Recorded with 8 Qualisys Miqus video cameras + dual force plates
Processed through Theia3D → Visual3D for joint angles & external moments
Evaluated sagittal & frontal planes (transverse excluded due to known unreliability)

Analysis Metrics
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Integrated ICCs for full time-series reliability
Discrete ICCs for key events (initial contact, peak values)
SEM and MDC to determine whether real research change can be detected

Key Findings
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1. Strong Reliability for Most Kinematic Measures
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Across all tasks and joints, joint angles showed moderate-to-excellent test-retest reliability (Sagittal: ICC 0.61–0.86; Frontal: ICC 0.62–0.90). This indicates practitioners can confidently use markerless systems to evaluate joint flexion/extension and ab/adduction between sessions.

2. MDC Values Suggest good Sensitivity for Kinematics
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MDC ranges for joint angles aligned with ACL recovery research improvements (e.g., 5–10° changes). However, kinetic MDCs – especially hip/ankle – were sometimes larger than typical recovery research-driven changes, meaning kinetics should be interpreted cautiously if looking for subtle week-to-week improvements.
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What This Means for Practitioners, Researchers, and Performance Staff
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Multi-session testing (e.g. weekly monitoring) is feasible without concern for major measurement drift. Cutting and single-leg tasks remain highly reliable in kinematics, even if kinetics show variability. These results support the use of markerless motion capture as a practical solution for athlete monitoring workflows, particularly in settings where speed, scalability, and reduced setup complexity matter.

Read the full article here.

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