10.1 Motion capture systems and technologies

Motion capture systems are crucial tools in sports biomechanics. They come in three main types: optical, non-optical, and markerless. Each system has unique characteristics, offering different levels of accuracy, portability, and ease of use for various sports applications.

Choosing the right motion capture system depends on factors like the specific sport, required accuracy, and research goals. Optical systems excel in controlled environments, while inertial and markerless systems offer more flexibility for field use. Understanding each system's strengths and limitations is key to effective biomechanical analysis.

Motion capture systems in sports

Types and characteristics

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  Dual Kinect v2 system can capture lower limb kinematics reasonably well in a clinical setting ... View original

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  Frontiers | Evaluation of 3D Markerless Motion Capture Accuracy Using OpenPose With Multiple ... View original

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• 

  Dual Kinect v2 system can capture lower limb kinematics reasonably well in a clinical setting ... View original

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  Frontiers | Evaluation of 3D Markerless Motion Capture Accuracy Using OpenPose With Multiple ... View original

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• Motion capture systems categorized into three main types optical, non-optical, and markerless systems
• Optical systems track reflective markers on athlete's body using multiple cameras
  • Provide high accuracy for detailed movement analysis in controlled environments
• Non-optical systems include inertial measurement units (IMUs) and electromagnetic systems
  • Offer portability and capture motion in various environments without camera limitations
• Markerless systems utilize computer vision and AI algorithms to track human movement
  • Enable more natural and unrestricted motion analysis without physical markers
• Active marker systems emit their own light signals
• Passive marker systems use reflective markers illuminated by external light sources

Applications and selection factors

• Applications in sports biomechanics include performance analysis, injury prevention, rehabilitation monitoring, and equipment design optimization
• System choice depends on specific sport, required accuracy, environment, and research or training objectives
• Factors to consider include capture volume, movement complexity, and desired outcome measures
• Environmental adaptability crucial for systems intended for field use or varying locations

Optical, Inertial, and Markerless motion capture

Optical systems

• Rely on triangulation principle to determine 3D marker positions
• Use multiple cameras to capture 2D projections of markers
• High accuracy and precision ideal for laboratory-based analysis (gymnastics, figure skating)
• Limited by occlusion issues and need for controlled environment with proper lighting
• Restricted capture volume and complex setup

Inertial systems

• Utilize accelerometers, gyroscopes, and magnetometers
• Measure linear acceleration, angular velocity, and orientation of body segments
• Portable and capable of capturing motion in natural environments (soccer, skiing)
• May have lower absolute position accuracy compared to optical systems
• Can suffer from drift errors over time
• Require periodic recalibration or sensor data fusion to maintain accuracy

Markerless systems

• Employ computer vision techniques like pose estimation algorithms and deep learning models
• Identify and track human body landmarks without physical markers
• Allow quick setup and natural movement without marker placement
• Beneficial for team sports analysis or rapid assessment of multiple athletes
• Face challenges in accurately tracking complex or rapid movements
• May have lower precision compared to marker-based systems, especially for fine motor movements

Motion capture system advantages and disadvantages

Optical systems

• Advantages
  • High accuracy and precision
  • Ideal for complex movement analysis (gymnastics, figure skating)
• Disadvantages
  • Restricted capture volume
  • Complex setup
  • Occlusion issues
  • Require controlled environment and proper lighting

Inertial systems

• Advantages
  • Portable
  • Capture motion in natural environments
  • Suitable for field-based sports (soccer, skiing)
• Disadvantages
  • Lower absolute position accuracy compared to optical systems
  • Drift errors over time
  • Require periodic recalibration

Markerless systems

• Advantages
  • Quick setup
  • Allow natural movement without marker placement
  • Beneficial for team sports analysis and rapid athlete assessment
• Disadvantages
  • Lower precision for detailed biomechanical research
  • Challenges in tracking complex or rapid movements

Active and passive marker systems

• Active marker advantages
  • Operate in varying light conditions
  • Automatically identify markers
  • Useful for outdoor sports and large capture volumes
• Active marker disadvantages
  • Require power sources for each marker
• Passive marker advantages
  • More cost-effective
  • Allow smaller markers
  • Beneficial for analyzing fine motor skills (golf, archery)
• Passive marker disadvantages
  • May suffer from marker swapping or confusion in complex movements

Electromagnetic systems

• Advantages
  • Capture motion without line-of-sight requirements
  • Advantageous for sports with equipment obstruction (motorsports)
• Disadvantages
  • Susceptible to magnetic interference
  • Limited range

Suitability of motion capture systems

Accuracy considerations

• Spatial resolution affects precision of position measurements
• Temporal resolution determines ability to capture rapid movements
• System's capability to capture specific movement characteristics relevant to sport or research question
• All technologies subject to soft tissue artifact introducing errors in joint angle calculations

Cost factors

• Initial equipment investment varies significantly between system types
• Ongoing maintenance costs differ based on system complexity
• Software licenses may require regular renewals
• Potential facility modifications for system installation and operation

Ease of use and expertise requirements

• Setup time ranges from quick (markerless) to complex (optical)
• Calibration procedures vary in complexity and frequency
• Data processing requirements differ between systems
• Level of expertise needed to operate system and interpret results varies

Data integration and scalability

• Data output format affects compatibility with other biomechanical analysis tools
• Integration capabilities influence utility in comprehensive research or training programs
• Scalability includes ability to expand capture volume or add sensors/cameras
• Long-term viability depends on adaptability to evolving research needs

Support and maintenance

• User support includes training resources and technical assistance
• Software updates ensure system remains current with technological advancements
• Availability of replacement parts and repair services affects long-term reliability
• User community and forums provide additional resources and troubleshooting support