L5 - Biomechanical Measurement Technology

• Purpose of Biomechanical Measurement:

  • To answer a question about a performer's movement

  1. Can you modify an aspect of the technique to improve performance?
  2. Can you gain further understanding of the movement performed (generally or under certain conditions)?
  3. eg rehab/physio (clinical)
  4. Can the movement be modified to reduce the risk of injury (or disease pain)?
• Purpose of Biomechanical Measurement:

  1. Can you modify an aspect of the technique to improve performance?

  • Women’s 100 m sprint final
  • Step length, right to left stride; Relative takes height into account, taller = longer
  • Step rate: amount of steps per second
  • Want optimal bw/ the 2 (step length & rate)
  • Develop fast hip flexion (increase speed)
  • Step width: foot step from centre of lane
• Purpose of Biomechanical Measurement:

  • 2. Can the movement be modified to reduce the risk of injury (or decrease pain)?
  • Fast bowlers (cricket) prone to lower back pain
  • Key factors, lateral bend combined with speed rotating round long axis (crunch factor)
  • How crunch factor change with fatigue
  • Found kinematics changed when tired, turned slower but ball speed stay the same
  • Developed IMU on hand identified bowl & classified intensity (warm-up or comp)
• Video Cameras:

  • Standard video cameras
  • High speed cameras
  • Smartphone/tablet cameras
• Video Cameras:

  • Standard video cameras
  • With manual focus & exposure settings, sufficient for most technique analysis
• Video Cameras:

  • High speed cameras
  • Necessary for specialised analysis
  • High speed impact
  • For high frame rate to capture specific events/phases
• Video Cameras:

  • Smartphone/tablet cameras
  • Fine for informal technique analysis
  • Caution with wide angle lens
  • Causes image distortion
  • Caution with claims of app providers
• 3D Motion Capture (video based):

  • Requires:
  • At least 2 cameras
  • Calibration object
  • Direct linear transform (DLT) to calibrate 3D volume
  • Should have:
  • Markers to improve accuracy
  • Lots of patience
• Calibration:

  • 2D calibration object
  • eg calibration tree
  • Combine view can figure out where things are in space
  • Some for swimming; in & out of water, water got to be still for calibration
• 3D Motion Captures (video based online systems):

  • Vicon, Qualysis most common systems (usually 6-12 cameras)
  • Workflow:
  • Decide on marker set
  • Only on segments interested in
  • Create triangle to represent movement in/out of planes
  • Calibrate space
  • 1) Markers/tool
  • 2) Wand
  • Track markers
  • Collecting trials; marker identification
  • Construct biomedical model
  • Done on software
  • Data analysis & visualisation
  • Create some variables, look at centre of mass
  • Look at things that answer your research question
• Force Plates:

  • Strain gauges detect changes in electrical resistance
  • Sensors under corners
  • Deforms cylinder/strains them changes ER
  • If only interested in vertical = weight scale (standing still)
  • Volts (V) converted to newtons (N)
  • Output 3D forces & torques, 2D centre of pressure
• Force Plates - Applications:

  • Landing & taking off forces
  • Force-time trace (how force changes over time)
  • Impulse
  • Peak & mean forces, loading rates
  • Measure curve
  • Joint loads
  • Inverse dynamics using force & kinematic
  • How much torque (turning force/angle)
• Inertial Measurement Units (IMUs):

  • Usually contain 3 sensors

  1. Accelerometer
  2. Gyroscope
  3. Magnetometer
• Inertial Measurement Units (IMUs):

  • Accelerometer
  • Detect static (eg gravity) & dynamic (eg movement) forces
  • Detect linear movement
  • Can measure linear kinematics
• Inertial Measurement Units (IMUs):

  • Gyroscope
  • Detect rate of angular motion
  • Rotation movement
  • Can measure angular kinematics
• Inertial Measurement Units (IMUs):

  • Magnetometer
  • Detects heading according to magnetic south (or north)
  • Heading movement - eg moving forward
  • Can be used to orient accelerometer & gyroscope readings